Synthetic Variety

Marijuana Horticulture

by Jorge Cervantes

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.