Education, General Horticulture, Lighting, Selective Breeding

Cannabis Genetics 101

By Nico Escondido

Cannabis Propagation

There are two primary methods by which Cannabis plants are propagated. The first is via sexual reproduction where plants are propagated by seeds and designated as a specific plant line or strain. Seed germination is the most basic method for starting a particular strain. Seeds, however, are not always identical reproductions of a singular genotype. As in any sexual reproduction, one male and one female plant combine to form a new hybrid seed. Unless, both the male and female are from the exact same lineage, the offspring will have varying traits from both parents. Finding both male and female parents of the same lineage can be difficult and even if accomplished it still does not guarantee that the offspring will express identical phenotypes.

A second method for plant propagation is an asexual technique where plants are propagated as clones. Clonal propagation is fundamentally different than seed propagation in that clones originate from vegetative propagation from a single parent plant (in the case of marijuana, it is almost always a female mother plant, unless a breeder needs loads of pollen from male plants). Clonal propagation is fast becoming the most popular choice for propagation amongst growers because growers know exactly what they are getting from the mother plant. Clone are especially effective for larger grows and commercial operations as they generally propagate faster than growing from seed and take the guess work out of weeding out unwanted male plants from the gardens.

Seeds are becoming harder and harder to find (for free) as the quality of marijuana increases. This is because the most potent marijuana is seedless, or sinsemilla (meaning “without seed”). Still, seeds can be procured in a variety of ways, most of which will cost a grower a little bit of money.

Buying seeds directly from breeders is often the best bet in order to ensure true-breeding, quality seeds. However, obtaining seeds from reputable seed banks (retailers) or larger distribution companies have also become viable and safe methods for buying Cannabis strains. Of course, the best (and perhaps luckiest) way to secure seeds of your favorite strains is to pull them right out of the bag of ganja you just bought from your marijuana supplier. This requires a bit of luck, though, as most quality strains are grown in isolation, without the presence of male plants that can pollinate buds and thus create seeds. Still, even the best ganja can sometimes naturally hermaphrodite and self-pollinate itself, making a few rare seeds. Hermaphroditic plants can often become a grower’s best friend.

A major problem in breeding is how to produce seeds without diluting the desired genetic line. Because seeds require pollen in order to form, breeders need to find both a male and female of the same strain that both possess the particular phenotypes that the breeder wants. Sometimes finding a male plant of a particular line can be daunting as more and more growers turn to clonal propagation, thereby shrinking the male plant population significantly. Some breeders force their plants to unnaturally hermaphrodite via the use of chemicals to solve this dilemma. This is also how breeders have come to create the new and trendy feminized seeds. However, these seeds often have stability problems and have high rates of hermaphrodation themselves.

Selection of Phenotypes

The selection process in creating new strains is perhaps one of the most important aspects of breeding. Selection is the process of finding both a male and female plant from specific genotypes with which seeds will be produced. Selecting different genotypes for use in sexual reproduction will result in the creation of a new hybrid strain. Selection of a male and female from the same genotype (line) will result in a new generation of that same genotype that may or may not express the same phenotypes of the parents.

Breeders are most often interested in crossing two different genotypes for the purpose of inventing a new strain that hopefully has new and desirable characteristics such as a different flavor or aroma or different degrees of potency. Sometimes breeders choose to use the same genotype for both the mother and father in order to strengthen characteristics that are already popular but not quite stable (meaning they don’t always reappear in the new offspring).

In order to have a successful breeding program, breeders require lots of space so that they can make selections from hundreds, or even thousands, of plants. Selection is done by visual inspection of plants in their mature state. Breeders look for basic characteristics in a population that they found favorable in the parents. These characteristics can be plant height, color, resistance to mold or insects or any one of hundreds of other traits. The bigger the selection the better the chances of finding the exact right parents.

Once parents of the same genotype are chosen, they are crossed either with each other in the hopes of uncovering hidden phenotypes of that same line or with completely different genotypes from a different or previous selection to create a new hybrid line. When crossed with the same genotype, an inbred line (IBL) is created. This can be good as it creates a homogenous garden for a grower, but it can also lead to reduced size and productivity – a condition known as inbreeding depression – if it is continued over multiple generations. In the latter example, where differing genotypes are crossed, the resulting genetic line will possess what is known as hybrid vigor, whereby the offspring show better size, strength, potency and yield than the parents, not to mention new sets of exciting phenotypes.

When two parents from differing genotypes are crossed, the result is what is called an F1 hybrid. An F1 hybrid is the first generation of a new strain. F1’s usually exemplify excellent growth and vigor, but are sometimes unstable. As such, breeders will produce hundreds of F1 seeds to grow out and then select for the desirable traits. Once the selection is complete, a breeder may choose to re-cross this new hybrid with one of the parents in order to stabilize, or strengthen, a particular characteristic. This is known as backcrossing. In order to backcross to original parents, breeders must have an in-depth knowledge of both the strains they are working with as well as how genes work.

How Genes Work

Genes are the basic physical units of heredity. They provide the coded instructions within DNA that lead to the expression of hereditary characteristics. Gene pairing creates a pattern of genetics that is unique to each plant. These gene pairs are can be likened to a zipper, where each side is comprised of a specific gene – one that is inherited from the mother and the other that comes from the father.

Gene pairs are denoted by a pair of letters such as CC, Cc, Nn, nn etc. Capital letters will refer to dominant genes while lowercase letters will refer to recessive genes. Different letters refer to different traits of the plant and any letter can be assigned to any gene pair when creating a breeding program.

An essential part to understanding how genes are expressed is to understand the relationship of phenotypes and alleles. As we know, a phenotype is a summary of all recognizable characteristics of plant (including smell, color, height, etc.) brought about by environmental conditions. An allele is the specific, alternative form of any one gene or characteristic. This differentiation is important to remember because it can help breeders isolate specific traits of a phenotype that are desirable for the next generation of offspring in a breeding program.

Essentially, breeders try to figure out the frequency with which alleles of a particular trait are expressed. A principal of genetics known as the Harvey-Weinberg Model illustrations a basic understanding of this equation by stating that dominant alleles will not necessarily always have the highest frequency (or appearance) within a population. Nor will the recessive allele always have the lowest frequency. This means that when creating hybrids through the crossing of two different strains, the dominant trait will not spread to he entire set of offspring nor will the recessive traits die out completely.

Knowing this, breeders will map out their breeding program by assigning letter values to every possible allele of a given phenotype. This is why having a lot of space for a large-scale selection is so integral to the breeding process. In order for breeders to ensure they have uncovered every possible allele they first need to grow out large quantities of each parent and then an even larger number of their offspring. Once this is done and a population of a given gene pool is grown out, breeders can calculate the frequency of occurrence for a given trait by dividing the number of a specific type of allele by the total number of alleles in the gene pool.

Once a breeder selects those traits that he or she wants to breed into a new strain, they can determine by the frequency of those alleles whether or not backcrossing should be done in order to attain, or bring out, those desired alleles. If the frequency of those traits occurs in only a small percentage of plants, the breeder may decide to try backcrossing to a parent that possessed that allele as a dominant trait, thus redefining that allele and possibly making a more dominant trait with a higher frequency of occurrence.

How Seeds Are Made

A seed is matured ovule that contains a living embryo. Seed are usually the result of sexual reproduction between two existing lines of Cannabis, whereby a male plant pollinates a female plant. Sometimes, however, seeds are formed from a single parent plant that has become a hermaphrodite, displaying both male and female flowers and self-pollinates to create seed (this most commonly occurs in female plants).

Seeds have three main components; the embryo, storage tissue/ food supply and a protective covering. Female Cannabis flowers, which are the buds that we smoke, contain ovaries that hold eggs awaiting fertilization. Male Cannabis flowers look much like tiny bunches of bananas, but are really sacs full of pollen. These pollen sacs are called calyx. In nature, both male and female plants grow wild and natural pollination occurs during storms, with high winds and via animals or insects that transport pollen. Male plants tend to grow taller than their female counterparts, which helps in this natural process. Pollination usually occurs from the middle of the grow season onward, depending on region and climate.

Breeders, however, take a different approach, especially when growing indoors. Because most breeders have implemented very specific breeding programs whereby they are searching for, replicating or trying to draw out certain known alleles, they must be very careful with how they pollinate seed crops. Females in breeding programs are grown in strict isolation and male plants are kept in separate housing until the female flowers are ready for fertilization. This is selective breeding. Cross-pollination, or pollination from multiple male plants of varying lines, is a breeder’s worst nightmare.

Breeders most often want fertilization of their female flowers to occur somewhere between the third and fifth week of flowering. This really depends on the strain of female being grown and the average finishing time of that strain. Most breeders will try to pollinate no less than four weeks prior to harvest otherwise the result may be nonviable seeds. Sometimes it can take as long as six weeks for some females to produce viable seeds.

Males can drop pollen starting from 12 hours after their initial calyx formation and can continue for up to four weeks after. It’s important to know that under a 12/12 photoperiod, males will produce their highest amounts of pollen. Males can drop pollen at anytime, even under 24/0 or 18/6 vegetative photoperiods. This is why many breeders try to manually collect pollen from isolated males in places far away from flowering ladies.

There are two methods for pollinating female flowers. The first and most obvious choice is to simply move a male plant into an all-female flowering growroom (or tent – which happens to work very well for breeding projects). This technique will allow for an artificially natural pollination to take place whereby fans and room air flow will act as wind and pollinate all the female plants in the room. Still, this method may not result in even coverage.

The second technique, eluded to above, is to methodically apply pollen to female flowers manually. To do this, pollen from makes must first be collected and stored. This is fairly easy to do and involves simply tapping a calyx and catching the falling pollen in a container that is non-transparent and can be sealed airtight. Make sure to label your pollen containers carefully! To manually fertilize females, breeders will use small brushes or cotton swabs, dipping them in pollen containers and then gently brushing the pollen directly onto selected buds. This process is very popular because it does not necessitate pollinating the whole plant and some choice buds can still be kept sinsemilla, or without seed.

After pollinating the female plants it is critical to maintain the same 12/12 light cycle that the flowering females have been in. Disrupting this photoperiod can have adverse affects on seed production. Not to mention, anytime a grower changes the photoperiod abruptly or mid-cycle, the stress put on the plant can trigger a hermaphrodite effect, causing the creation of both selfed (created when one hermaphroditic parent fertilizes itself) and standard seeds. This will render the breeding project virtually useless, as the two types of seed will be indistinguishable.

One last important point worth mentioning is that in some instances pollination mistakes can actually be reversed. Pollen is easily removed by washing down female plants with fresh water. Water will render the pollen nonviable. While this may disrupt trichome development, it will also prevent the production of seeds and can save unnecessary headaches.