Cannabis Breeding and Genetics
by Robert Connell Clarke
Although it is possible to breed Cannabis with limited success without any knowledge of the laws of inheritance, the full potential of diligent breeding, and the line of action most likely to lead to success, is realized by breeders who have mastered a working knowledge of genetics.
As we know already, all information transmitted from generation to generation must be contained in the pollen of the staminate parent and the ovule of the pistillate parent. Fertilization unites these two sets of genetic information, a seed forms, and a new generation is begun. Both pollen and ovules are known as gametes, and the transmitted units determining the expression of a character are known as genes. Individual plants have two identical sets of genes (2n) in every cell except the gametes, which through reduction division have only one set of genes (in). Upon fertilization one set from each parent combines to form a seed (2n).
In Cannabis, the haploid (in) number of chromosomes is 10 and the diploid (2n) number of chromosomes is 20. Each chromosome contains hundreds of genes, influencing every phase of the growth and development of the plant.
If cross-pollination of two plants with a shared genetic trait (or self-pollination of a hermaphrodite) results in offspring that all exhibit the same trait, and if all subsequent (inbred) generations also exhibit it, then we say that the strain (i.e., the line of offspring derived from common ancestors) is true-breeding, or breeds true, for that trait. A strain may breed true for one or more traits while varying in other characteristics. For example, the traits of sweet aroma and early maturation may breed true, while offspring vary in size and shape. For a strain to breed true for some trait, both of the gametes forming the offspring must have an identical complement of the genes that influence the expression of that trait. For example, in a strain that breeds true for webbed leaves, any gamete from any parent in that population will contain the gene for webbed leaves, which we will signify with the letter w. Since each gamete carries one-half (in) of the genetic complement of the offspring, it follows that upon fertilization both “leaf shape” genes of the (2n) offspring will be w. That is, the offspring, like both parents, are ww. In turn, the offspring also breed true for webbed leaves because they have only w genes to pass on in their gametes.
On the other hand, when a cross produces offspring that do not breed true (i.e., the offspring do not all resemble their parents) we say the parents have genes that segregate or are hybrid. Just as a strain can breed true for one or more traits, it can also segregate for one or more traits; this is often seen. For example, consider a cross where some of the offspring have webbed leaves and some have normal compound-pinnate leaves. (To continue our system of notation we will refer to the gametes of plants with compound-pinnate leaves as W for that trait. Since these two genes both influence leaf shape, we assume that they are related genes, hence the lower-case w and uppercase W notation instead of w for webbed and possibly P for pinnate.) Since the gametes of a true-breeding strain must each have the same genes for the given trait, it seems logical that gametes which produce two types of offspring must have genetically different parents.
Observation of many populations in which offspring differed in appearance from their parents led Mendel to his theory of genetics. If like only sometimes produces like, then what are the rules which govern the outcome of these crosses? Can we use these rules to predict the outcome of future crosses?
Assume that we separate two true-breeding populations of Cannabis, one with webbed and one with compound-pinnate leaf shapes. We know that all the gametes produced by the webbed-leaf parents will contain genes for leaf-shape w and all gametes produced by the compound-pinnate individuals will have W genes for leaf shape. (The offspring may differ in other characteristics, of course.)
If we make a cross with one parent from each of the true-breeding strains, we will find that 100% of the offspring are of the compound-pinnate leaf phenotype. (The expression of a trait in a plant or strain is known as the phenotype.) What happened to the genes for webbed leaves contained in the webbed leaf parent? Since we know that there were just as many w genes as W genes combined in the offspring, the W gene must mask the expression of the w gene. We term the W gene the dominant gene and say that the trait of compound-pinnate leaves is dominant over the recessive trait of webbed leaves. This seems logical since the normal phenotype in Cannabis has compound pinnate leaves. It must be remembered, however, that many useful traits that breed true are recessive. The true-breeding dominant or recessive condition, WW or ww, is termed the homozygous condition; the segregating hybrid condition wW or Ww is called heterozygous. When we cross two of the F1 (first filial generation) offspring resulting from the initial cross of the ~1 (parental generation) we observe two types of offspring. The F2 generation shows a ratio of approximately 3:1, three compound pinnate type-to-one webbed type. It should be remembered that phenotype ratios are theoretical. The real results may vary from the expected ratios, especially in small samples.
In this case, compound-pinnate leaf is dominant over webbed leaf, so whenever the genes w and W are combined, the dominant trait W will be expressed in the phenotype. In the F2 generation only 25% of the offspring are homozygous for W so only 25% are fixed for W. The w trait is only expressed in the F2 generation and only when two w genes are combined to form a double-recessive, fixing the recessive trait in 25% of the offspring. If compound-pinnate showed incomplete dominance over webbed, the genotypes in this example would remain the same, but the phenotypes in the F1 generation would all be intermediate types resembling both parents and the F2 phenotype ratio would be 1 compound-pinnate :2 intermediate :1 webbed.
The explanation for the predictable ratios of offspring is simple and brings us to Mendel’s first law, the first of the basic rules of heredity:
I. Each of the genes in a related pair segregate from each other during gamete formation.
A common technique used to deduce the genotype of the parents is the back-cross. This is done by crossing one of the F1 progeny back to one of the true-breeding P1 parents. If the resulting ratio of phenotypes is 1:1 (one heterozygous to one homozygous) it proves that the parents were indeed homozygous dominant WW and homozygous-recessive ww.
The 1:1 ratio observed when back-crossing F1 to P1 and the 1:2:1 ratio observed in F1 to F1 crosses are the two basic Mendelian ratios for the inheritance of one character controlled by one pair of genes. The astute breeder uses these ratios to determine the genotype of the parental plants and the relevance of genotype to further breeding.
This simple example may be extended to include the inheritance of two or more unrelated pairs of genes at a time. For instance we might consider the simultaneous inheritance of the gene pairs T (tall)/t (short) and M (early maturation)/m (late maturation). This is termed a polyhybrid instead of monohybrid cross. Mendel’s second law allows us to predict the outcome of polyhybrid crosses also:
II. Unrelated pairs of genes are inherited independently of each other.
If complete dominance is assumed for both pairs of genes, then the 16 possible F2 genotype combinations will form 4 F2 phenotypes in a 9:3:3:1 ratio, the most frequent of which is the double-dominant tall/early condition. Incomplete dominance for both gene pairs would result in 9 F2 phenotypes in a 1:2:1:2:4:2:1:2:1 ratio, directly reflecting the genotype ratio. A mixed dominance condition would result in 6 F2 phenotypes in a 6:3:3:2:1:1 ratio. Thus, we see that a cross involving two independently assorting pairs of genes results in a 9:3:3:1 Mendelian phenotype ratio only if dominance is complete. This ratio may differ, depending on the dominance conditions present in the original gene pairs. Also, two new phenotypes, tall/late and short/early, have been created in the F2 generation; these phenotypes differ from both parents and grandparents. This phenomenon is termed recombination and explains the frequent observation that like begets like, but not exactly like.
A polyhybrid back-cross with two unrelated gene pairs exhibits a 1:1 ratio of phenotypes as in the monohybrid back-cross. It should be noted that despite dominance influence, an F1 back-cross with the P1 homozygous recessive yields the homozygous-recessive phenotype short/late 25% of the time, and by the same logic, a backcross with the homozygous-dominant parent will yield the homozygous dominant phenotype tall/early 25% of the time. Again, the back-cross proves invaluable in determining the F1 and P1 genotypes. Since all four phenotypes of the back-cross progeny contain at least one each of both recessive genes or one each of both dominant genes, the back-cross phenotype is a direct representation of the four possible gametes produced by the F1 hybrid.
So far we have discussed inheritance of traits controlled by discrete pairs of unrelated genes. Gene interaction is the control of a trait by two or more gene pairs. In this case genotype ratios will remain the same but phenotype ratios may be altered. Consider a hypothetical example where 2 dominant gene pairs Pp and Cc control late-season anthocyanin pigmentation (purple color) in Cannabis. If P is present alone, only the leaves of the plant (under the proper environmental stimulus) will exhibit accumulated anthocyanin pigment and turn a purple color. If C is present alone, the plant will remain green throughout its life cycle despite environmental conditions. If both are present, however, the calyxes of the plant will also exhibit accumulated anthocyanin and turn purple as the leaves do. Let us assume for now that this may be a desirable trait in Cannabis flowers. What breeding techniques can be used to produce this trait?
First, two homozygous true-breeding ~1 types are crossed and the phenotype ratio of the F1 offspring is observed.
The phenotypes of the F2 progeny show a slightly altered phenotype ratio of 9:3:4 instead of the expected 9:3:3:1 for independently assorting traits. If P and C must both be present for any anthocyanin pigmentation in leaves or calyxes, then an even more distorted phenotype ratio of 9:7 will appear.
Two gene pairs may interact in varying ways to produce varying phenotype ratios. Suddenly, the simple laws of inheritance have become more complex, but the data may still be interpreted.
Summary of Essential Points of Breeding
1 – The genotypes of plants are controlled by genes which are passed on unchanged from generation to generation.
2 – Genes occur in pairs, one from the gamete of the staminate parent and one from the gamete of the pistillate parent.
3 – When the members of a gene pair differ in their effect upon phenotype, the plant is termed hybrid or heterozygous.
4 – When the members of a pair of genes are equal in their effect upon phenotype, then they are termed true breeding or homozygous.
5 – Pairs of genes controlling different phenotypic traits are (usually) inherited independently.
6 – Dominance relations and gene interaction can alter the phenotypic ratios of the F1, F2, and subsequent generations.
Polyploidy is the condition of multiple sets of chromosomes within one cell. Cannabis has 20 chromosomes in the vegetative diploid (2n) condition. Triploid (3n) and tetraploid (4n) individuals have three or four sets of chromosomes and are termed polyploids. It is believed that the haploid condition of 10 chromosomes was likely derived by reduction from a higher (polyploid) ancestral number (Lewis, W. H. 1980). Polyploidy has not been shown to occur naturally in Cannabis; however, it may be induced artificially with colchicine treatments. Colchicine is a poisonous compound extracted from the roots of certain Colchicum species; it inhibits chromosome segregation to daughter cells and cell wall formation, resulting in larger than average daughter cells with multiple chromosome sets. The studies of H. E. Warmke et al. (1942-1944) seem to indicate that colchicine raised THC levels in Cannabis. It is unfortunate that Warmke was unaware of the actual psychoactive ingredients of Cannabis and was therefore unable to extract THC. His crude acetone extract and archaic techniques of bioassay using killifish and small freshwater crustaceans are far from conclusive. He was, however, able to produce both triploid and tetraploid strains of Cannabis with up to twice the potency of dipbid strains (in their ability to kill small aquatic organisms). The aim of his research was to “produce a strain of hemp with materially reduced marijuana content” and his results indicated that polyploidy raised the potency of Cannabis without any apparent increase in fiber quality or yield.
Warmke’s work with polyploids shed light on the nature of sexual determination in Cannabis. He also illustrated that potency is genetically determined by creating a lower potency strain of hemp through selective breeding with low potency parents.
More recent research by A. I. Zhatov (1979) with fiber Cannabis showed that some economically valuable traits such as fiber quantity may be improved through polyploidy. Polyploids require more water and are usually more sensitive to changes in environment. Vegetative growth cycles are extended by up to 30-40% in polyploids. An extended vegetative period could delay the flowering of polyploid bud strains and interfere with the formation of floral clusters. It would be difficult to determine if cannabinoid levels had been raised by polyploidy if polyploidplants were not able to mature fully in the favorable part of the season when cannabinoid production is promoted by plentiful light and warm temperatures. Greenhouses and artificial lighting can be used to extend the season and test polyploid strains.
The height of tetraploid (4n) Cannabis in these experiments often exceeded the height of the original diploid plants by 25-30%. Tetraploids were intensely colored, with dark green leaves and stems and a well developed gross phenotype. Increased height and vigorous growth, as a rule, vanish in subsequent generations. Tetraploid plants often revert back to the diploid condition, making it difficult to support tetraploid populations. Frequent tests are performed to determine if ploidy is changing. Triploid (3n) strains were formed with great difficulty by crossing artificially created tetraploids (4n) with dipbids (2n). Triploids proved to be inferior to both diploids and tetraploids in many cases.
De Pasquale et al. (1979) conducted experiments with Cannabis which was treated with 0.25% and 0.50% solutions of colchicine at the primary meristem seven days after generation. Treated plants were slightly taller and possessed slightly larger leaves than the controls, Anomalies in leaf growth occurred in 20% and 39%, respectively, of the surviving treated plants. In the first group (0.25%) cannabinoid levels were highest in the plants without anomalies, and in the second group (0.50%) cannabinoid levels were highest in plants with anomalies, Overall, treated plants showed a 166-250% increase in THC with respect to controls and a decrease of CBD (30-33%) and CBN (39-65%). CBD (cannabidiol) and CBN (cannabinol) are cannabinoids involved in the biosynthesis and degradation of THC. THC levels in the control plants were very low (less than 1%). Possibly colchicine or the resulting polyploidy interferes with cannabinoid biogenesis to favor THC. In treated plants with deformed leaf lamina, 90% of the cells are tetraploid (4n 40) and 10% diploid (2n 20). In treated plants without deformed lamina a few cells are tetraploid and the remainder are triploid or diploid.
The transformation of diploid plants to the tetraploid level inevitably results in the formation of a few plants with an unbalanced set of chromosomes (2n + 1, 2n – 1, etc.). These plants are called aneuploids. Aneuploids are inferior to polyploids in every economic respect. Aneuploid Cannabis is characterized by extremely small seeds. The weight of 1,000 seeds ranges from 7 to 9 grams (1/4 to 1/3 ounce). Under natural conditions diploid plants do not have such small seeds and average 14-19 grams (1/2-2/3 ounce) per 1,000 (Zhatov 1979).
Once again, little emphasis has been placed on the relationship between flower or resin production and polyploidy. Further research to determine the effect of polyploidy on these and other economically valuable traits of Cannabis is needed.
Colchicine is sold by laboratory supply houses, and breeders have used it to induce polyploldy in Cannabis. However, colchicine is poisonous, so special care is exercised by the breeder in any use of it. Many clandestine cultivators have started polyploid strains with colchicine. Except for changes in leaf shape and phyllotaxy, no out standing characteristics have developed in these strains and potency seems unaffected. However, none of the strains have been examined to determine if they are actually polyploid or if they were merely treated with colchicine to no effect. Seed treatment is the most effective and safest way to apply colchicine. * In this way, the entire plant growing from a colchicine-treated seed could be polyploid and if any colchicine exists at the end of the growing season the amount would be infinitesimal. Colchicine is nearly always lethal to Cannabis seeds, and in the treatment there is a very fine line between polyploidy and death. In other words, if 100 viable seeds are treated with colchicine and 40 of them germinate it is unlikely that the treatment induced polyploidy in any of the survivors. On the other hand, if 1,000 viable treated seeds give rise to 3 seedlings, the chances are better that they are polyploid since the treatment killed all of the seeds but those three. It is still necessary to determine if the offspring are actually polyploid by microscopic examination.
The work of Menzel (1964) presents us with a crude map of the chromosomes of Cannabis, Chromosomes 2-6 and 9 are distinguished by the length of each arm. Chromosome 1 is distinguished by a large knob on one end and a dark chromomere 1 micron from the knob. Chromosome 7 is extremely short and dense, and chromosome 8 is assumed to be the sex chromosome. In the future, chromosome *The word “safest” is used here as a relative term. Coichicine has received recent media attention as a dangerous poison and while these accounts are probably a bit too lurid, the real dangers of expoiure to coichicine have not been fully researched. The possibility of bodily harm exists and this is multiplied when breeders inexperienced in handling toxins use colchicine. Seed treatment might be safer than spraying a grown plant but the safest method of all is to not use colchicine. Mapping will enable us to picture the location of the genes influencing the phenotype of Cannabis. This will enable geneticists to determine and manipulate the important characteristics contained in the gene pool. For each trait the number of genes in control will be known, which chromosomes carry them, and where they are located along those chromosomes.
All of the Cannabis grown in North America today originated in foreign lands. The diligence of our ancestors in their collection and sowing of seeds from superior plants, together with the forces of natural selection, have worked to create native strains with localized characteristics of resistance to pests, diseases, and weather conditions. In other words, they are adapted to particular niches in the ecosystem. This genetic diversity is nature’s way of protecting a species. There is hardly a plant more flexible than Cannabis. As climate, diseases, and pests change, the strain evolves and selects new defenses, programmed into the genetic orders contained in each generation of seeds. Through the importation in recent times of fiber and bud Cannabis, a vast pool of genetic material has appeared in North America. Original fiber strains have escaped and become acclimatized (adapted to the environment), while domestic bud strains (from imported seeds) have, unfortunately, hybridized and acclimatized randomly, until many of the fine gene combinations of imported Cannabis have been lost.
Changes in agricultural techniques brought on by technological pressure, greed, and full-scale eradication programs have altered the selective pressures influencing Cannabis genetics. Large shipments of inferior Cannabis containing poorly selected seeds are appearing in North America and elsewhere, the result of attempts by growers and smugglers to supply an ever increasing market for marijuana. Older varieties of Cannabis, associated with longstanding cultural patterns, may contain genes not found in the newer commercial varieties. As these older varieties and their corresponding cultures become extinct, this genetic information could be lost forever. The increasing popularity of Cannabis and the requirements of agricultural technology will call for uniform hybrid races that are likely to displace primitive populations worldwide.
Limitation of genetic diversity is certain to result from concerted inbreeding for uniformity. Should inbred Cannabis be attacked by some previously unknown pest or disease, this genetic uniformity could prove disastrous due to potentially resistant diverse genotypes having been dropped from the population. If this genetic complement of resistance cannot be reclaimed from primitive parental material, resistance cannot be introduced into the ravaged population. There may also be currently unrecognized favorable traits which could be irretrievably dropped from the Cannabis gene pool. Human intervention can create new phenotypes by selecting and recombining existing genetic variety, but only nature can create variety in the gene pool itself, through the slow process of random mutation.
This does not mean that importation of seed and selective hybridization are always detrimental. Indeed these principles are often the key to crop improvement, but only when applied knowledgeably and cautiously. The rapid search for improvements must not jeopardize the pool of original genetic information on which adaptation relies. At this time, the future of Cannabis lies in govern ment and clandestine collections. These collections are often inadequate, poorly selected and badly maintained. Indeed, the United Nations Cannabis collection used as the primary seed stock for worldwide governmental research is depleted and spoiled.
Several steps must be taken to preserve our vanishing genetic resources, and action must be immediate:
Seeds and pollen should be collected directly from reliable and knowledgeable sources. Government seizures and smuggled shipments are seldom reliable seed sources. The characteristics of both parents must be known; consequently, mixed bales of randomly pollinated marijuana are not suitable seed sources, even if the exact origin of the sample is certain. Direct contact should be made with the farmer-breeder responsible for carrying on the breeding traditions that have produced the sample. Accurate records of every possible parameter of growth must be kept with carefully stored triplicate sets of seeds.
Since Cannabis seeds do not remain viable forever, even under the best storage conditions, seed samples should he replenished every third year. Collections should be planted in conditions as similar as possible to their original niche and allowed to reproduce freely to minimize natural and artificial selection of genes and ensure the preservation of the entire gene pool. Half of the original seed collection should be retained until the viability of further generations is confirmed, and to provide parental material for comparison and back-crossing. Phenotypic data about these subsequent generations should be carefully recorded to aid in understanding the genotypes contained in the collection. Favorable traits of each strain should be characterized and catalogued.
It is possible that in the future, Cannabis cultivation for resale, or even personal use, may be legal but only for approved, patented strains. Special caution would be needed to preserve variety in the gene pool should the patenting of Cannabis strains become a reality.
Favorable traits must be carefully integrated into existing strains.
The task outlined above is not an easy one, given the current legal restrictions on the collection of Cannabis seed. In spite of this, the conscientious cultivator is making a contribution toward preserving and improving the genetics of this interesting plant.
Even if a grower has no desire to attempt crop improvement, successful strains have to be protected so they do not degenerate and can be reproduced if lost. Left to the selective pressures of an introduced environment, most bud strains will degenerate and lose potency as they acclimatize to the new conditions. Let me cite an example of atypical grower with good intentions.
A grower in northern latitudes selected an ideal spot to grow a crop and prepared the soil well. Seeds were selected from the best floral clusters of several strains available over the past few years, both imported and domestic. Nearly all of the staminate plants were removed as they matured and a nearly seedless crop of beautiful plants resulted. After careful consideration, the few seeds from accidental pollination of the best flowers were kept for the following season, These seeds produced even bigger and better plants than the year before and seed collection was performed as before. The third season, most of the plants were not as large or desirable as the second season, but there were many good individuals. Seed collection and cultivation the fourth season resulted in plants inferior even to the first crop, and this trend continued year after year. What went wrong? The grower collected seed from the best plants each year and grew them under the same conditions. The crop improved the first year. Why did the strain degenerate?
This example illustrates the unconscious selection for undesirable traits. The hypothetical cultivator began well by selecting the best seeds available and growing them properly. The seeds selected for the second season resulted from random hybrid pollinations by early-flowering or overlooked staminate plants and by hermaphrodite pistillate plants. Many of these random pollen-parents may be undesirable for breeding since they may pass on tendencies toward premature maturation, retarded maturation, or hermaphrodism. However, the collected hybrid seeds produce, on the average, larger and more desirable offspring than the first season. This condition is called hybrid vigor and results from the hybrid crossing of two diverse gene pools. The tendency is for many of the dominant characteristics from both parents to be transmitted to the F1 offspring, resulting in particularly large and vigorous plants. This increased vigor due to recombination of dominant genes often raises the cannabinoid level of the F1 offspring, but hybridization also opens up the possibility that undesirable (usually recessive) genes may form pairs and express their characteristics in the F2 offspring. Hybrid vigor may also mask inferior qualities due to abnormally rapid growth. During the second season, random pollinations again accounted for a few seeds and these were collected. This selection draws on a huge gene pool and the possible F2 combinations are tremendous. By the third season the gene pool is tending toward early-maturing plants that are accli matized to their new conditions instead of the bud producing conditions of their native environment. These acclimatized members of the third crop have a higher chance of maturing viable seeds than the parental types, and random pollinations will again increase the numbers of acclimatized individuals, and thereby increase the chance that undesirable characteristics associated with acclimatization will be transmitted to the next F2 generation. This effect is compounded from generation to generation and finally results in a fully acclimatized weed strain of little value.
With some care the breeder can avoid these hidden dangers of unconscious selection. Definite goals are vital to progress in breeding Cannabis. What qualities are desired in a strain that it does not already exhibit? What characteristics does a strain exhibit that are unfavorable and should be bred out? Answers to these questions suggest goals for breeding. In addition to a basic knowledge of Cannabis botany, propagation, and genetics, the successful breeder also becomes aware of the most minute differences and similarities in phenotype. A sensitive rapport is established between breeder and plants and at the same time strict guidelines are followed. A simplified explanation of the time-tested principles of plant breeding shows how this works in practice.
Selection is the first and most important step in the breeding of any plant. The work of the great breeder and plant wizard Luther Burbank stands as a beacon to breeders of exotic strains. His success in improving hundreds of flower, fruit, and vegetable crops was the result of his meticulous selection of parents from hundreds of thousands of seedlings and adults from the world over.
Bear in mind that in the production of any new plant, selection plays the all-important part. First, one must get clearly in mind the kind of plant he wants, then breed and select to that end always choosing through a series of years the plants which are approaching nearest the ideal, and rejecting all others. -Luther Burbank (in James, 1964)
Proper selection of prospective parents is only possible if the breeder is familiar with the variable characteristics of Cannabis that may be genetically controlled, has a way to accurately measure these variations, and has established goals for improving these characteristics by selective breeding. A detailed list of variable traits of Cannabis, including parameters of variation for each trait and comments pertaining to selective breeding for or against it, are found at the end of this chapter. By selecting against unfavorable traits while selecting for favorable ones, the unconscious breeding of poor strains is avoided.
The most important part of Burbank’s message on selection tells breeders to choose the plants “which are approaching nearest the ideal,” and REJECT ALL OTHERS! Random pollinations do not allow the control needed to reject the undesirable parents. Any staminate plant that survives detection and roguing (removal from the population), or any stray staminate branch on a pistillate hermaphrodite may become a pollen parent for the next generation. Pollination must be controlled so that only the pollen- and seed-parents that have been carefully selected for favorable traits will give rise to the next generation.
Selection is greatly improved if one has a large sample to choose from! The best plant picked from a group of 10 has far less chance of being significantly different from its fellow seedlings than the best plant selected from a sample of 100,000. Burbank often made his initial selections of parents from samples of up to 500,000 seedlings. Difficulties arise for many breeders because they lack the space to keep enough examples of each strain to allow a significant selection. A Cannabis breeder’s goals are restricted by the amount of space available. Formulating a well defined goal lowers the number of individuals needed to perform effective crosses. Another technique used by breeders since the time of Burbank is to make early selections. Seedling plants take up much less space than adults. Thousands of seeds can be germinated in a flat. A flat takes up the same space as a hundred 10-centimeter (4-inch) sprouts or sixteen 30-centimeter (12-inch) seedlings or one 60-centimeter (24-inch) juvenile. An adult plant can easily take up as much space as a hundred flats. Simple arithmetic shows that as many as 10,000 sprouts can be screened in the space required by each mature plant, provided enough seeds are available. Seeds of rare strains are quite valuable and exotic; however, careful selection applied to thousands of individuals, even of such common strains as those from Colombia or Mexico, may produce better offspring than plants from a rare strain where there is little or no opportunity for selection after germination. This does not mean that rare strains are not valuable, but careful selection is even more important to successful breeding. The random pollinations that produce the seeds in most imported marijuana assure a hybrid condition which results in great seedling diversity. Distinctive plants are not hard to discover if the seedling sample is large enough.
Traits considered desirable when breeding Cannabis often involve the yield and quality of the final product, but these characteristics can only be accurately measured after the plant has been harvested and long after it is possible to select or breed it. Early seedling selection, therefore, only works for the most basic traits. These are selected first, and later selections focus on the most desirable characteristics exhibited by juvenile or adult plants. Early traits often give clues to mature phenotypic expression, and criteria for effective early seedling selection are easy to establish. As an example, particularly tall and thin seedlings might prove to be good parents for pulp or fiber production, while seedlings of short internode length and compound branching may be more suitable for flower production. However, many important traits to be selected for in Cannabis floral clusters cannot be judged until long after the parents are gone, so many crosses are made early and selection of seeds made at a later date.
Hybridization is the process of mixing differing gene pools to produce offspring of great genetic variation from which distinctive individuals can be selected. The wind performs random hybridization in nature. Under cultivation, breeders take over to produce specific, controlled hybrids. This process is also known as cross-pollination, cross-fertilization, or simply crossing. If seeds result, they will produce hybrid offspring exhibiting some characteristics from each parent.
Large amounts of hybrid seed are most easily pro duced by planting two strains side by side, removing the staininate plants of the seed strain, and allowing nature to take its course. Pollen- or seed-sterile strains could be developed for the production of large amounts of hybrid seed without the labor of thinning; however, genes for sterility are rare. It is important to remember that parental weak nesses are transmitted to offspring as well as strengths. Because of this, the most vigorous, healthy plants are always used for hybrid crosses.
Also, sports (plants or parts of plants carrying and expressing spontaneous mutations) most easily transmit mutant genes to the offspring if they are used as pollen parents. If the parents represent diverse gene pools, hybrid vigor results, because dominant genes tend to carry valuable traits and the differing dominant genes inherited from each parent mask recessive traits inherited from the other. This gives rise to particularly large, healthy individuals. To increase hybrid vigor in offspring, parents of different geographic origins are selected since they will probably represent more diverse gene pools.
Occasionally hybrid offspring will prove inferior to both parents, but the first generation may still contain recessive genes for a favorable characteristic seen in a parent if the parent was homozygous for that trait. First generation (F1) hybrids are therefore inbred to allow recessive genes to recombine and express the desired parental trait. Many breeders stop with the first cross and never realize the genetic potential of their strain. They fail to produce an F2 generation by crossing or self-pollinating F1 offspring. Since most domestic Cannabis strains are F1 hybrids for many characteristics, great diversity and recessive recombination can result from inbreeding domestic hybrid strains. In this way the breeding of the F1 hybrids has afready been accomplished, and a year is saved by going directly to F2 hybrids. These F2 hybrids are more likely to express recessive parental traits. From the F2 hybrid generation selections can be made for parents which are used to start new true-breeding strains. Indeed, F2 hybrids might appear with more extreme characteristics than either of the P~ parents. (For example, P1 high-THC X P1 low-THC yields F1 hybrids of intermediate THC content. Selfing the F1 yields F2 hybrids, of both P1 [high and low THC] phenotypes, intermediate F1 phenotypes, and extra-high THC as well as extra-low THC phenotypes.)
Also, as a result of gene recombination, F1 hybrids are not true-breeding and must be reproduced from the original parental strains. When breeders create hybrids they try to produce enough seeds to last for several successive years of cultivation, After initial field tests, undesirable hybrid seeds are destroyed and desirable hybrid seeds stored for later use. If hybrids are to be reproduced, a clone is saved from each parental plant to preserve original parental genes.
Back-crossing is another technique used to produce offspring with reinforced parental characteristics. In this case, a cross is made between one of the F~ or subsequent offspring and either of the parents expressing the desired trait. Once again this provides a chance for recombination and possible expression of the selected parental trait. Backcrossing is a valuable way of producing new strains, but it is often difficult because Cannabis is an annual, so special care is taken to save parental stock for back-crossing the following year. Indoor lighting or greenhouses can be used to protect breeding stock from winter weather. In tropical areas plants may live outside all year. In addition to saving particular parents, a successful breeder always saves many seeds from the original P1 group that produced the valuable characteristic so that other P1 plants also exhibiting the characteristic can be grown and selected for back-crossing at a later time.
Several types of breeding are summarized as follows:
1 – Crossing two varieties having outstanding qualities (hybridization).
2 – Crossing individuals from the F1 generation or selfing F1 individuals to realize the possibilities of the original cross (differentiation).
3 – Back crossing to establish original parental types.
4 – Crossing two similar true-breeding (homozygous) varieties to preserve a mutual trait and restore vigor.
It should be noted that a hybrid plant is not usually hybrid for all characteristics nor does a true-breeding strain breed true for all characteristics. When discussing crosses, we are talking about the inheritance of one or a few traits only. The strain may be true-breeding for only a few traits, hybrid for the rest. Monohybrid crosses involve one trait, dihybrid crosses involve two traits, and so forth. Plants have certain limits of growth, and breeding can only produce a plant that is an expression of some gene already present in the total gene pool. Nothing is actually created by breeding; it is merely the recombination of existing genes into new genotypes. But the possibilities of recombination are nearly limitless.
The most common use of hybridization is to cross two outstanding varieties. Hybrids can be produced by crossing selected individuals from different high-potency strains of different origins, such as Thailand and Mexico. These two parents may share only the characteristic of high psychoactivity and differ in nearly every other respect. From thisgreat exchange of genes many phenotypes may appear in the F2 generation. From these offspring the breeder selects individuals that express the best characteristics of the parents. As an example, consider some of the offspring from the P1 (parental) cross: Mexico X Thailand. In this case, genes for high THC content are selected from both parents while other desirable characteristics can be selected from either one. Genes for large stature and early maturation are selected from the Mexican seed-parent, and genes for large calyx size and sweet floral aroma are selected from the Thai pollen parent. Many of the F1 offspring exhibit several of the desired characteristics. To further promote gene segregation, the plants most nearly approaching the ideal are crossed among themselves. The F2 generation is a great source of variation and recessive expression. In the F2 generation there are several individuals out of many that exhibit all five of the selected characteristics. Now the process of inbreeding begins, using the desirable F2 parents.
If possible, two or more separate lines are started, never allowing them to interbreed. In this case one acceptable staminate plant is selected along with two pistillate plants (or vice versa). Crosses between the pollen parent and the two seed parents result in two lines of inheritance with slightly differing genetics, but each expressing the desired characteristics. Each generation will produce new, more acceptable combinations.
If two inbred strains are crossed, F1 hybrids will be less variable than if two hybrid strains are crossed. This comes from limiting the diversity of the gene pools in the two strains to be hybridized through previous inbreeding. Further independent selection and inbreeding of the best plants for several generations will establish two strains which are true-breeding for all the originally selected traits. This means that all the offspring from any parents in the strain will give rise to seedlings which all exhibit the selected traits. Successive inbreeding may by this time have resulted in steady decline in the vigor of the strain.
When lack of vigor interferes with selecting phenotypes for size and hardiness, the two separately selected strains can then be interbred to recombine nonselected genes and restore vigor. This will probably not interfere with breeding for the selected traits unless two different gene systems control the same trait in the two separate lines, and this is highly unlikely. Now the breeder has produced a hybrid strain that breeds true for large size, early maturation, large sweet-smelling calyxes, and high THC level. The goal has been reached!
Wind pollination and dioecious sexuality favor a heterozygous gene pool in Cannabis. Through Anbreeding, hybrids are adapted from a heterozygous gene pool to a homozygous gene pool, providing the genetic stability needed to create true-breeding strains. Establishing pure strains enables the breeder to make hybrid crosses with a better chance of predicting the outcome. Hybrids can be created that are not reproducible in the F2 generation. Commercial strains of seeds could be developed that would have to be purchased each year, because the F1 hybrids of two pure-bred lines do not breed true. Thus, a seed breeder can protect the investment in the results of breeding, since it would be nearly impossible to reproduce the parents from F2 seeds.
At this time it seems unlikely that a plant patent would be awarded for a pure-breeding strain of Cannabis. In the future, however, with the legalization of cultivation, it is a certainty that corporations with the time, space, and money to produce pure and hybrid strains of Cannabis will apply for patents. It may be legal to grow only certain patented strains produced by large seed companies. Will this be how government and industry combine to control the quality and quantity of Cannabis?
Much of the breeding effort of North American cultivators is concerned with acclimatizing high-THC strains of equatorial origin to the climate of their growing area while preserving potency. Late-maturing, slow, and irregularly flowering strains like those of Thailand have difficulty maturing in many parts of North America. Even ~:n a greenhouse, it may not be possible to mature plants to their full native potential.
To develop an early-maturing and rapidly flowering strain, a breeder may hybridize as in the previous example. However, if it is important to preserve unique imported genetics, hybridizing may be inadvisable. Alternatively, a pure cross is made between two or more Thai plants that most closely approach the ideal in blooming early. At this point the breeder may ignore many other traits and aim at breeding an earlier-maturing variety of a pure Thai strain. This strain may still mature considerably later than is ideal for the particular location unless selective pressure is exerted. If further crosses are made with several individuals that satisfy other criteria such as high THC content, these may be used to develop another pure Thai strain of high THC content. After these true-breeding lines have been established, a dihybrid pure cross can be made in an attempt to produce an F1 generation containing early maturing, high-THC strains of pure Thai genetics, in other words, an acclimatized bud strain.
Crosses made without a clear goal in mind lead to strains that acclimatize while losing many favorable characteristics. A successful breeder is careful not to overlook a characteristic that may prove useful. It is imperative that original imported Cannabis genetics be preserved intact to protect the species from loss of genetic variety through excessive hybridization. A currently unrecognized gene may be responsible for controlling resistance to a pest or disease, and it may only be possible to breed for this gene by back crossing existing strains to original parental gene pools.
Once pure breeding lines have been established, plant breeders classify and statistically analyze the offspring to determine the patterns of inheritance for that trait. This is the system used by Gregor Mendel to formulate the basic laws of inheritance and aid the modern breeder in predict ing the outcome of crosses
1 – Two pure lines of Cannabis that differ in a particular trait are located.
2 – These two pure-breeding lines are crossed to produce an F1 generation.
3 – The F1 generation is inbred.
4 – The offspring of the F1 and F2 generations are classified with regard to the trait being studied.
5 – The results are analyzed statistically.
6 – The results are compared to known patterns of inheritance so the nature of the genes being selected for can be characterized.
Fixing traits (producing homozygous offspring) in Cannabis strains is more difficult than it is in many other flowering plants. With monoecious strains or hermaphrodites it is possible to fix traits by self-pollinating an individual exhibiting favorable traits. In this case one plant acts as both mother and father. However, most strains of Cannabis are dioecious, and unless hermaphroditic reactions can be induced, another parent exhibiting the trait is required to fix the trait. If this is not possible, the unique individual may be crossed with a plant not exhibiting the trait, inbred in the F1 generation, and selections of parents exhibiting the favorable trait made from the F2 generation, but this is very difficult.
If a trait is needed for development of a dioecious strain it might first be discovered in a monoecious strain and then fixed through selfing and selecting homozygous offspring. Dioecious individuals can then be selected from the monoecious population and these individuals crossed to breed out monoecism in subsequent generations.
Galoch (1978) indicated that gibberellic acid (GA3) promoted stamen production while indoleacetic acid (IAA),ethrel, and kinetin promoted pistil production in prefloral dioecious Cannabis. Sex alteration has several useful applications. Most importantly, if only one parent expressing a desirable trait can be found, it is difficult to perform a cross unless it happens to be a hermaphrodite plant. Hormones might be used to change the sex of a cutting from the desirable plant, and this cutting used to mate with it This is most easily accomplished by changing a pistillate cutting to a staminate (pollen) parent, using a spray of 100 ppm gibberellic acid in water each day for five consecutive days. Within two weeks staminate flowers may appear. Pollen can then be collected for selfing with the original pistillate parent. Offspring from the cross should also be mostly pistillate since the breeder is selfing for pistillate sexuality. Staminate parents reversed to pistillate floral production make inferior seed-parents since few pistillate flowers and seeds are formed.
If entire crops could be manipulated early in life to produce all pistillate or staminate plants, seed production and seedless Cannabis production would be greatly facilitated.
Sex reversal for breeding can also be accomplished by mutilation and by photoperiod alteration. A well-rooted, flourishing cutting from the parent plant is pruned back to 25% of its original size and stripped of all its remaining flowers. New growth will appear within a few days, and several flowers of reversed sexual type often appear. Flowers of the unwanted sex are removed until the cutting is needed for fertilization. Extremely short light cycles (6-8 hour photoperiod) can also cause sex reversal. However, this process takes longer and is much more difficult to perform in the field.
Genotype and Phenotype Ratios
It must be remembered, in attempting to fix favorable characteristics, that a monohybrid cross gives rise to four possible recombinant genotypes, a dihybrid cross gives rise to 16 possible recombinant genotypes, and so forth.
Phenotype and genotype ratios are probabilistic. If recessive genes are desired for three traits it is not effective to raise only 64 offspring and count on getting one homozygous recessive individual. To increase the probability of success it is better to raise hundreds of offspring, choosing only the best homozygous recessive individuals as future parents. All laws of inheritance are based on chance and offspring may not approach predicted ratios until many more have been phenotypically characterized and grouped than the theoretical minimums.
The genotype of each individual is expressed by a mosaic of thousands of subtle overlapping traits. It is the sum total of these traits that determines the general phenotype of an individual. It is often difficult to determine if the characteristic being selected is one trait or the blending of several traits and whether these traits are controlled by one or several pairs of genes. It often makes little difference that a breeder does not have plants that are proven to breed true. Breeding goals can still be established. The selfing of F1 hybrids will often give rise to the variation needed in the F2 generation for selecting parents for subsequent generations, even if the characteristics of the original parents of the F1 hybrid are not known. It is in the following generations that fixed characteristics appear and the breeding of pure strains can begin. By selecting and crossing individuals that most nearly approach the ideal described by the breeding goals, the variety can be continuously improved even if the exact patterns of inheritance are never determined. Complementary traits are eventually combined into one line whose seeds reproduce the favorable parental traits. Inbreeding strains also allows weak recessive traits to express themselves and these abnormalities must be diligently removed from the breeding population. After five or six generations, strains become amazingly uniform. Vigor is occasionally restored by crossing with other lines or by backcrossing.
Parental plants are selected which most nearly approach the ideal. If a desirable trait is not expressed by the parent, it is much less likely to appear in the offspring. It is imperative that desirable characteristics be hereditary and not primarily the result of environment and cultivation. Acquired traits are not hereditary and cannot be made hereditary. Breeding for as few traits as possible at one time greatly increases the chance of success. In addition to the specific traits chosen as the aims of breeding, parents are selected which possess other generally desirable traits such as vigor and size. Determinations of dominance and recessiveness can only be made by observing the outcome of many crosses, although wild traits often tend to be dominant. This is one of the keys to adaptive survival. However, all the possible combinations will appear in the F2 generation if it is large enough, regardless of dominance.
Now, after further simplifying this wonderful system of inheritance, there are additional exceptions to the rules which must be explored. In some cases, a pair of genes may control a trait but a second or third pair of genes is needed to express this trait. This is known as gene interaction. No particular genetic attribute in which we may be interested is totally isolated from other genes and the effects of environment. Genes are occasionally transferred in groups instead of assorting independently. This is known as gene linkage, These genes are spaced along the same chromosome and may or may not control the same trait. The result of linkage might be that one trait cannot be inherited without another. At times, traits are associated with the X and Y sex chromosomes and they may be limited to expression in only one sex (sex linkage). Crossing over also interferes with the analysis of crosses. Crossing over is the exchanging of entire pieces of genetic material between two chromosomes. This can result in two genes that are normally linked appearing on separate chromosomes where they will be independently inherited. All of these processes can cause crosses to deviate from the expected Mendelian outcome. Chance is a major factor in breeding Cannabis, or any introduced plant, and the more crosses a breeder attempts the higher are the chances of success.
Variate, isolate, intermate, evaluate, multiplicate, and disseminate are the key words in plant improvement. A plant breeder begins by producing or collecting various prospective parents from which the most desirable ones are selected and isolated. Intermating of the select parents results in offspring which must be evaluated for favorable characteristics. If evaluation indicates that the offspring are not improved, then the process is repeated. Improved off spring are multiplied and disseminated for commercial use. Further evaluation in the field is necessary to check for uniformity and to choose parents for further intermating. This cyclic approach provides a balanced system of plant improvement.
The basic nature of Cannabis makes it challenging to breed. Wind pollination and dioecious sexuality, which account for the great adaptability in Cannabis, cause many problems in breeding, but none of these are insurmountable. Developing a knowledge and feel for the plant is more important than memorizing Mendelian ratios. The words of the great Luther Burbank say it well, “Heredity is indelibly fixed by repetition.”
The first set of traits concerns Cannabis plants as a whole while the remainder concern the qualities of seedlings, leaves, fibers, and flowers. Finally a list of various Cannabis strains is provided along with specific characteristics. Following this order, basic and then specific selections of favorable characteristics can be made. List of Favorable Traits of Cannabis in Which Variation Occurs
1. General Traits
a) Size and Yield – The size of an individual Cannabis plant is determined by environmental factors such as room for root and shoot growth, adequate light and nutrients, and proper irrigation. These environmental factors influence the phenotypic image of genotype, but the genotype of the individual is responsible for overall variations in gross morphology, including size. Grown under the same conditions, particularly large and small individuals are easily spotted and selected. Many dwarf Cannabis plants have been reported and dwarfism may be subject to genetic control, as it is in many higher plants, such as dwarf corn and citrus. Cannabis parents selected for large size tend to produce offspring of a larger average size each year. Hybrid crosses between tall (Cannabis sativa-Mexico) strains and short (Cannabis ruderalis-Russia) strains yield F1 offspring of intermediate height (Beutler and der Marderosian 1978). Hybrid vigor, however, will influence the size of offspring more than any other genetic factor. The increased size of hybrid offspring is often amazing and accounts for much of the success of Cannabis cultivators in raising large plants. It is not known whether there is a set of genes for “gigantism” in Cannabis or whether polyploid individuals really yield more than diploid due to increased chromosome count. Tetraploids tend to be taller and their water requirements are often higher than diploids. Yield is determined by the overall production of fiber, seed, or resin and selective breeding can be used to increase the yield of any one of these products. However, several of these traits may be closely related, and it may be impossible to breed for one without the other (gene linkage). Inbreeding of a pure strain increases yield only if high yield parents are selected. High yield plants, staminate or pistillate, are not finally selected until the plants are dried and manicured. Because of this, many of the most vigorous plants are crossed and seeds selected after harvest when the yield can be measured.
b) Vigor – Large size is often also a sign of healthy vigorous growth. A plant that begins to grow immediately will usually reach a larger size and produce a higher yield in a short growing season than a sluggish, slow-growing plant. Parents are always selected for rich green foliage and rapid, responsive growth. This will ensure that genes for certain weaknesses in overall growth and development are bred out of the population while genes for strength and vigor remain..
c) Adaptability – It is important for a plant with a wide distribution such as Cannabis to be adaptable to many different environmental conditions. Indeed, Cannabis is one of the most genotypically diverse and phenotypically plastic plants on earth; as a result it has adapted to environmental conditions ranging from equatorial to temperate climates. Domestic agricultural circumstances also dictate that Cannabis must be grown under a great variety of conditions. Plants to be selected for adaptability are cloned and grown in several locations. The parental stocks with the highest survival percentages can be selected as prospective parents for an adaptable strain. Adaptability is really just another term for hardiness under varying growth conditions.
d) Hardiness – The hardiness of a plant is its overall resistance to heat and frost, drought and overwatering, and so on. Plants with a particular resistance appear when adverse conditions lead to the death of the rest of a large population. The surviving few members of the population might carry inheritable resistance to the environmental factor that destroyed the majority of the population. Breeding these survivors, subjecting the offspring to continuing stress conditions, and selecting carefully for several generations should result in a pure-breeding strain with increased resistance to drought, frost, or excessive heat.
e) Disease and Pest Resistance – In much the same way as for hardiness a strain may be bred for resistance to a certain disease, such as damping-off fungus. If flats of seedlings are infected by damping-off disease and nearly all of them die, the remaining few will have some resistance to damping-off fungus. If this resistance is inheritable, it can be passed on to subsequent generations by crossing these surviving plants. Subsequent crossing, tested by inoculating flats of seedling offspring with damping-off fungus, should yield a more resistant strain.
Resistance to pest attack works in much the same way. It is common to find stands of Cannabis where one or a few plants are infested with insects while adjacent plants are untouched. Cannabinoid and terpenoid resins are most probably responsible for repelling insect attack, and levels of these vary from plant to plant. Cannabis has evolved defenses against insect attack in the form of resin-secreting glandular trichomes, which cover the reproductive and associated vegetative structures of mature plants. Insects, finding the resin disagreeable, rarely attack mature Cannabis flowers. However, they may strip the outer leaves of the same plant because these develop fewer glandular trichomes and protective resins than the flowers. Nonglandular cannabinoids and other compounds produced within leaf and stem tissues which possibly inhibit insect attack, may account for the varying resistance of seedlings and vegetative juvenile plants to pest infestation. With the popularity of greenhouse Cannabis cultivation, a strain is needed with increased resistance to mold, mite, aphid,- or white fly infestation. These problems are often so severe that greenhouse cultivators destroy any plants which are attacked. Molds usually reproduce by wind-borne spores, so negligence can rapidly lead to epidemic disaster. Selection and breeding of the least infected plants should result in strains with increased resistance.
f) Maturation – Control of the maturation of Cannabis is very important no matter what the reason for growing it. If Cannabis is to be grown for fiber it is important that the maximum fiber content of the crop be reached early and that all of the individuals in the crop mature at the same time to facilitate commercial harvesting. Seed production requires the even maturation of both pollen and seed parents to ensure even setting and maturation of seeds. An uneven maturation of seeds would mean that some seeds would drop and be lost while others are still ripening. An understanding of floral maturation is the key to the production of high quality Cannabis. Changes in gross morphology are accompanied by changes in cannabinoid and terpenoid production and serve as visual keys to determining the ripeness of Cannabis flowers.
A Cannabis plant may mature either early or late, be fast or slow to flower, and ripen either evenly or sequentially.
Breeding for early or late maturation is certainly a reality; it is also possible to breed for fast or slow flowering and even or sequential ripening. In general, crosses between early-maturing plants give rise to early-maturing offspring, crosses between late-maturing plants give rise to late maturing offspring, and crosses between late- and early maturing plants give rise to offspring of intermediate maturation. This seems to indicate that maturation of Cannabis is not controlled by the simple dominance and recessiveness of one gene but probably results from incomplete dominance and a combination of genes for separate aspects of maturation. For instance, Sorghum maturation is controlled by four separate genes. The sum of these genes produces a certain phenotype for maturation. Although breeders do not know the action of each specific gene, they still can breed for the total of these traits and achieve results more nearly approaching the goal of timely maturation than the parental strains.
g) Root Production – The size and shape of Cannabis root systems vary greatly. Although every embryo sends out a taproot from which lateral roots grow, the individual growth pattern and final size and shape of the roots vary considerably. Some plants send out a deep taproot, up to 1 meter (39 inches) long, which helps support the plant against winds and rain. Most Cannabis plants, however, produce a poor taproot which rarely extends more than 30 centimeters (1 foot). Lateral growth is responsible for most of the roots in Cannabis plants. These fine lateral roots offer the plant additional support but their primary function is to absorb water and nutrients from the soil. A large root system will be able to feed and support a large plant. Most lateral roots grow near the surface of the soil where there is more water, more oxygen, and more available nutrients. Breeding for root size and shape may prove beneficial for the production of large rain- and wind resistant strains. Often Cannabis plants, even very large ones, have very small and sensitive root systems. Recently, certain alkaloids have been discovered in the roots of Cannabis that might have some medical value. If this proves the case, Cannabis may be cultivated and bred for high alkaloid levels in the roots to be used in the commercial production of pharmaceuticals. As with many traits, it is difficult to make selections for root types until the parents are harvested. Because of this many crosses are made early and seeds selected later.
h) Branching – The branching pattern of a Cannabis plant is determined by the frequency of nodes along each branch and the extent of branching at each node. For examples, consider a tall, thin plant with slender limbs made up of long internodes and nodes with little branching (Oaxaca, Mexico strain). Compare this with a stout, densely branched plant with limbs of short internodes and highly branched nodes (Hindu Kush hashish strains). Different branching patterns are preferred for the different agricultural applications of fiber, flower, or resin production. Tall, thin plants with long internodes and no branching are best adapted to fiber production; a short, broad plant with short internodes and well developed branching is best adapted to floral production. Branching structure is selected that will tolerate heavy rains and high winds without breaking. This is quite advantageous to outdoor growers in temperate zones with short seasons. Some breeders select tall, limber plants (Mexico) which bend in the wind; others select short, stiff plants (Hindu Kush) which resist the weight of water without bending.
i) Sex – Attempts to breed offspring of only one sexual type have led to more misunderstanding than any otherfacet of Cannabis genetics. The discoveries of McPhee (1925) and Schaffner (1928) showed that pure sexual type and hermaphrodite conditions are inherited and that the percentage of sexual types could be altered by crossing with certain hermaphrodites. Since then it has generally been assumed by researchers and breeders that a cross between ANY unselected hermaphrodite plant and a pistillate seed-parent should result in a population of all pistillate offspring. This is not the case. In most cases, the offspring of hermaphrodite parents tend toward hermaphrodism, which is largely unfavorable for the production of Cannabis other than fiber hemp. This is not to say that there is no tendency for hermaphrodite crosses to alter sex ratios in the offspring. The accidental release of some pollen fro predominantly pistillate hermaphrodites, along with the complete eradication of nearly every staminate and staminate hermaphrodite plant may have led to a shift in sexual ratio in domestic populations of sinsemilla Cannabis. It is commonly observed that these strains tend toward 60% to 80% pistillate plants and a few pistillate hermaphrodites are not uncommon in these populations.
However, a cross can be made which will produce nearly all pistillate or staminate individuals. If the proper pistillate hermaphrodite plant is selected as the pollen parent and a pure pistillate plant is selected as the seed parent it is possible to produce an F1, and subsequent generations, of nearly all pistillate offspring. The proper pistillate hermaphrodite pollen-parent is one which has grown as a pure pistillate plant and at the end of the season, or under artificial environmental stress, begins to develop a very few staminate flowers. If pollen from these few staminate flowers forming on a pistillate plant is applied to a pure pistillate seed parent, the resulting F1 generation should be almost all pistillate with only a few pistillate hermaphrodites. This will also be the case if the selected pistillate hermaphrodite pollen source is selfed and bears its own seeds. Remember that a selfed hermaphrodite gives rise to more hermaphrodites, but a selfed pistillate plant that has given rise to a limited number of staminate flowers in response to environmental stresses should give rise to nearly all pistillate offspring. The F1 offspring may have a slight tendency to produce a few staminate flowers under further environmental stress and these are used to produce F2 seed. A monoecious strain produces 95+% plants with many pistillate and staminate flowers, but a dioecious strain produces 95+% pure pistillate or staminate plants. A plant from a dioecious strain with a few intersexual flowers is a pistillate or staminate hermaphrodite. Therefore, the difference between monoecism and hermaphrodism is one of degree, determined by genetics and environment.
Crosses may also be performed to produce nearly all staminate offspring. This is accomplished by crossing a pure staminate plant with a staminate plant that has produced a few pistillate flowers due to environmental stress, or selfing the latter plant. It is readily apparent that in the wild this is not a likely possibility. Very few staminate plants live long enough to produce pistillate flowers, and when this does happen the number of seeds produced is limited to the few pistillate flowers that occur. In the case of a pistillate hermaphrodite, it may produce only a few staminate flowers, but each of these may produce thou sands of pollen grains, any one of which may fertilize one of the plentiful pistillate flowers, producing a seed. This is another reason that natural Cannabis populations tend toward predominantly pistillate and pistillate hermaphrodite plants. Artificial hermaphrodites can be produced by hormone sprays, mutilation, and altered light cycles. These should prove most useful for fixing traits and sexual type. Drug strains are selected for strong dioecious tendencies. Some breeders select strains with a sex ratio more nearly approaching one than a strain with a high pistillate sex ratio. They believe this reduces the chances of pistillate plants turning hermaphrodite later in the season.
2. Seedling Traits
Seedling traits can be very useful in the efficient and purposeful selection of future parental stock. If accurateselection can be exercised on small seedlings, much larger populations can be grown for initial selection, as less space is required to raise small seedlings than mature plants. Whorled phyllotaxy and resistance to damping-off are two traits that may be selected just after emergence of the embryo from the soil. Early selection for vigor, hardiness, resistance, and general growth form may be made when the seedlings are from 30 to 90 centimeters (1 to 3 feet) tall. Leaf type, height, and branching are other criteria for early selection. These early-selected plants cannot be bred until they mature, but selection is the primary and most important step in plant improvement. Whorled phyllotaxy is associated with subsequent anomalies in the growth cycle (i.e., multiple leaflets and flattened or clubbed stems). Also, most whorled plants are staminate and whorled phyllotaxy may be sex-linked.
3. Leaf Traits
Leaf traits vary greatly from strain to strain. In addition to these regularly occurring variations in leaves, there are a number of mutations and possible traits in leaf shape. It may turn out that leaf shape is correlated with other traits in Cannabis. Broad leaflets might be associated with a low calyx-to-leaf ratio and narrow leaflets might be associated with a high calyx-to-leaf ratio. If this is the case, early selection of seedlings by leaflet shape could determine the character of the flowering clusters at harvest. Both compound and webbed leaf variations seem to be hereditary, as are general leaf characteristics. A breeder may wish to develop a unique leaf shape for an ornamental strain or increase leaf yield for pulp production.
A peculiar leaf mutation was reported from an F1 Colombian plant in which two leaves on the plant, at the time of flowering, developed floral clusters of 5-10 pistillate calyxes at the intersection of the leaflet array and the petiole attachment, on the adaxial (top) side of the leaf. One of these clusters developed a partial staminate flower but fertilization was unsuccessful. It is unknown if this mutation is hereditary. From Afghanistan, another example has been observed with several small floral clusters along the petioles of many of the large primary leaves.
4. Fiber Traits
More advanced breeding has occurred in fiber strains than any other type of Cannabis. Over the years many strains have been developed with improved maturation, increased fiber content, and improved fiber quality as regards length, strength, and suppleness. Extensive breeding programs have been carried on in France, Italy, Russia, and the United States to develop better varieties of fiber Cannabis. Tall limbless strains that are monoecious are most desirable. Monoeciousness is favored, because in dioecious populations the staminate plants will mature first and the fibers will become brittle before the pistillate plants are ready for harvest. The fiber strains of Europe are divided into northern and southern varieties. The latter require higher temperatures and a longer vegetative period and as a result grow taller and yield more fiber.
5. Floral Traits
Many individual traits determine the floral charactistics of Cannabis This section will focus on the individual traits of pistillate floral clusters with occasional comments about similar traits in staminate floral clusters. Pistillate flowering clusters are the seed-producing organs of Cannabis; they remain on the plant and go through many changes that cannot be compared to staminate plants.
a) Shape – The basic shape of a floral cluster is determined by the internode lengths along the main floral axis and within individual floral clusters. Dense, long clusters result when internodes are short along a long floral axis and there are short internodes within the individual compact floral clusters (Hindu Kush). Airy clusters result when a plant forms a stretched floral axis with long internodes between well-branched individual floral clusters (Thailand).
The shape of a floral cluster is also determined by the general growth habit of the plant. Among domestic Cannabis phenotypes, for instance, it is obvious that floral clusters from a creeper phenotype plant will curve upwards at the end, and floral clusters from the huge upright phenotype will have long, straight floral clusters of various shapes.Early in the winter, many strains begin to stretch and cease calyx production in preparation for rejuvenation and subsequent vegetative growth in the spring. Staminate plants also exhibit variation in floral clusters. Some plants have tight clusters of staminate calyxes resembling inverted grapes (Hindu Kush) and others have long, hanging groups of flowers on long, exposed, leafless branches (Thailand).
b) Form – The form of a floral cluster is determined by the numbers and relative proportions of calyxes and flowers. A leafy floral cluster might be 70% leaves and have a calyx-to-leaf ratio of 1-to-4. It is obvious that strains with a high calyx-to-leaf ratio are more adapted to calyx production, and therefore, to resin production. This factor could be advantageous in characterizing plants as future parents of bud strains. At this point it must be noted that pistillate floral clusters are made up of a number of distinct parts. They include stems, occasional seeds, calyxes, inner leaves subtending calyx pairs (small, resinous, 1-3 leaflets), and outer leaves subtending entire floral clusters (larger, little resin, 3-11 leaflets). The ratios (by dry weight) of these various portions vary by strain, degree of pollination, and maturity of the floral clusters. Maturation is a reaction to environmental change, and the degree of maturity reached is subject to climatic limits as well as breeder’s preference. Because of this interplay between environment and genetics in the control of floral form it is often difficultto breed Cannabis for floral characteristics. A thorough knowledge of the way a strain matures is important in separating possible inherited traits of floral clusters from acquired traits. Chapter IV, Maturation and Harvesting of Cannabis, delves into the secrets and theories of maturation. For now, we will assume that the following traits are described from fully mature floral clusters (peak floralstage) before any decline.
c) Calyx Size – Mature calyxes range in size from 2 to 12 millimeters (1/16 to 3/8 inch) in length. Calyx size is largely dependent upon age and maturity. Calyx size of a floral cluster is best expressed as the average length of the mature viable calyxes. Calyxes are still considered viable if both pistils appear fresh and have not begun to curl or change colors. At this time, the calyx is relatively straight and has not begun to swell with resin and change shape as it will when the pistils die. It is generally agreed that the production of large calyxes is often as important in determining the psychoactivity of a strain as the quantity of calyxes produced. Hindu Kush, Thai, and Mexican strains are some of the most psychoactive strains, and they are often characterized by large calyxes and seeds. Calyx size appears to be an inherited trait in Cannabis. Completely acclimatized hybrid strains usually have many rather small calyxes, while imported strains with large calyxes retain that size when inbred. Initial selection of large seeds increases the chance that offspring will be of the large-calyx variety. Aberrant calyx development occasionally results in double or fused calyxes, both of which may set seed. This phenomenon is most pronounced in strains from Thailand and India.
d) Color – The perception and interpretation of color in Cannabis floral clusters is heavily influenced by the imagination of the cultivator or breeder. A gold strain does not appear metallic any more than a red strain resembles a fire engine. Cannabis floral clusters are basically green, but changes may take place later in the season which alter the color to include various shades. The intense green of chlorophyll usually masks the color of accessory pigments, Chlorophyll tends to break down late in the season and anthocyanin pigments also contained in the tissues are unmasked and allowed to show through. Purple, resulting from anthocyanin accumulation, is the most common color in living Cannabis, other than green. This color modification is usually triggered by seasonal change, much as the leaves of many deciduous trees change color in the fall. This does not mean, however, that expression of color is controlled by environment alone and is not an inheritable trait. For purple color to develop upon maturation, a strain must have the genetically controlled metabolic potential to produce anthocyanin pigments coupled with a responsiveness to environmental change such that anthocyanin pigments are unmasked and become visible. This also means that a strain could have the genes for expression of purple color but the color might never be expressed if the environmental conditions did not trigger anthocyanin pigmentation or chlorophyll breakdown. Colombian and Hindu Kush strains often develop purple coloration year after year when subjected to low night temperatures during maturation. Color changes will be discussed in more detail in Chapter IV Maturation and Harvesting of Cannabis.
Carotenoid pigments are largely responsible for the yellow, orange, red, and brown colors of Cannabis. They also begin to show in the leaves and calyxes of certain strains as the masking green chlorophyll color fades upon maturation. Gold strains are those which tend to reveal underlying yellow and orange pigments as they mature. Red strains are usually closer to reddish brown in color, although certain carotenoid and anthocyanin pigments are nearly red and localized streaks of these colors occasionally appear in the petioles of very old floral clusters. Red color in pressed, imported tops is often a result of masses of reddish brown dried pistils.
Several different portions of floral cluster anatomy may change colors, and it is possible that different genes may control the coloring of these various parts.
The petioles, adaxial (top) surfaces, and abaxial (bottom) surfaces of leaves, as well as the stems, calyxes, and pistils color differently in various strains. Since most of the outer leaves are removed during manicuring, the color expressed by the calyxes and inner leaves during the late flowering stages will be all that remains in the final product. This is why strains are only considered to be truly purple or gold if the calyxes maintain those colors when dried. Anthocyanin accumulation in the stems is sometimes considered a sign of phosphorus deficiency but in most situations results from unharmful excesses of phosphorus or it is a genetic trait. Also, cold temperatures might interfere with phosphorus uptake resulting in a deficiency. Pistils in Hindu Kush strains are quite often magenta or pink in color when they first appear. They are viable at this time and turn reddish brown when they wither, as in most strains. Purple coloration usually indicates that pistillate plants are over-mature and cannabinoid biosynthesis is slowing down during cold autumn weather.
e) Cannabinoid Level – Breeding Cannabis for cannabinoid level has been accomplished by both licensed legitimate and clandestine researchers. Warmke (1942) and Warmke and Davidson (1943-44) showed that they could significantly raise or lower the cannabinoid level by selective breeding. Small (1975a) has divided genus Cannabis into four distinct chemotypes based on the relative amounts of THC and CBD. Recent research has shown that crosses between high THC: low CBD strains and low THC: high CBD strains yield offspring of cannabinoid content intermediate between the two parents. Beutler and der Marderosian (1978) analyzed the F1 offspring of the controlled cross C. Sativa (Mexico-high THC) X C. ruderalis (Russia-low THC) and found that they fell into two groups intermediate between the parents in THC level. This indicates that THC production is most likely controlled by more than one gene. Also the F1 hybrids of lower THC (resembling the staminate parent) were twice as frequent as the higher THC hybrids (resembling the pistillate parent). More re search is needed to learn if THC production in Cannabis is associated with the sexual type of the high THC parent or if high THC characteristics are recessive. According to Small (1979) the cannabinoid ratios of strains grown in northern climates are a reflection of the cannabinoid ratio of the pure, imported, parental strain. This indicates that cannabinoid phenotype is genetically controlled, and the levels of the total cannabinoids are determined by environment. Complex highs produced by various strains of Cannabis may be blended by careful breeding to produce hybrids of varying psychoactivity, but the level of total psychoactivity is dependent on environment. This is also the telltale indication that unconscious breeding with un desirable low-THC parents could rapidly lead to the degeneration rather than improvement of a bud strain. It is ob vious that individuals of fiber strains are of little if any use in breeding bud strains.
Breeding for cannabinoid content and the eventual characterization of varying highs produced by Cannabis is totally subjective guesswork without the aid of modern analysis techniques. A chromatographic analysis system would allow the selection of specific cannabinoid types, especially staminate pollen parents. Selection of staminate parents always presents a problem when breeding for cannabinoid content. Staminate plants usually express the same ratios of cannabinoids as their pistiliate counterparts but in much lower quantities, and they are rarely allowed to reach full maturity for fear of seeding the pistillate portion of the crop. A simple bioassay for THC content of staminate plants is performed by leaving a series of from three to five numbered bags of leaves and tops of various prospective pollen parents along with some rolling papers in several locations frequented by a steady repeating crowd of marijuana smokers. The bag completely consumed first can be considered the most desirable to smoke and possibly the most psychoactive. It would be impossible for one per son to objectively select the most psychoactive staminate plant since variation in the cannabinoid profile is subtle. The bioassay reported here is in effect an unstructured panel evaluation which averages the opinions of unbiased testers who are exposed to only a few choices at a time. Such bioassay results can enter into selecting the staminate parent.
It is difficult to say how many genes might control THC-acid synthesis. Genetic control of the biosynthetic pathway could occur at many points through the action of enzymes controlling each individual reaction. It is generally accepted that bud strains have an enzyme system which quickly converts CBD-acid to THC-acid, favoring THC-acid accumulation. Fiber strains lack this enzyme activity, so CBD-acid accumulalion is favored since there is little conversion to THC-acid. These same enzyme systems are probably also sensitive to changes in heat and light.
It is supposed that variations in the type of high associated with different strains of Cannabis result from vary ing levels of cannabinoids. THC is the primary psycho active ingredient which is acted upon synergistically by small amounts of CBN, CBD, and other accessory cannabi noids. Terpenes and other aromatic constituents of Canna bis might also potentiate or suppress the effect of THC. We know that cannabinoid levels may be used to establish cannabinoid phenotypes and that these phenotypes are passed on from parent to offspring. Therefore, cannabinoid levels are in part determined by genes. To accurately characterize highs from various individuals and establish criteria for breeding strains with particular cannabinoid contents, an accurate and easy method is needed for measuring cannabinoid levels in prospective parents. Inheritance and expression of cannabinoid chemotype is certainly complex.
f) Taste and Aroma – Taste and aroma are closely linked. As our senses for differentiating taste and aroma are connected, so are the sources of taste and aroma in Cannabis. Aroma is produced primarily by aromatic terpenes produced as components of the resin secreted by glandular trichomes on the surface of the calyxes and subtending leaflets. When a floral cluster is squeezed, the resinous heads of glandular trichomes rupture and the aromatic terpenes are exposed to the air. There is often a large difference between the aroma of fresh and dry floral clusters This is explained by the polymerization (joining together in a chain) of many of the smaller molecules of aromatic ter penes to form different aromatic and nonaromatic terpene polymers. This happens as Cannabis resins age and mature, both while the plant is growing and while curing after harvest. Additional aromas may interfere with the primary terpenoid components, such as ammonia gas and other gaseous products given off by the curing, fermentation or spoilage of the tissue (non-resin) portion of the floral clusters.
A combination of at least twenty aromatic terpenes (103 are known to occur in Cannabis) and other aromatic compounds control the aroma of each plant. The production of each aromatic compound may be influenced by many genes; therefore, it is a complex matter to breed Cannabis for aroma. Breeders of perfume roses often are amazed at the complexity of the genetic control of aroma,Each strain, however, has several characteristic aromas, and these are occasionally transmitted to hybrid offspring such that they resemble one or both parents in aroma. Manytimes breeders complain that their strain has lost the desired aromatic characteristics of the parental strains. Fixed hybrid strains will develop a characteristic aroma that is hereditary and often true-breeding. The cultivator with preservation of a particular aroma as a goal can clone the individual with a desired aroma in addition to breeding it. This is good insurance in case the aroma is lost in the off spring by segregation and recombination of genes.
The aromas of fresh or dried clusters are sampled and compared in such a way that they are separated to avoid confusion. Each sample is placed in the corner of a twice folded, labeled piece of unscented writing paper at room temperature (above 650). A light squeeze will release the aromatic principles contained within the resin exuded by the ruptured glandular trichome head. When sampling, never squeeze a floral cluster directly, as the resins will adhere to the fingers and bias further sampling. The folded paper conveniently holds the floral cluster, avoids confusion during sampling, and contains the aromas as a glass does in wine tasting.
Taste is easily sampled by loosely rolling dried floral clusters in a cigarette paper and inhaling to draw a taste across the tongue. Samples should be approximately the same size.
Taste in Cannabis is divided into three categories according to usage: the taste of the aromatic components carried by air that passes over the Cannabis when it is inhaled without being lighted; the taste of the smoke from burning Cannabis; and the taste of Cannabis when it is consumed orally. These three are separate entities.
The terpenes contained in a taste of unlighted Cannabis are the same as those sensed in the aroma, but perceived through the sense of taste instead of smell. Orally ingested Cannabis generally tastes bitter due to the vegetative plant tissues, but the resin is characteristically spicy and hot, somewhat like cinnamon or pepper. The taste of Cannabis smoke is determined by the burning tissues and vaporizing terpenes. These terpenes may not be detected in the aroma and unlighted taste.
Biosynthetic relationships between terpenes and cannabinoids have been firmly established. Indeed, cannabinoids are synthesized within the plant from terpene precursors. It is suspected that changes in aromatic terpene levels parallel changes in cannabinoid levels during maturation. As connections between aroma and psychoactivity are uncovered, the breeder will be better able to make field selections of prospective high-THC parents without complicated analysis.
g) Persistence of Aromatic Principles and Cannabinoids – Cannabis resins deteriorate as they age, and the aromatic principles and cannabinoids break down slowly until they are hardly noticeable. Since fresh Cannabis is only available once a year in temperate regions, an important breeding goal has been a strain that keeps well when packaged. Packageability and shelf life are important considerations in the breeding of fresh fruit species and will prove equally important if trade in Cannabis develops after legalization.
h) Trichome Type – Several types of trichomes are present on the epidermal surfaces of Cannabis. Several of these trichomes are glandular and secretory in nature and are divided into bulbous, capitate sessile, and capitate stalked types. Of these, the capitate stalked glandular trichomes are apparently responsible for the intense secretion of cannabinoid laden resins. Plants with a high density of capitate stalked trichomes are a logical goal for breeders of Cannabis. The number and type of trichomes is easily characterized by observation with a small hand lens (lOX to 50X). Recent research by V. P. Soroka (1979) concludes that a positive correlation exists between the number of glandular trichomes on leaves and calyxes and the various cannabinoid contents of the floral clusters. In other words, many capitate stalked trichomes means higher THC levels.
i) Resin Quantity and Quality – Resin production by the glandular trichomes varies. A strain may have many glandular trichomes but they may not secrete very much resin. Resin color also varies from strain to strain. Resin heads may darken and become more opaque as they mature, as suggested by several authors. Some strains, however, produce fresh resins that are transparent amber instead of clear and colorless, and these are often some of the most psychoactive strains. Transparent resins, regardless of color, are a sign that the plant is actively carrying out resin biosynthesis. When biosynthesis ceases, resins turn opaque as cannabinoid and aromatic levels decline. Resin color is certainly an indication of the conditions inside the resin head, and this may prove to be another important criterion for breeding.
j) Resin Tenacity – For years strains have been bred for hashish production. Hashish is formed from detached resin heads. In modern times it might be feasible to breed a strain with high resin production that gives up its precious covering of resin heads with only moderate shaking, rather than the customary flailing that also breaks up the plant. This would facilitate hashish production. Strains that are bred for use as marijuana would benefit from extremely tenacious resin heads that would not fall off during pacing and shipment.
k) Drying and Curing Rate – The rate and extent to which Cannabis dries is generally determined by the way it is dried, but, all conditions being the same, some strains dry much more rapidly and completely than others. It is assumed that resin has a role in preventing desiccation and high resin content might retard drying. However, it is misconception that resin is secreted to coat and seal the surface of the calyxes and leaves. Resin is secreted by glandular trichomes, but they are trapped under a cuticle layer surrounding the head cells of the trichome holding the resin away from the surface of the leaves. There it would rarely if ever have a chance to seal the surface of the epidermal layer and prevent the transpiration of water. It seems that an alternate reason must be found for the great variations in rate and extent of drying. Strains may be bred that dry and cure rapidly to save valuable time.
1) Ease of Manicuring – One of the most time-consuming aspects of commercial Cannabis production is the seemingly endless chore of manicuring, or removing the larger leaves from the floral clusters. These larger outer leaves are not nearly as psychoactive as the inner leaves and calyxes, so they are usually removed before selling as marijuana. Strains with fewer leaves obviously require less time to manicure. Long petioles on the leaves facilitate removal by hand with a small pair of scissors. If there is a marked size difference between very large outer leaves and tiny, resinous inner leaves it is easier to manicure quickly because it is easier to see which leaves to remove.
m) Seed Characteristics – Seeds may be bred for many characteristics including size, oil content, and protein content. Cannabis seed is a valuable source of drying oils, and Cannabis-seed cake is a fine feed for ranch animals. Higher-protein varieties may be developed for food. Also, seeds are selected for rapid germination rate.
n) Maturation – Cannabis strains differ greatly as to when they mature and how they respond to changing environment. Some strains, such as Mexican and Hindu Kush, are famous for early maturation, and others, such as Colombian and Thai, are stubborn in maturing and nearly always finish late, if at all. Imported strains are usually character ized as either early, average, or late in maturing; however, a particular strain may produce some individuals which mature early and others which mature late. Through selection, breeders have, on the one hand, developed strains that mature in four weeks, outdoors under temperate condi tions; and on the other hand, they have developed greenhouse strains that mature in up to four months in their protected environment. Early maturation is extremely advantageous to growers who live in areas of late spring and early fall freezes. Consequently, especially early-maturing plants are selected as parents for future early-maturing strains.
o) Flowering – Once a plant matures and begins to bear flowers it may reach peak floral production in a few weeks, or the floral clusters may continue to grow and develop for several months. The rate at which a strain flowers is independent of the rate at which it matures, so a plant may wait until late in the season to flower and then grow extensive, mature floral clusters in only a few weeks.
p) Ripening – Ripening of Cannabis flowers is the final step in their maturation process Floral clusters will usually mature and ripen in rapid succession, but sometimes large floral clusters will form and only after a period of apparent hesitation will the flowers begin to produce resin and ripen. Once ripening starts it usually spreads over the entire plant, but some strains, such as those from Thailand, are known to ripen a few floral clusters at a time over several months. Some fruit trees are similarly everbearing with a yearlong season of production. Possibly Cannabis strains could be bred that are true everbearing perennials that continue to flower and mature consistently all year long.
q) Cannabinoid Profile – It is supposed that variations in the type of high associated with different strains of Cannabis result from varying levels of cannabinoids. THC is the primary psychoactive ingredient which is acted upon synergistically by small amounts of CBN, CBD, and other accessory cannabinoids. We know that cannabinoid levels may be used to establish cannabinoid phenotypes and that these phenotypes are passed on from parent to offspring. Therefore, cannabinoid levels are in part determined by genes. To accurately characterize highs from various individuals and establish criteria for breeding strains with particular cannabinoid contents, an accurate and easy method is necessary for measuring cannabinoid levels in prospective parents. Various combinations of these traits are possible and inevitable. The traits that we most often see are most likely dominant and any effort to alter genetics and improve Cannabis strains are most easily accomplished by concentrating on the major phenotypes for the most important traits. The best breeders set high goals of a limited scope and adhere to their ideals.
6. Gross Phenotypes of Cannabis Strains
The gross phenotype or general growth form is determined by size, root production, branching pattern, sex, maturation, and floral characteristics. Most imported varieties have characteristic gross phenotypes although there tend to be occasional rare examples of almost every phenotype in nearly every variety. This indicates the complexity of genetic control determining gross phenotype. Hybrid crosses between imported pure varieties were the beginning of nearly every domestic strain of Cannabis. In hybrid crosses, some dominant characteristics from each parental variety are exhibited in various combinations by the F1 offspring. Nearly all of the offspring will resemble both parents and very few will resemble only one parent. This sounds like it is saying a lot, but this F1 hybrid generation is far from true-breeding and the subsequent F2 generation will exhibit great variation, tending to look more like one or the other of the original imported parental varieties, and will also exhibit recessive traits not apparent in either of the original parents. If the F1 offspring are desirable plants it will be difficult to continue the hybrid traits in subsequent generations. Enough of the original F1 hybrid seeds are produced so they may be used year after year to produce uniform crops of desirable plants.
Phenotypes and Characteristics of Imported Strains
Following is a list of gross phenotypes and characteristics for many imported strains of Cannabis.
1. Fiber Strain Gross Phenotypes
Fiber strains are characterized as tall, rapidly maturing, limbless plants which are often monoecious. This growth habit has been selected by generations of fiberproducing farmers to facilitate forming long fibers through even growth and maturation. Monoecious strains mature more evenly than dioecious strains, and fiber crops are usually not grown long enough to set seed which interferes with fiber production. Most varieties of fiber Cannabis originate in the northern temperate climates of Europe, Japan, China and North America. Several strains have been selected from the prime hemp growing areas and offered commercially over the last fifty years in both Europe and America. Escaped fiber strains of the midwestern United States are usually tall, skinny, relatively poorly branched, weakly flowered, and low in cannabinoid production. They represent an escaped race of Cannabis sativa hemp. Most fiber strains contain CBD as the primary cannabinoid a little if any THC.
2. Drug Strain Gross Phenotypes
Drug strains are characterized by Delta1-THC as the primary cannabinoid, with low levels of other accessory cannabinoids such as THCV, CBD, CBC, and CBN. This resultsfrom selective breeding for high potency or natural selection in niches where Delta1-THC biosynthesis favors survival.
a) Colombia – (0 to 10 north latitude)
Colombian Cannabis originally could be divided into two basic strains: one from the low-altitude humid coastal areas along the Atlantic near Panama, and the other from the more arid mountain areas inland from Santa Marta. More recently, new areas of cultivation in the interior plateau of southern central Colombia and the highland valleys stretching southward from the Atlantic coast have become the primary areas of commercial export Cannabis cultivation. Until recent years high quality Cannabis was available through the black market from both coastal and highland Colombia. Cannabis was introduced to Colombia just over 100 years ago, and its cultivation is deeply rooted in tradition. Cultivation techniques often involve transplanting of selected seedlings and other individual attention. The production of “la mona amarilla” or gold buds is achieved by girdling or removing a strip of bark from the main stem of a nearly mature plant, thereby restricting the flow of water, nutrients, and plant products. Over several days the leaves dry up and fall off as the flowers slowly die and turn yellow. This produces the highly prized “Colombian gold” so prevalent in the early to middle 1970s (Partridge 1973). Trade names such as “punta roja” (red tips [pistils] ), “Cali Hills,” “choco,” “lowland,” “Santa Marta gold,” and “purple” give us some idea of the color of older varieties and the location of cultivation.
In response to an incredible demand by America for Cannabis, and the fairly effective control of Mexican Cannabis importation and cultivation through tightening border security and the use of Paraquat, Colombian farmers have geared up their operations. Most of the marijuana smoked in America is imported from Colombia. This also means that the largest number of seeds available for domestic cultivation also originate in Colombia. Cannabis agri-business has squeezed out all but a few small areas where labor-intensive cultivation of high quality Cannabis such as “Ia mona amarilla” can continue. The fine marijuana of Colombia was often seedless, but commercial grades are nearly always well seeded. As a rule today, the more remote highland areas are the centers of commercial agriculture and few of the small farmers remain. It is thought that some highland farmers must still grow fine Cannabis, and occasional connoisseur crops surface. The older seeds from the legendary Colombian strains are now highly prized by breeders. In the heyday of “Colombian gold” this fine cerebral marijuana was grown high in the mountains. Humid lowland marijuana was characterized by stringy, brown, fibrous floral clusters of sedative narcotic high. Now highland marijuana has become the commercial product and is characterized by leafy brown floral clusters and sedative effect. Many of the unfavorable characteristics of imported Colombian Cannabis result from hurried commercial agricultural techniques combined with poor curingand storage. Colombian seeds still contain genes favoring vigorous growth and high THC production. Colombian strains also contain high levels of CBD and CBN, which could account for sedative highs and result from poor curing and storage techniques. Domestic Colombian strains usually lack CBD and CBN. The commercial Cannabis market has brought about the eradication of some local strains by hybridizing with commercial strains.
Colombian strains appear as relatively highly branched conical plants with a long upright central stem, horizontal limbs and relatively short internodes. The leaves are characterized by highly serrated slender leaflets (7-11) in a nearly complete to overlapping circular array of varying shades of medium green. Colombian strains usually flower late in temperate regions of the northern hemisphere and may fail to mature flowers in colder climates. These strains favor the long equatorial growing seasons and often seem insensitive to the rapidly decreasing daylength during autumn in temperate latitudes. Because of the horizon tal branching pattern of Colombian strains and their long growth cycle, pistillate plants tend to produce many flow ering clusters along the entire length of the stem back to the central stalk. The small flowers tend to produce small, round, dark, mottled, and brown seeds. Imported and domestic Colombian Cannabis often tend to be more sedative in psychoactivity than other strains. This may be caused by the synergistic effect of THC with higher levels of CBD or CBN. Poor curing techniques on the part of Colombian farmers, such as sun drying in huge piles resembling compost heaps, may form CBN as a degradation product of THC. Colombian strains tend to make excellent hybrids with more rapidly maturing strains such as those from Central and North America.
b) Congo – (5 north to 5 south latitude)
Most seeds are collected from shipments of commercial grade seeded floral clusters appearing in Europe.
c) Hindu Kush Range – Cannabis indica (Afghanistan and Pakistan) – (30 to 37 north latitude)
This strain from the foothills (up to 3,200 meters [10,000 feetj) of the Hindu Kush range is grown in small used primarily for the production of hashish. In these areas hashish is usually made from the resins covering the pistil late calyxes and associated leaflets. These resins are removed by shaking and crushing the flowering tops over a silk screen and collecting the dusty resins that fall off the plants. Adulteration and pressing usually follow in the production of commercial hashish. Strains from this area are often used as type examples for Cannabis indica. Early maturation and the belief by clandestine cultivators that this strain may be exempt from laws controlling Cannabis sativa and indeed may be legal, has resulted in its prolifera tion throughout domestic populations of Cannabis. Names such as “hash plant” and “skunk weed” typify its acrid aroma reminiscent of “primo” hashish from the high valleys near Mazar-i-Sharif, Chitral, and Kandahar in Afghanistan and Pakistan.
This strain is characterized by short, broad plants with thick, brittle woody stems and short internodes. The main stalk is usually only four to six feet tall, but the relatively unbranched primary limbs usually grow in an upright fashion until they are nearly as tall as the central stalk and form a sort of upside-down conical shape. These strains are of medium size, with dark green leaves having 5 to 9 ve wide, coarsely serrated leaflets in a circular array. The lower leaf surface is often lighter in color than the upp surface. These leaves have so few broad coarse leaflets that they are often compared to a maple leaf. Floral clusters are dense and appear along the entire length of the primary limbs as very resinous leafy balls. Most plants produce flowering clusters with a low calyx-to-leaf ratio, but the inner leaves associated with the calyxes are usually liberally encrusted with resin. Early maturation and extreme resin production is characteristic of these strains. This may be the result of acclimatization to northern temperate latitudes and selection for hashish production. The acrid smell associated with strains from the Hindu Kush appears very early in the seedling stage of both staminate and pistillate individuals and continues throughout the life of the plant. Sweet aromas do often develop but this strain usually loses the sweet fragrance early, along with the clear, cerebral psychoactivity.
Short stature, early maturation, and high resin production make Hindu Kush strains very desirable for hybridizing and indeed they have met with great popularity. The gene pool of imported Hindu Kush strains seems to be dominant for these desirable characteristics and they seem readily passed on to the F1 hybrid generation. A fine hybrid may result from crossing a Hindu Kush variety with a late-maturing, tall, sweet strain from Thailand, India, or Nepal. This produces hybrid offspring of short stature, high resin content, early maturation, and sweet taste that will mature high quality flowers in northern climates. Many hybrid crosses of this type are made each year and are currently cultivated in many areas of North America.Hindu Kush seeds are usually large, round, and dark grey or black in coloring with some mottling.
d) India Centra1 Southern – Kerala, Mysore, and Madras regions (10 to 20 north latitude)
Ganja (or flowering Cannabis tops) has been grown in India for hundreds of years. These strains are usually grown in a seedless fashion and are cured, dried, and smoked as marijuana instead of being converted to hashish as in many Central Asian areas. This makes them of considerable interest to domestic Cannabis cultivators wishing to reap the benefits of years of selective breeding for fine ganja by Indian farmers. Many Europeans and Americans now live in these areas of India and ganja strains are finding their way into domestic American Cannabis crops.
Ganja strains are often tall and broad with a central stalk up to 12 feet tall and spreading highly-branched limbs. The leaves are medium green and made up of 7 to 11 leaflets of moderate size and serration arranged in a circular array. The frond-like limbs of ganja strains result from extensive compound branching so that by the time floral clusters form they grow from tertiary or quaternary limbs. This promotes a high yield of floral clusters which in ganja strains tend to be small, slender, and curved. Seeds are usually small and dark. Many spicy aromas and tastes occur in Indian ganja strains and they are extremely resinous and psychoactive. Medicinal Cannabis of the late 1800s and early 1900s was usually Indian ganja.
e) Jamaica – (18 north latitude)
Jamaican strains were not uncommon in the late 1960s and early 1970s but they are much rarer today. Both green and brown varieties are grown in Jamaica. The top-of-the-line seedless smoke is known as the “lamb’s bread” and is rarely seen outside Jamaica. Most purported Jamaican strains appear stringy and brown much like lowland or commercial Colombian strains. Jamaica’s close proximity to Colombia and its position along the routes of marijuana smuggling from Colombia to Florida make it likely that Colombian varieties now predominate in Jamaica even if these varieties were not responsible for the original Jamaican strains. Jamaican strains resemble Colombian strains in leaf shape, seed type and general morphology but they tend to be a little taller, thinner, and lighter green. Jamaican strains produce a psychoactive effect of a particularly clear and cerebral nature, unlike many Colombian strains. Some strains may also have come to Jamaica from the Caribbean coast of Mexico, and this may account for the introduction of cerebral green strains.
f) Kenya – Kisumu (5 north to 5 south latitude)
Strains from this area have thin leaves and vary in color from light to dark green. They are characterized by cerebral psychoactivity and sweet taste. Hermaphrodites are common.
g) Lebanon – (34 north latitude)
Lebanese strains are rare in domestic Cannabis crops but do appear from time to time. They are relatively short and slender with thick stems, poorly developed limbs, and wide, medium-green leaves with 5 to 11 slightly broad leaflets. They are often early-maturing and seem to be quite leafy, reflecting a low calyx-to-leaf ratio. The calyxes are relatively large and the seeds flattened, ovoid and dark brown in color. As with Hindu Kush strains, these plants are grown for the production of screened and pressed hashish, and the calyx-to-leaf ratio may be less important than the total resin production for hashish making. Lebanese strains resemble Hindu Kush varieties in many ways and it is likely that they are related.
h) Malawi, Africa – (10 to 15 south latitude)
Malawi is a small country in eastern central Africa bordering Lake Nyasa. Over the past few years Cannabis from Malawi has appeared wrapped in bark and rolled tightly, approximately four ounces at a time. The near seedless flowers are spicy in taste and powerfully psychoactive. Enthusiastic American and European Cannabis cultivators immediately planted the new strain and it has become incorporated into several domestic hybrid strains. They appear as a dark green, large plant of medium height and strong limb growth. The leaves are dark green with coarsely serrated, large, slender leaflets arranged in a narrow, drooping, hand-like array. The leaves usually lackserrations on the distal (tip portion) 20% of each leaflet. The mature floral clusters are sometimes airy, resulting from long internodes, and are made up of large calyxes and relatively few leaves. The large calyxes are very sweet and resinous, as well as extremely psychoactive. Seeds are large, shortened, flattened, and ovoid in shape with a dark grey or reddish brown, mottled perianth or seed coat. The caruncle or point of attachment at the base of the seed is uncommonly deep and usually is surrounded by a sharpedged lip. Some individuals turn a very light yellow green in the flowering clusters as they mature under exposed conditions. Although they mature relatively late, they do seem to have met with acceptance in Great Britain and North America as bud strains. Seeds of many strains appear in small batches of low-quality African marijuana easily available in Amsterdam and other European cities. Phenotypes vary considerably, however, many are similar in appearance to strains from Thailand.
i) Mexico – (15 to 27 north latitude)
Mexico had long been the major source of marijuana smoked in America until recent years. Efforts by the border patrols to stop the flow of Mexican marijuana into the United States were only minimally effective and many varieties of high quality Mexican Cannabis were continually available. Many of the hybrid strains grown domestically today originated in the mountains of Mexico. In recent years, however, the Mexican government (with monetary backing by the United States) began an intensive program to eradicate Cannabis through the aerial spraying of herbicides such as Paraquat. Their program was effective, and high quality Mexican Cannabis is now rarely available. It is ironic that the NIMH (National Institute of Mental Health) is using domestic Mexican Cannabis strains grown in Mississippi as the pharmaceutical research product for chemotherapy and glaucoma patients. In the prime of Mexican marijuana cultivation from the early 1960s to the middle 1970s, strains or “brands” of Cannabis were usually affixed with the name of the state or area where they were grown. Hence names like “Chiapan,” “Guerreran,” “Nayarit,” “Michoacan,” “Oaxacan,” and “Sinaloan” have geographic origins behind their common names and mean something to this very day. All of these areas are Pacific coastal states extending in order from Sinaloa in the north at 27; through Nayarit, Jalisco, Michoacan, Guerrero, and Oaxaca; to Chiapas in the south at 15 – All of these states stretch from the coast into the mountains where Cannabis is grown.
Strains from Michoacan, Guerrero, and Oaxaca were the most common and a few comments may be ventured about each and about Mexican strains in general.
Mexican strains are thought of as tall, upright plants of moderate to large size with light to dark green, large leaves. The leaves are made up of long, medium width, moderately serrated leaflets arranged in a circular array. The plants mature relatively early in comparison to strains from Colombia or Thailand and produce many long floral clusters with a high calyx-to-leaf ratio and highly cerebral psychoactivity. Michoacan strains tend to have very slender leaves and a very high calyx-to-leaf ratio as do Guerreran strains, but Oaxacan strains tend to be broader-leafed, often with leafier floral clusters. Oaxacan strains are generally the largest and grow vigorously, while Michoacan strains are smaller and more delicate. Guerreran strains are often short and develop long, upright lower limbs. Seeds from most Mexican strains are fairly large, ovoid, and slightly flattened with a light colored grey or brown, unmottled perianth. Smaller, darker, more mottled seeds have appeared in Mexican marijuana during recent years. This may indicate that hybridization is taking place in Mexico, possibly with introduced seed from the largest seed source in the world, Colombia. No commercial seeded Cannabis crops are free from hybridization and great variation may occur in the offspring. More recently, large amounts of hybrid domestic seed have been introduced into Mexico. It is not uncommon to find Thai and Afghani phenotypes in recent shipments of Cannabis from Mexico.
j) Morocco, Rif Mountains – (35 north latitude)
The Rif mountains are located in northernmost Morocco near the Mediterranean Sea and range up to 2,500 meters (8,000 feet). On a high plateau surrounding the city of Ketama grows most of the Cannabis used forkif floral clusters and hashish production. Seeds are broadsown or scattered on rocky terraced fields in the spring, as soon as the last light snows melt, and the mature plants are harvested in late August and September. Mature plants are usually 1 to 2 meters (4 to 6 feet) tall and only slightly branched. This results from crowded cultivation techniques and lack of irrigation. Each pistillate plant bears only one main terminal flower cluster full of seeds. Few staminate plants, if any, are pulled to prevent pollination. Although Cannabis in Morocco was originally cultivated for floral clusters to be mixed with tobacco and smoked as kif, hashish production has begun in the past 30 years due to Western influence. In Morocco, hashish is manufactured by shaking the entire plant over a silk screen and collecting the powdery resins that pass through the screen. It is a matter of speculation whether the original Moroccan kif strains might be extinct. It is reported that some of these strains were grown for seedless flower production and areasof Morocco may still exist where this is the tradition.
Because of selection for hashish production, Moroccan strains resemble both Lebanese and Hindu Kush strains in their relatively broad leaves, short growth habit, and highresin production. Moroccan strains are possibly related to these other Cannabis indica types.
k) Nepal – (26 to 30 north latitude)
Most Cannabis in Nepal occurs in wild stands high in the Himalayan foothills (up to 3,200 meters [10,000 feet]). Little Cannabis is cultivated, and it is from select wild plants that most Nepalese hashish and marijuana originate. Nepalese plants are usually tall and thin with long, slightly branched limbs. The long, thin flowering tops are very aromatic and reminiscent of the finest fresh “temple ball” and “finger” hashish hand-rubbed from wild plants. Resin production is abundant and psychoactivity is high Few Nepalese strains have appeared in domestic Cannabis crops but they do seem to make strong hybrids with strains from domestic sources and Thailand.
I) Russian – (35 to 60 north latitude) Cannabis ruderalis (uncultivated)
Short stature (10 to 50 centimeters [3 to 18 inches]) and brief life cycle (8 to 10 weeks), wide, reduced leaves and specialized seeds characterize weed Cannabis of Russia. Janischewsky (1924) discovered weedy Cannabis and named it Cannabis ruderalis. Ruderalis could prove valuable in breeding rapidly maturing strains for commercial use in temperate latitudes. It flowers when approximately 7 weeksold without apparent dependence on daylength. Russian Cannabis ruderalis is nearly always high in CBD and low in THC.
m) South Africa – (22 to 35 south latitude)
Dagga of South Africa is highly acclaimed. Most seeds have been collected from marijuana shipments in Europe. Some are very early-maturing (September in northern latitudes) and sweet smelling. The stretched light green floral clusters and sweet aroma are comparable to Thai strains.
n) Southeast Asia – Cambodia, Laos, Thailand and Vietnam (10 to 20 north latitude)
Since American troops first returned from the war in Vietnam, the Cambodian, Laotian, Thai, and Vietnamese strains have been regarded as some of the very finest in the world. Currently most Southeast Asian Cannabis is pro duced in northern and eastern Thailand. Until recent times, Cannabis farming has been a cottage industry of the northern mountain areas and each family grew a small garden. The pride of a farmer in his crop was reflected in the high quality and seedless nature of each carefully wrapped Thai stick. Due largely to the craving of Americans for exotic marijuana, Cannabis cultivation has become a big business in Thailand and many farmers are growing large fields of lower quality Cannabis in the eastern lowlands. It is suspected that other Cannabis strains, brought to Thailand to replenish local strains and begin large plantations, may have hybridized with original Thai strains and altered the resultant genetics. Also, wild stands of Cannabis may now be cut and dried for export.
Strains from Thailand are characterized by tall meandering growth of the main stalk and limbs and fairly extensive branching. The leaves are often very large with 9 to 11 long, slender, coarsely serrated leaflets arranged in a droop ing hand like array. The Thai refer to them as “alligator tails” and the name is certainly appropriate.
Most Thai strains are very late-maturing and subject to hermaphrodism. It is not understood whether strains from Thailand turn hermaphrodite as a reaction to the extremes of northern temperate weather or if they have a genetically controlled tendency towards hermaphrodism. To the dismay of many cultivators and researchers, Thai strains mature late, flower slowly, and ripen unevenly. Retarded floral development and apparent disregard for changes in photoperiod and weather may have given rise to the story that Cannabis plants in Thailand live and bear flowers for years. Despite these shortcomings, Thai strains are very psychoactive and many hybrid crosses have been made with rapidly maturing strains, such as Mexican andHindu Kush, in a successful attempt to create earlymaturing hybrids of high psychoactivity and characteristic Thai sweet, citrus taste. The calyxes of Thai strains are very large, as are the seeds and other anatomical features, leading to the misconception that strains may be polyploid. No natural polyploidy has been discovered in any strains of Cannabis though no one has ever taken the time to look thoroughly. The seeds are very large, ovoid, slightly flattened, and light brown or tan in color. The perianth is never mottled or striped except at the base. Greenhouses prove to be the best way to mature stubborn Thai strains in temperate climes.
3. Hybrid Drug Phenotypes
a) Creeper Phenotype – This phenotype has appeared in several domestic Cannabis crops and it is a frequent phenotype in certain hybrid strains. It has not yet been determined whether this trait is genetically controlled (domi nant or recessive), but efforts to develop a true-breeding strain of creepers are meeting with partial success. This phenotype appears when the main stalk of the seedling has grown to about 1 meter (3 feet) in height. It then begins to bend at approximately the middle of the stalk, up to 700 from the vertical, usually in the direction of the sun. Sub sequently, the first limbs sag until they touch the ground and begin to grow back up. In extremely loose mulch and humid conditions the limbs will occasionally root along the bottom surface. Possibly as a result of increased light expo sure, the primary limbs continue to branch once or twice, creating wide frond-like limbs of buds resembling South Indian strains. This phenotype usually produces very high flower yields. The leaves of these creeper phenotype plants are nearly always of medium size with 7-11 long, narrow, highly serrated leaflets.
b) Huge Upright Phenotype – This phenotype is characterized by medium size leaves with narrow, highly serrated leaflets much like the creeper strains, and may also be an acclimatized North American phenotype. In this phenotype, however, a long, straight central stalk from 2 to 4 meters (6.5 to 13 feet) tall forms and the long, slender primary limbs grow in an upright fashion until they are nearly as tall or occasionally taller than the central stalk. This strain resembles the Hindu Kush strains in general shape, except that the entire domestic plant is much larger than the Hindu Kush with long, slender, more highly branched primary limbs, much narrower leaflets, and a higher calyx-to-leaf ratio. These huge upright strains are also hybrids of many different imported strains and no specific origin may be determined.
The preceding has been a listing of gross phenotypes for several of the many strains of Cannabis occurring worldwide. Although many of them are rare, the seeds appear occasionally due to the extreme mobility of American and European Cannabis enthusiasts. As a consequence of this extreme mobility, it is feared that many of the world’s finest strains of Cannabis have been or may be lost forever due to hybridization with foreign Cannabis populations and the socio-economic displacement of Cannabis cultures worldwide. Collectors and breeders are needed to preserve these rare and endangered gene pools before it is too late. Various combinations of these traits are possible and inevitable. The traits that we most often see are most likely dominant and the improvement of Cannabis strains through breeding is most easily accomplished by concentrating on the dominant phenotypes for the most important traits. The best breeders set high goals of limited scope and adhere to their ideals.