Breeding Cannabis
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 to 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. 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 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 characteristics, 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. 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) is easy. Male plants are distinguished by the appearance of “pollen sacks”, or anthers, that grow from branch unions. Anthers look similar to 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. Males often bolt, or stretch, when they enter their floral development stage. Females can be distinguished by the development of two whitish hairs, stigmas, which develop as part of the pistil. The pistil is the female flower that appears in branch unions or “nodes”.
Cannabis is one of the only annual plants that produces each of the male an female sexual organs on different individuals. This is a condition know as dioecy. Dioecious plant groups contain individual plants that are either male (staminate; stamen bearing) or female (pistillate; pistil bearing). 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 drug cannabis cultivators but are more correctly referred to 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 later in this chapter.
The Creation of the Seed
Cannabis is an anemophilous species; this is a fancy way of saying that it is wind-pollinated. Under natural male plants undergo dehiscence (shedding of pollen) and disperse vast quantities of pollen into the wind. The pollen travels on air currents and lands on the stigma or style of a nearby pistillate individual. This is the pollination event. Because pollen from many species floats in the air, and there is a significant chance that pollen from other species will land on a fertile stigma of a waiting female plant, cannabis has evolved recognition systems that insure 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 are 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 burrows 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. When fully mature in four to five weeks, can be planted and will blossom into a new generation of life.
Breeding Cannabis
Cannabis seeds