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

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.

Hermaphrodite plant with both female and male flowers together.
    Environmentally stressed female plants have been known to show the 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 to 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 flowering cycle results in the formation of pistils. Conversely, applying ethylene-inhibiting agents 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.

Applying a hormonal spray is easy.
    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 chromsomes 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 to make a total of 20 chromosomes, a full genetic compliment.
    Let’s examine a Punnet square from a typical male: female cross -
    Male genotype = XY
    Female genotype = XX

    From above we can see that half of the plants are XY (male) and half of the plants are XX (female).
    Let’s now look at a Punnet square from a female:female cross -

    This Punnet square shows us that female: female breeding schemes produce only female (XX) offspring.
    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.
    Some seed companies market “feminized seeds,” which are produced by collecting pollen from carefully selected, latent, stress-induced hermaphrodites, and use it to pollinate female plants. This process is time consuming and arduous, but yields mostly female plants when grown without stress. However, under the stresses that resulted in the intersexuality for the pollen parent, the progeny will often show some degree of intersexuality as well. Again, like begets like.
    So how do 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 to 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