Chapter 16: Breeding

Marijuana Horticulture: The Indoor / Outdoor Medical Grower’s Bible

by Jorge Cervantes

Chimera is without a doubt one of the most dedicated and knowledgeable people working with cannabis today; he brings a passion to cannabis breeding and research not often seen in the industry. Founder of Chimera Seeds, he has produced some excellent varieties of cannabis including ‘C4’, ‘Frostbite’, ‘Calizahr’, and ‘Schnazzleberry’.

Chimera is a well-educated individual, who for years has tried to understand cannabis and how it functions in the brain. This path has seen him through a B Sc. Neuroscience, and post graduate research in the field of Biotechnology and Plant Sciences. He works on the cutting edge of cannabis research, and will certainly bring many new ideas and technologies to cannabis, over the years to come.

I am very pleased to present Chimera’s contribution to this book in the form of this breeding chapter, as he takes the mystery out of breeding and does a great job of simplifying a very complex subject. Thanks, Chimera, for your contributions!

This chapter explains the basic biological processes of sexual propagation in cannabis and the formation of a new generation of seed. Armed with the information in this chapter, any grower will be able to design and begin a rudimentary breeding program and create new generations of seed for future use. These new populations make up a pool of genetic material from which superior individual plants can be selected for production (cloning stock) or for use in breeding programs. It is difficult for small growers to breed better varieties than are available from premium seed companies; however, for the many seed-starved growers who reside in prohibitive societies, making seeds for future us is often a necessity.

Cannabis can be reproduced asexually or sexually. Asexual propagation is more commonly referred to as taking cuttings, or cloning. Branches or growth shoots are removed from chosen donor plants and induced to form roots in a separate medium; these rooted cuttings are then used t plant a uniform crop of genetically identical individuals. Most commercial and many hobby growers propagate their crops asexually to ensure uniformity in growth, yield, and consistency of product in their crops. By planting gardens of genetically identical cuttings from their favorite preselected mother plants, growers are able to maintain an even garden profile, produce a consistent, known quality and quantity from each plant, and expect that all plants will mature at the same time. This ensures the same consistent, quality product from consecutive crops, as long as the same high quality clones are used for each planting. Gardens propagated solely from clones are the most productive and consistent.

Sexual propagation is the process in which male and female sex cells (gametes) from separate parents unite in the female plant to form what will eventually mature into a new, genetically distinct individual. This process occurs when pollen from a male (staminate) parent unites with an ovule within the ovary of a female flower to create an embryo. This embryo, when mature and fully developed, will become a seed.

Each seed is genetically unique and contains some genes from each of its parent plants. Offspring grown from seed are most often different in some way from each other, just as brothers and sisters share some physical qualities of each of their parents, but are rarely identical to their parents or siblings. Because of this variation in plant traits and characters, breeders are able to use sexual reproduction to their advantage by crossing different individuals within a population or family, or hybridizing unrelated lines and subsequently inbreeding the progeny. This results in a phenomenon known as recombination of traits, and it allows breeders the possibility to recover individuals with a combination of the positive traits of both parental lines, all the while selecting plants that do not express the negative aspects. These selected plant stocks are then used as a basis to develop new and improved varieties.

Distinguishing between male (staminate) and female (pistillate) plants is easy. Male plants are distinguished by the appearance of pollen sacks, or anthers, that grow from branch unions. Anthers look similar t a cluster of grapes or a collection of miniature lobster claws growing upwards and inverted from the branch union. Males typically begin to produce these flowers one to four weeks before the females of the same variety, and often bolt, or stretch, when they enter their floral development stage. Females can be distinguished by the development of two whitish hairs, r stigmas, which develop as part f the pistil – the female flower that appears in branch unions or nodes.

Cannabis is an interesting species, in that it is one of the only annual plants that produces each of the male and female sexual organs on different individuals. This is a condition known as dioecy; dioecious plant groups contain individual plants that are either male or female. Dioecy is a hallmark of a cross pollinating species; under normal conditions, cross-pollinated plants (outcrossers) are only able to fertilize other individuals, which has implications we will discuss later.

Although dioecy is most common in cannabis, monoecious varieties do exist. Monoecious varieties produce both staminate and pistillate flowers on the same individual. These monoecious varieties are mainly used for hemp seed production, as they generate the highest yield of seed per acre. Monoecy is not a desirable trait for drug cultivation, where seedless cannabis, or sinsemilla, is sought.

Plants exhibiting both staminate and pistillate flowers are most often referred to as “hermaphrodites” by cannabis cultivators but are more correctly referred too as intersex plants. Intersex plants are a problem for growers who wish to produce seedless cannabis for consumption; just as seedless grapes or oranges are more desirable to consume, the same is true for cannabis. Having to remove the seeds from cannabis flowers prior to consumption is an inconvenience, and burning seeds taste bad and can ruin the smoking or vaporizing experience. We will discuss intersex plants in more detail in this chapter.

The Creation of a Seed

Cannabis is an anemophilous species; this is a fancy way of saying that it is wind-pollinated. Under natural, or wild conditions, male plants undergo dehiscence (shedding of pollen) and disperse vast quantities of pollen into the wind. The pollen travels on air currents and, by chance, lands on the stigma r style f a nearby, or not so nearby, pistillate individual. This is is the pollination event. Because pollen from many species floats in the air, and there is significant chance that pollen from other species will land on a fertile stigma of a waiting female plant, cannabis has evolved recognition systems that ensure only species specific pollen is able to germinate on the style and thus fertilize the female’s ovules. There is physical and biochemical recognition between the pollen grain and the stigmatic surface; together, these insure species identity.

If the biochemical signal is correct and the stigma recognizes the pollen grain as cannabis, the pollen grain is hydrated by a flow of water from the pistil, and it germinates. Just as a seed germinates and sends a taproot into the soil, the pollen grain germinates and sends a pollen tube into the stigma and burrow toward the ovule. Once the tube reaches the ovary, the genetic material carried within pollen is delivered to the ovule, where it is united with the genetic material from the pistillate plant. This fertilization event occurs and creates what is to become an embryo. This embryo grows within a seed coat, and when fully mature in four to five weeks, can be planted and will blossom into a new generation of life.

Making Seeds Step by Step

Step One – Choose breeding parents. Selecting female plants for breeding is a much easier task than selecting males, because female plants readily demonstrate all the traits that are essentially important to a grower, or smoker. The breeder may want to place an emphasis on selecting for potency, flavor, yield, smell, resistance to pests, color, growth stature, etc. Cannabis for consumption is a group of pistillate flowers; a bud is a collection of pistillate flowers; a cola is a group of buds. All a grower has to do is watch these flowers develop over the life cycle, harvest, smoke a bud sample from each plant, and determine the positive characteristics of each plant, for its growth as well as its smoking characteristics. Post harvest evaluation allows additional inspection of aromas and flavors, since these can change as the flower dries and cures.

Choosing male plants with desirable characteristics is not so easy. Males obviously don’t produce female flowers; thus, judging resin content, floral structure, smells, etc., is more of an inferential task – males just don’t demonstrate these characters. Some breeders feel a good method for choosing a potential male is to rub the stem with your finger. The idea is if it exudes a pungent, resinous odor, it may be a good plant. This is really only a crude measure of the odor of the candidate. Although it can be a useful technique, it certainly should not be the major selection criteria.

The best method for determining a potential male’s contribution as a breeding parent is the progeny test. Progeny testing is achieved by taking pollen from a potential breeding male and using it to make seeds with the chosen female(s). The resulting seed population is grown out and examined to determine the effect of the male on the progeny. Progeny tests are without doubt the most reliable method for determining the genetic value of the chosen male as a contributor to the next generation – a concept known as combining ability. One drawback of the progeny test is that it takes time to grow and evaluate the progeny, and the potential male plants must be kept alive if they are to be used again. Sometimes breeders choose to not keep these males alive, only keeping the progeny lots that correspond to the better male plants and destroying the rest. Only the best performing males are allowed to make a genetic contribution to the next generation.

Step Two – Collecting pollen. One branch of male flowers will supply all the pollen necessary fr small scale breeders to produce ample seed for their use. Strip away other branches to guard against accidental random pollination, and to avoid premature pollination, isolate the male as soon as anthers show. Be considerate of the fact that airborne pollen can travel miles. If you brush up against a plant in dehiscence, pollen will become airborne and travel throughout the area.

Just prior to the anther’s opening, place a clean paper or plastic bag ver the branch. Secure the bag at the bottom with a piece of string or a wire tie to prevent pollen from escaping. Keep the bag over the branch for several days to collect pollen. When enough pollen seems to have been collected, tap the branch and shake remaining pollen off into the bag. Carefully remove spent branch and bag so the pollen does not escape.

Step Three – Store and protect pollen (optional). Pollen does not have a long shelf life under natural conditions; it is easily destroyed by high temperatures and moisture. Pollen can, however, be stored in the freezer for several months, if needed. This is accomplished by carefully removing the pollen from the collection bag and subsequently passing it through a screen. This removes any leaf matter from the anthers that may have fallen into the bag and contaminated the pollen, causing it to spoil. Wax paper is placed under the screen, and used to catch the pollen. The pollen can then be collected with a sterile scraper, placed in a small coin envelope or sterile test tube, and placed in the freezer. Cleanliness counts! Pollen should not be repeatedly frozen and thawed, which will decrease its viability.

Step Four – Pollination occurs when pollen comes into contact with the pistil. Depending on variety, fresh pistils are ready to pollinate from two to twelve weeks after flowering is induced. The more pistils on the bud at the time of pollination, the more seed will be produced. Fertile pistils appear turgid and most often are white or off-white in color. Pistils that are withered, rust or brown colored are past the point where successful pollination can occur.

To pollinate, cover the female branch with the pollen filled bag, and briefly shake the bag to ensure the pollen comes into contact with as many pistils as possible. Leave the bag for two days and nights t ensure thorough pollination. Be careful not to scatter pollen when removing the bag, as viable pollen can still become airborne and pollinate nearby plants. If other plants are in the garden and are not intended for pollination, the grower may move target plants from the main grow area into a separate, smaller space for pollination. After a couple of days in the pollen chamber with the males, the female plants are thoroughly sprayed with water to destroy any remaining pollen, before they are moved back into the main grow area where these seeds will mature over the coming weeks. This practice minimizes the possibility of pollen fertilizing the rest of the crop, keeping it seedless as the cultivator requires. To reduce or eliminate pollen contamination of future seed crops, make sure to clean pollination chamber between each pollen release.

An alternate approach is to use a small paint brush to “paint” pollen onto the pistils. Dip the brush in the pollen container and gently brush the pollen onto the pistils. Again, the breeder must have a steady hand to ensure pollen doesn’t become airborne during the process. This technique is perfect if the cultivator only needs to make a few seeds.

After fertilization, most seeds will be fully ripe in about six weeks, although some may be viable earlier. As the seeds mature, they can split open the calyzes allowing the breeder t see the development of the seed within. Seeds are ripe when they are mostly dark brown or grey, well-mottled (tiger striped), and sitting loosely in the calyx. Green, yellow, or white seeds are almost always immature and not viable. Sprinkle them on your salad r cereal. To test the ripeness of the seed crop, you can sample harvest a few seeds and try to press them between your thumb and index finger to test the firmness. If most of the seeds do not crush with a reasonable amount of pressure, it’s time to harvest. If seeds are left on the plant too long, some may fall out of the buds and germinate on the growth medium below. This is more common with sativa dominant varieties. Indica varieties typically have more dense flowers, which hold the seeds more tightly. Breeders must remove seeds from indicas by crushing and sorting the seeds from the plant matter.

Seeds are ready to plant immediately, but the initial germination rates may be low. Germination rates can be increased by drying seeds out post harvest, leaving them in a cool, dark, well ventilated area for a few weeks, and then placing them in the refrigerator fr one or two months before sprouting.

Please keep in mind this is only a guideline intended for small scale seed production. Any method where pollen comes into contact with a pistil will result in seeds. Often breeders and seedmakers will place multiple males, or multiple copies of the same male (clones from a father donor plant) in the seed production grow room with their chosen females when creating seeds. Placing these males in a well ventilated room and allowing full release of pollen ensures the crop will be completely pollinated, and produces a vast amount f seeds per plant. Scale the process to suit the number of seeds you require.

Seed Crop Care

Typically, cannabis growers use a high phosphorus, low nitrogen diet during the flowering cycle. My personal philosophy is to give seed production plants a complete balanced diet throughout the seed gestation period, so all nutrients required for proper development of the seeds are available. Because most cannabis specific flowering fertilizers are low on nitrogen, growers may wish to combine vegetative and flowering fertilizers to ensure a complete diet for their seed mothers. Flowering nutrient formulas often lack certain nutrients, and the gestation period is not the time to be starving plants of these needs. Provide a complete diet, and let the developing seeds have all they need.

I’ve found that complete, balanced, organic based soil mixes produce the most healthy, viable seeds. Organic soils contain various bacterial populations that break down and digest soil amendments to make them usable by plants. Sterile salt-fertilizer based soils do not support these bacterial populations, and while they do support plant growth, they lack the “alive” quality of and organic soil. Many growers agree that organically grown pot has more flavor and taste than pot grown on a synthetic salt diet. it could well be that these organic bacterial populations provide some benefit to plant health, and thus produce more mature, healthy, viable seeds.

Breeding Terms

In order to have a discussion on breeding, there are some terms we must learn in order to fully understand the concepts.

Genetic material is inherited as described above, in the seed making section, from both the pollen donor and mother plant. The genetic material, or deoxyribonucleic acid (DNA) is coiled into long, X-shaped strands called chromosomes and stored in the nucleus of every cell. In cannabis, each individual inherits 10 different chromosomes from the staminate pollen parent, and 10 different chromosomes from the seed mother or pistillate parent. The resulting individual has 10 chromosomes total, 2 copies of each of the 10 chromosomes, or 2 full genomes. This means there are two copies of every gene in the plant, one from the mother, and one from the father. Each and every cell in the plant has a copy of this unique DNA compliment. The genetic code is written along the length of the chromosome strands, and each gene has a specific location along its length.

Phenotype – We consider phenotype as the observable, qualifiable representation of a given trait. Anything you can measure, categorize, or otherwise observe in an individual can be considered a phenotype. Every plant has many different phenotypes. For example, plant height might be broken down into three categories or phenotypes: short, medium, and tall stature. There is a short phenotype, a medium phenotype, and a tall phenotype.

Cannabis flowers demonstrate different color phenotypes as well. Most often we see green calyxes, but there are also plants that have purple calyxes. Sometimes there are even green calyxes with purple markings. These are all different calyx-color phenotypes. There are also calyx-size and calyx-shape phenotypes, or leaf size and shape phenotypes. Every trait has different phenotypes that can be selected fr or against.

All phenotypes are the observable result of genes acting within the cells of the pant. Sometimes a singe gene controls one trait (monogenic traits), and sometimes sets of genes operate together and contribute to make what we see as a phenotype (polygenic traits).

Genotype – The genotype of a plant is a way of describing the actual genetic condition that results in the phenotype. As the genetic constitution or makeup of an individual, genotypes are not always expressed. Some are latent and only express themselves given the proper environmental stimulus. For example, some plants have green leaves, but the leaves will turn purple under cold conditions. Other green-leaved plants will not turn purple even under cold conditions.

This happens because these plants have a different version of the gene(s) that control whether purple pigments are to be produced in the leaves. These different gene versions are called alleles.

These plants initially both had the green-leaved phenotype, but one plant developed an altered phenotype (purple leaf) in response to an environmental condition. This is due t interaction of the genetics of the particular plant with respect to this trait (genotype) and the environment. A simplistic way to think of the concept is: Phenotype = Genotype + Environment.

Remember, this isn’t 100% true. More accurately, the phenotype(s) seen in a given individual are the result of an interaction of the plant’s genotype with the environment.

Let’s look at some possible corresponding genotypes in our short, medium, tall phenotype example. Remember, the genotype is our way of describing the genetic condition responsible for the phenotype, therefore we can assign it whatever values we want, it’s really just a symbol.

There are always 2 alleles, or versions of every gene, including the gene responsible for stature. When we have 2 “s” (lower case s) or “small stature” alleles, we see the short phenotype in the plant. Conversely, when the plant has 2 “S” (capital S) or tall alleles, the phenotypic outcome is a plant of tall stature. If the plant happens to inherit a copy of the tall and short allele, the resulting phenotype is a plant of medium stature.

Often, breeders base the symbol for the genotype on the first letter of the recessive expression of a trait. What this means will become clear over the next paragraph or so.

Homozygous / Heterozygous – These are terms used in describing the genotypic condition of a plant, with regard to the similarity of the alleles for a given trait. If a plant is homozygous for a given trait, it has two copies of the same allele (homo = same). If a plant is heterozygous, it has two different alleles for a given trait (hetero = different).


Consider two true-breeding varieties; a white pistil variety and a variety showing only pink pistils. Both conditions are true-breeding and therefore homozygous; in each case sexual reproduction of each group separately leads to only pink pistil or white pistil plants respectively. An F1 hybrid, or the first generation cross of these two varieties, results in only white pistil plants; no pink pistils are seen regardless of how many F1 seeds are grown.

Upon sib mating of these F1 plants (crossing brothers t sisters, or mating F1 siblings), the resulting F2 generation produces 75% white pistil plants and 25% pink pistil plants. Notice the “disappearance” of the pink pistil plants in the F1 generation, and their subsequent “reappearance” in the F2 generation. In this case, white pistils are said to be dominant over pink pistils, and pink pistils are said to be recessive to white pistils.

Primary Components of a Breeding Program

Develop a vision or a breeding goal – Every breeding program should begin by developing a breeding goal. Why are you trying to make seed? What are you trying to accomplish by mating these sets of parents? You might be trying to make a seed population that represents the traits of an ideal, or mostly ideal plant you have previously selected. In the case of the latter, you might be trying to add new traits to your mostly ideal plant and incorporate these new traits into a new seedline. Some may just want some seeds to plant for next year’s crop. Think of your breeding goal as your final destination; the breeding process is the roadmap or route t get to that goal.

Find or Create Variability – Finding variable seedlots these days is certainly not a difficult task, because very few breeders take the time to stabilize or fix certain traits within a given breeding population prior to release. Your starting seed stock likely represents a range of variation for most traits, depending on the source of your initial starting material. The sad reality is that most of the seed industry today focuses more on creating seed for sale than soon developing improved or even uniform plant stock. As a breeder looking for germ plasm to work with, this leaves unstable populations with ample variation for future selection. If searching for variation, this could be considered a good thing. However, since true breeding stable plants are what breeders look for when choosing stock for their own breeding, this is a hindrance as well. It is much easier to breed with true breeding plants because one can see patterns emerging in a predictable manner in subsequent generations, and thus expect reliable, consistent results when hybridizing known true-breeding parents. This can only be achieved if the breeder is using true-breeding starting parent stock. Due to the lack of commercially available true-breeding stock to work with, serious breeders must stabilize their initial breeding stock before beginning the hybridizing or outcrossing phases of their breeding programs.

Grow and Evaluate – Do just as it says. The more plants you grow, the more variations you will see. I am repeatedly surprised and even amazed to see new expression of traits when growing this fabulous species. Cannabis is an extremely variable and polymorphic species, many traits have numerous possible expressions. Growing varied seed stocks of different heritage (and many of each population) ensures the breeder a wide array of phenotypes and combinations of traits for future selection.

Choosing from as many plants as possible is always preferable; having a wide and diverse starting stock assures the highest chances of finding what you might be looking for. When selecting from just a few seeds, it’s not possible to assure all plants will be vigorous or show the traits of interest even if they are seeds of known quality. Breeders must weed through large populations of potential plants, and “rogue out” the undesirable individuals. In any breeding program, off-types which d not suit the goal should be removed from the breeding populations.

Some recessive traits, especially those controlled by multiple genes (polygenic traits), have the potential for phenotypes that are only apparent in 1 in 100 or even 1 in 1000 plants. Unless growing many individuals, the breeder has a very ow likelihood of discovering these phenotypes. All other things being equal, the breeder who grows the most plants has the greatest possibility of finding the best breeding candidates. Testing the final product is a crucial part of the evaluation process, so get out that bong r those rolling papers and put all your hard work to the test!

Screen, Select, and Apply Selection Pressures

To paraphrase one f the great breeders of the 20th century, select only plants that closely match your goal, and reject all others. This is an important rule to follow if your future generations are to gradually approach your goal.

Breeders select plants for future breeding on the basis of their desirable characteristics. There is no “right” or “correct” ranking of priority for selecting one trait over another; this is purely based on what traits are most important to the breeder. For indoor cultivation, these include short, squat, bushy growth; large, densely formed buds; discernible taste or particular flavors and aromas; high THC content and quality of high (long lasting, soaring, sedative); and resistance to specific insects r diseases. It’s a good general rule to look for pants with overall vigor and good health.

Sometimes, we find a plant that is almost ideal in every respect, but has some negative trait that is undesirable. For example, the breeder may select a highly potent plant that produces exceptionally aromatic or flavorful flowers but is tall and lanky and difficult to grow indoors under artificial light.

Post-harvest selection requires either partial seeding of each plant (only seeds from the most potent plants are sown for successive generations) or keeping cone copies of each and every plant, for future seed production use once post harvest evaluations are done.

Commercialize – This is an optional part of a breeding program. Some people breed to create a variety tat suits their specific growing environment and smoking tastes, without ever intending to profit from the sale of their work. They just want reliable seeds for their own planting and future use. Some are of the opposite extreme; they make seeds exclusively to sell. These “breeders” do very little breeding. We refer to them as seed makers.

Because cannabis is a species under attack from various governments and other evil forces around the world, true breeders with goals and intentions other than financial are solely needed to protect the genetic resources cannabis has left. Years of persecution from governments and greedy seed-making practices without improvement or preservation have led to a genetic bottleneck, a narrowing of the potentially available breeding stock. Now more than ever, ethical breeding should be of utmost concern to cannabis enthusiasts. The species desperately needs breeders who are willing to improve populations in their possession, all the while preserving valuable genetic resources for future generations of breeders.

Sam the Skunkman, a great ally of cannabis, says we all stand on the shoulders of those who have come before us. We can build upon the improvements our ancestors have made to landraces and wild populations, but we can only work with what they have left us. Selections and advancements come at a cost t genetic variability. Breeders often reduce variability by narrowing the gene pool of that particular population as a consequence of fixing traits. The best breeders strive t advance and improve a given variety or population while preserving the variation present for the traits not under selection, which may prove valuable for future breeders and growers.

Types of Seed Populations

Inbred Line / Pure Line – Some refer t these as IBLs. An inbred line is a seedlot that has been bred for generations while selecting repeatedly fr specific traits, to the point where the population reliably produces the traits under selection in each successive generation of breeding. These plants are said to breed true for these characteristics. There is little or no variation for these traits, which are thus considered pure. Pure lines make the best breeding stock as the progeny of crosses using breeding stock as the progeny f crosses using known pure parental lines have a predictable outcome in subsequent generations. Inbred lines are uniform in growth patterns and traits and are stable genetically – each generation of inbred seed results in plants similar in most ways to the previous generation. Pure lines are homozygous at most alleles.


Hybrids are a product of a cross between genetically unlike parents. Hybrids retain their distinctive characters if reproduced asexually but fail to reproduce these characters completely or reliably when reproduced sexually. Hybrid cultivars are developed by using available inbred lines or creating new ones from segregating populations, and then coupling selection with inbreeding for homozygosity, evaluation of inbreds for combining ability in hybrid combinations, and subsequent multiplication of selected inbred lines for hybrid seed production.

F1 hybrid varieties

An F1 hybrid population is obtained by crossing two unrelated, true breeding varieties. F1 hybrids are unique in that they are uniform when grown from seed, but, like all hybrids, are genetically unstable. If reproduced sexually by inbreeding within the F1 population, the subsequent generation will be neither uniform nor similar to the F1 generation.

One of the major benefits of F1 seed to the grower is a condition known as hybrid vigor, or heterosis. Hybrid vigor occurs when the progeny resultant from crossing the two parental inbred lines exceed the performance of the parental lines in some character, or most often in sets of characters (F1 < or > P1 or P2).

F1 hybrids are often bigger and more robust and grow faster than either of the parent populations used in the creation of the F1 population. For example, a (Skunk#1 x Blueberry) F1 hybrid may grow faster and yield more than either the pure Skunk#1 or Blueberry parent populations. Often, heterosis is apparent as a tolerance to adverse environmental conditions.

F1 seed production has benefits to the breeder or seed maker, as well as the grower. True breeding seed can be easily reproduced by open-pollination. Most seed companies have no interest in selling easily reproduced seeds. This is as true of corn as it is of cannabis. Very few companies that do take the time and effort to breed stable parent stock release it in a pure from. Most make and release hybrids, as certain competitor companies’ sole mission is t create knockoff versions of lines released by those who have actually taken the time to develop new true-breeding lines. By releasing only hybrids of their pure lines, seed banks ensure the customer come back to buy more of the F1 seed each time they wish to do a new seed planting of the variety. They also protect the investment of their long term breeding effort by removing the possibility that a competitor will reproduce their work and sell it as their own.

Unfortunately, breeders of cannabis drug varieties have no recourse to the law when others reproduce and market their years of work. Due to the illegal nature of the plant, drug cannabis varieties are not protected by the various plant breeder’ rights legislation around the world. There is, however, at least one drug type cannabis cone registered for plant protection in Holland. The clone registered as “Medsins” is owned for use by a pharmaceutical company licensed to grow cannabis for pharmaceutical production.

Variety – A subdivision of a kind, group, or family that is distinct in some characters. Within the variety, all plants exhibit a set of defined morphological, physiological, or other chemical characteristics that differentiate the variety from all other varieties. The variety must be uniform. Variations in essential and distinctive characters are described and characterized by the breeder. The variety will remain unchanged to a reasonable degree f reliability in its essential and distinctive characteristics and its uniformity when reproduced.

Cultivar (abbreviated cv) – A term derived from “cultivated variety”, a population of cultivated plants clearly distinguished by any number of morphological, physiological, cytological, or chemical characteristics. When reproduced sexually or asexually, the population retains its distinguishing characters.

New selections derived from a cultivar or variety such that the selection shows sufficient variation from the parent cultivar to render it worthy of a name, are to be regarded as a distinct cultivar.

Strain – Strain is not a scientifically accepted botanical term, although in the cannabis industry many use the term when discussing seedlots for purchase, for lack of a more accurate term. Strain is a term incorrectly applied t selections of cultivars or varieties. In the cannabis seed industry, very few seedlots can be considered true varieties or cultivars, because they are not uniform or do not breed true. All plants within the population do not reproduce the defining characteristics, and, usually the variations in the defining characteristics are not described. Very often, commercially sold seeds are nothing more than hybrids of hybrids with names, and there are no defining characteristics of the “strain”. Perhaps “family” or “group” are more appropriate terms.

Open Pollinated Varieties – Non-hybrid populations reproduced by random pollination within the variety. Al pistillate individuals have the potential to mate with all staminate individuals as the pollen spreads randomly, ensuring preservation of the genetic diversity within the breeding population. In cannabis, open pollination is carried out by planting the breeding population together in a given plot isolated from other pollen sources and left to the will of the wind. To maintain varietal purity, hemp breeders ensure there is no non-varietal pollen source within fur miles upwind, and one mile downwind – which should demonstrate just how far cannabis pollen can travel on the wind.

Heirloom varieties / Heirloom seeds are the product of many years of selective planting and seed saving. The original seeds bore a plant or flower that had particular traits the grower liked – typically flavor, color, or psychoactive effect. The grower then saved the seeds from the desirable plant and repeated the process the next season selecting for similar type plants. The term “heirloom seeds” came about because the selection process fr some cultivars has been going on for generations, often passed along within a family and/or shared with friends.

Heirloom varieties are non-hybrid (open-pollinated). This simply means that they breed relatively true. Thus, growers can save seeds from their crops, pant them the following year, and expect to see offspring that are much like the parent generation. Any ff-types in each generation should be rogued out of the breeding population to keep it pure, as they are likely the result of pollen contamination from an external source.

Multi-line – Two or more pure-breeding lines, which are very similar, but differ in a small part of the overall phenotype (i.e. maturation, disease resistance). The varieties are grown and bred separately but are subsequently mixed together and sold in the same seed package. These packs are a benefit to growers if the grower’s given environment is inconsistent from year to year, or for growers who are experimenting with growing in a new location. For example, a multi-line may include a slightly earlier maturing variety with a slightly more mold-resistant variety; most other traits are equivalent in each population. The variations in performance of each variety with regards to mold or earliness of maturity ensure that there will be some harvest even in a year where only the early varieties finish (as a result of early rains), or even if mold is more prevalent during the particular grow season. If a grower is new to the area, multi-lines may be useful for the first few years of planting. It is always a shame to plant a single variety, only to find it is not suitable for the particular climate, thus wasting the year of production. The grower may not reap the highest yield as may be possible from a single hybrid variety particularly suited to the climate, but the degree of variation present in multi-lines helps to ensure that least some plants are harvested.

Synthetic variety – an interbreeding population derived from inter-mating a group of specific genotypes, each of which were selected for good combining ability in all possible hybrid combinations. Subsequent maintenance of the variety is achieved by open pollination and usually involves rounds of recurrent selection over a series of generations.

intersexuality is a trait that can be expressed due to a multitude of causes, both genetic and environmental. There are intersex plants which are strictly genetic; these plants have inherits a gene that triggers the intersex condition, even given a perfect growing environment. They produce both pistillate and staminate flowers on the same individual under typical environmental conditions. Strict negative selection against these plants is required by breeders and growers in order to eliminate the intersex trait from the breeding population. Cultivators and breeders alike have wisely selected against plants that show the slightest degree of intersexuality. They know even a single male flower on an otherwise female plant can result in the majority of the crop being pollinated, and thus seeded.

Indoors, where growers attempt to mimic Mother Nature, plants often undergo stresses which are not present under natural conditions. When plants are stressed by being grown in an inhospitable environment, the typical expression of characteristics can be altered. Intersexuality, for example, can also be induced in cannabis by a grower’s influence as a result of an inconsistent growth environment.

Environmentally stressed female plants have been known to show occasional male flower. Interrupted dark cycles and other types of stressors can result in the development of staminate flowers on otherwise pistillate individuals. Environmental conditions which may provoke sexual reversal include an inconsistent photoperiod, nutrient toxicities and deficiencies, pH issues, or drastically fluctuating temperatures during the flowering cycle. Females severely stressed, for any reason, are more prone t develop a few male flowers. These stresses cause changes in the levels of a plant hormone called ethylene.Ethylene is one of only a few known plant hormones, and plays many roles in plant development across a range of species. In cannabis, one of ethylene’s major roles is its involvement in the determination of sex. It regulates which flowers should be produced – stamen or pistil. We know this because applying high enough concentrations of ethylene to staminate individuals in the flowers cycle results in the formation of pistils. Conversely, applying ethylene-inhibiting agent to pistillate individuals as they enter flowering results in the formation of stamens in place of pistils. This practice can be of use to breeders in the creation of “feminized” seeds, or all-female (gynoecious) seedlots.

All female seeds are produced by obtaining pollen from one female individual, and subsequently fertilizing another female plant.

When we previously discussed chromosomes, we said there were 20 chromosomes in each cell of the plant. The 10th pair of chromosomes, the smallest pair, are the sex chromosomes. Female cannabis plants have two copies of the X chromosome, therefore their genotype is XX. Male plants have only 1 copy of the X chromosome, and a Y chromosome instead of a second X chromosome. The genotype of male plants in terms of the sex chromosomes is XY.

When pollen is created within the plant, one of each of the chromosome pairs is packaged into the cells that develop into pollen. Each pollen grain or ovule contains 10 chromosomes, 1 copy of each pair. When the pollen deposits the genetic material into the ovule, the 10 chromosomes, from the pollen and the ovule unite t make a total of 20 chromosomes, a full genetic compliment.

Some growers intentionally use the pollen from intersex plants to fertilize females. They have found that the seeds and subsequent offspring produced from this union will be predominately female. The major problem with this technique is that these plants will have intersex tendencies. by selecting parent plants that have intersex tendencies, we ensure that some of the progeny will also have intersex tendencies. Using pollen from an intersex or hermaphrodite plant is an intentional selection for intersexuality – like begets like.

So how d we get true females (that do not show any degree of intersexuality under normal conditions) to produce pollen? Can we get pollen from female plants that do not show a degree of intersexuality?

There are hormone treatments, which, when applied t cannabis, result in the formation of staminate flowers on otherwise pistillate plants. To select against the intersex condition, we take our chosen female breeding candidates and grow them under stressful conditions that may lead to the formation of male flowers – irregular light cycle, high heat, etc. Only plants that resist intersexuality under these conditions should be considered as potential breeding parents for the creation of all-female seed lines. We call these intersex-resistant plants “true females”. Intentional selection against intersex plants is the only way to ensure intersex-free offspring.

Clone copies of these pistillate intersex-resistant plants are then sprayed with our hormone treatment and placed into the flowering cycle and allowed to develop stamens. It typically takes three to five weeks for the plants to enter dehiscence and shed pollen. True female candidates that also resist intersexuality under typical stresses, are pollinated by pollen obtained by our hormone-treated, gender-reversed, stamen-bearing female plants. The result is a true gynoecious population, consisting entirely of female plants.

An American company, Hybritech, was the first to introduce an effective ready t use hormone treatment- eliteXelite. This product is no longer available for public purchase. Another plant research firm, PG-Solutions, has since developed and released a ready t use hormone therapy spray, Stamen-It!. Stamen-It! is extremely effective in causing gender reversal of pistillate individuals. Some hormone sprays are able to induce staminate flower formation, but fail to produce viable pollen in any significant quantities. PG-Solutions has developed a formulation that causes significant pollen production, even in the most reversal-resistant genotypes.

Breeding Schemes for Cross-Pollinated Crops

There are many types f breeding programs, some more complex than others. Which breeding method to employ depends entirely on the breeder’s goal. Ideally, potential breeders understand the benefits and drawbacks of each strategy, so a suitable strategy can be chosen to achieve the desired goal. The breeder’s personal preference always comes int play when choosing a breeding program. Previous successes may influence a breeder t use one specific breeding strategy over another. Some breeders rely heavily on science and statistics when analyzing the performance of their hybrids or progeny. Others consider breeding more of an art, and select based on feeling. Over the course of a breeding program, a breeder will often use more than one method to achieve various aspects of the goal.

When breeding cross-pollinators, we discuss hybrid performance in terms of combining ability – the ability of an inbred line to give characteristic performance in hybrid combinations with other lines. The progenies are tested for performance as populations and related back to the parental generation. Some often-used measures of performance are general combining ability (CGA) and specific combining ability (SCA). General combining ability is the average or overall performance of a given line in hybrid combinations open-pollinated with other lines.

Specific combining ability is the performance of a specific line, as compared to other lines, when crossed with the same specific pollen source.


Inbreeding is nothing more than crossing a group, family, or variety of plants within themselves with no additions of genetic material from an outside or unrelated population. The most severe form of inbreeding is the self-cross, in which only one individual’s genetic material forms the basis of subsequent generations. 1:1 hybrid populations are only slightly less narrow, derived from the genetic material of 2 individuals. Such tight or narrow breeding populations lead to a condition called “inbreeding depression” upon repeated self-breeding of inbreeding.

Inbreeding depression is a reduction in vigor (or any other character) due to prolonged inbreeding. This can manifest as a reduction in potency or a decrease in yield or rate of growth. Progress of depression is dependent, in part, on the breeding system of the crop. Earlier, when we discussed dioecy, we said cannabis is an outcrossing or cross-pollinating species. Cross-pollinated crops usually exhibit a higher degree of inbreeding depression when “selfed”, or inbred, than do selfing crops. For example, tomato (an inbreeding or selfing species) can be selfed for 20 generations with no apparent loss in vigor or yield , whereas some experiments have shown that the yield of corn per acre is decreased quite dramatically when inbred for 20 generations.

In cross-pollinated crops, deleterious genes remain hidden within populations, and the negative attributes of these recessive traits can be revealed or unmasked via continual inbreeding. Inbreeding depression can be apparent in S1 populations after a single generation of self-fertilization. When breeding cannabis using small populations, as is often the case with continual 1:1 mating schemes, inbreeding depression typically becomes apparent within three to six generations. To deal with this problem, breeders often maintain separate parallel breeding lines, each of which are selected for similar of identical sets of traits. After generations of inbreeding, when each of the inbred lines, or selfed populations, begin t show inbreeding depression, they are hybridized or outcrossed to each other to restore vigor and eliminate inbreeding depression while preserving the genetic stability of the traits under selection.

The vast majority of texts written to date on the subject of breeding cannabis have espoused 1:1 mating strategies, much t the detriment and health of cannabis germplasm. Sadly, this is the preferred breeding scheme used today by the majority of commercial seed banks. These breeders don’t realize that cannabis is naturally an out-crossing or cross-pollinating species and existed in wild breeding populations of hundreds if not thousands of individuals. Within these many individuals lies a wide range of versions of different genes. When we select only one or two plants from this vast array as our breeding population, we drastically reduce the genetic variability found in the original population (a genetic bottleneck). This variability is lost from the populations, and unavailable to future generations.


Outbreeding is the process of crossing or hybridizing plants or groups of plants with other plants to which there is no, or only a distant, relation. Any time a breeder is hybridizing using plants that reside outside of the family, group, or variety, hybrid seed is produced. For example, an F1 hybrid seed is the first generation offspring resulting from a cross of two distinct true-breeding plants or populations. Each of the parent populations were hybridized (outcrossed to each other) to produce the new generation, which is now comprised of genetics from both parental populations. Outcrossing results in the introduction of new and different genetic material to each of the respective pools.

Filial Breeding

A type of breeding system where siblings of the same progeny lot and generation are intermated to produce new generations. The first hybrid generation of two distinct true-breeding lines is denoted the F1 generation (F, filial). If two F1 siblings are bred, or the F1 population is allowed to be pen pollinated, the resulting generation is labeled F2.

Mating siblings chosen from the F2, results in the F3 population. F4, F5, F6 generations, etc., are obtained in the same manner, by crossing plants of the same generation and progeny lot. Note that as long as any number of siblings of a generation (F[n]) are mated, the resulting generations is denoted (F[n+1]).

Filial inbreeding with selection for specific traits is the most common method for establishing a pure or a true-breeding population, when breeding cross-pollinated species such as cannabis.

Backcross Breeding

A type of breeding that involves repeated crossing of progeny with one of the original parental genotypes; cannabis breeders most often cross progeny to the mother plant. This parent is known as the recurrent parent. The nonrecurrent parent is called the donor parent. More widely, any time a generation is crossed to a previous generation, it is a form of backcross breeding. Backcross breeding has become one of the staple methods clandestine cannabis breeders use, mainly because it is a simple, rapid method when using greenhouses or grow rooms, and requires only small populations. The principal goal of backcross breeding is to create a population of individuals derived mainly from the genetics of one single parent (the recurrent parent).

The donor parent is chosen based on the trait of interest that the recurrent parent lacks; the idea is to introgress this trait into the backcross population, such that the new population is comprised mainly of genetics from the recurrent parent, but also contains the genes responsible for the trait of interest from the donor parent.

The backcross method is a suitable scheme for adding new desirable traits to a mostly ideal, relatively true-breeding genotype. When embarking on a backcross breeding plan, the recurrent parent should be a highly acceptable or nearly ideal genotype (for example, an existing commercial cultivar or inbred line). The ideal traits considered for introgression into a new seed line should be simply inherited and easily scored for phenotype. The best donor parent must possess the desired trait, but should not be seriously deficient in other traits. Backcross line production is repeatable, if the same parents are used.

Backcross breeding is best used when adding simply inherited dominant traits that can easily be identified in the progeny of each generation. Recessive traits are more difficult to select for in backcross breeding, since their expression is masked by dominance in each backcross to the recurrent parent. An additional round of open pollination or sib-mating is needed after each backcross generation, to expose homozygous-recessive plants. Individuals showing the recessive condition are selected from F2 segregating generations and backcrossed to the recurrent parent.


Selfing is the process of creating seed by fertilizing a plant with pollen obtained fr itself. The result of the self-cross is a population of plants that derive from a single individual. The first generation population is derived from selfing an individual is called the S1 population. If an individual is chosen from the S1, and gain selfed, the resulting population is denoted the S2 generation. Subsequent generations derived in the same manner are denoted S3, S4, etc.

Traits for which the plant is homozygous remain homozygous upon selfing, whereas heterozygous loci segregate, and may demonstrate novel expressions of these characters.

We know homozygous loci remain homozygous in future generations upon selfing, but what about the heterozygous loci? Each selfed generation leads to an increase in homozygosity by 50% for each heterozygous locus, and each subsequent generation, derived from selfing an S1 individual, is 50% more homozygous than the parent from which it was derived. Repeated selfing, or single-seed descent, is the fastest way to achieve homozygosity within a group or family. Again, the more plants grown from a selfed population, the better probability a breeder has of finding selfed progeny that show all of the desired traits.

Single-seed descent

A plant is self-fertilized and the resulting seed collected. One of these seeds is selected and grown, again self-fertilized, and seed produced. All progeny and future generations have descended from a single ancestor, as long as n pollen from an external family is introduced. Each generation is the result of selfing one individual from the previous generation.

After six generations of selfing without selection, 98.44% of the genes of an individual are homozygous – this refers to genes, not the number of plants that are homozygous.

Recurrent Selection

Any breeding program designed to concentrate favorable genes scattered among a number of individuals by repeating cycles of selection for favorable traits.
Step 1 – Identify superior genotypes for the trait under selection.
Step 2 – Intermate the superior genotypes and select improved progeny.
Step 3 – Repeat steps 1 & 2 over a series of generations.

Pedigree Selection

A system of breeding in which individual plants are selected in the segregating generations from a cross on the basis of their desirability, judged individually, and on the basis of a pedigree record.


Cannabis plants are, by nature, diploids with twenty chromosomes. At meiosis, each parent’s gamete contributes ten chromosomes to the zygote they have formed. Cannabis cells may be haploid as in gametes, or diploid.

Some researchers have wondered whether triploid, or tetraploid cannabis (cells with either 3 or 4 chromosome sets respectively) are agronomically important. In some species, polyploid plants grow bigger, yield more, or outperform typical diploid members of the same species. Some early reports touted polyploid cannabis as being more potent. This research was flimsy and unscientific at best, and ever since this report, many cannabis growers have attempted inducing polyploidy in many varieties, none leading to agronomic success.

Diploid plants are considered normal and have one set of chromosomes, which occur in pairs within each plant cell. Poyploid plants have more than one set of chromosomes per cell. Polyploid plant chromosome occur in groups of 3-4 instead of in pairs. Tetraploid plants group occur with four chromosomes in each cell.

At one time, breeders believed that polyploid and tetraploid plants would produce a superior resin-packed plant.

The polyploid characteristic can be induced with an application of colchicine. Just remember, colchicine is a poison, and polyploid plants do not contain more THC-potent resin.

Mutagenesis-Inducing Variation

If variation does not exist for the trait or traits of interest, or cannot be found in other populations, it is theoretically possible to induce variation by exposing seeds or other tissues to radiation, alkylating agents, or other mutagens such as colchicine or EMS (ethylmethylsulfonate). These treatments cause changes at the DNA level that have the remote potential to result in desirable, novel phenotypes.

There is much rumor and speculation about this technique amonst breeders and growers. It’s a common myth that treating seeds with colchicine and growing the plants results in more potent cannabis plants. Let’s put this myth to rest; it is completely untrue. While the possibility does exist on a theoretical level, no valid experiments have ever shown this to be true. Potential breeders would be better off using their time an space for selecting better plants than trying this technique as a method for improving plant stock. That being said, let’s take a look at the theory behind the concept.

Imagine you have a population of plant which, when grown from seed and inbred within the population, consistently produces high-THC plants. It is theoretically possible to treat many of these seeds with a mutagen, grow and inbreed the seeds, and find plants in subsequent generations that produce no THC. These mutagens can destroy genes along a chromosome, and when copies of this chromosome are inherited by future generations, a new or “novel” phenotype can appear. In our example, the no THC condition is the novel phenotype.

These mutations, however, occur at random and are extremely unreliable. The probability of finding plants which have the desired mutation in the gene of interest is very low. A breeder may treat many thousands of seeds, grow 100,000 plants, and still not see the desired altered phenotypes. This technique is costly in both time and space. It is often used in breeding of “legal plants” when growing our thousands of individuals and searching for these novel phenotypes is not problematic. Performing such population screens in cannabis is not practical, especially for clandestine breeders. The potentially hazardous nature of these mutagenic agents is another very good reason to choose other breeding options. Inducing variability is likely not the best option, at least for the hobby breeder.

Marijuana Horticulture

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