# Genetics and Breeding of Cannabis Advanced Info



## ENGLAND123 (Aug 12, 2010)

*Genetics and Breeding of Cannabis​*
Genetics

Although it is possible to breed Cannabis with limited success without any knowledge of the laws of inheritance, the full potential of diligent breeding, and the line of action most likely to lead to success, is realized by breeders who have mastered a working knowledge of genetics. As we know already, all information transmitted from generation to generation must be contained in the pollen of the staminate parent and the ovule of the pistillate parent. Fertilization unites these two sets of genetic information, a seed forms, and a new generation is begun. Both pollen and ovules are known as gametes, and the transmitted units determining the expression of a character are known as genes. Individual plants have two identical sets of genes (2n) in every cell except the gametes, which through reduction division have only one set of genes (in). Upon fertilization one set from each parent combines to form a seed (2n). In Cannabis, the haploid (in) number of chromosomes is 10 and the diploid (2n) number of chromosomes is 20. Each chromosome contains hundreds of genes, influencing every phase of the growth and development of the plant. If cross-pollination of two plants with a shared genetic trait (or self-pollination of a hermaphrodite) results in off spring that all exhibit the same trait, and if all subsequent (inbred) generations also exhibit it, then we say that the strain (i.e., the line of offspring derived from common ancestors) is true-breeding, or breeds true, for that trait. A strain may breed true for one or more traits while varying in other characteristics. For example, the traits of sweet aroma and early maturation may breed true, while off spring vary in size and shape. For a strain to breed true for some trait, both of the gametes forming the offspring must have an identical complement of the genes that influence the expression of that trait. For example, in a strain that breeds true for webbed leaves, any gamete from any parent in that population will contain the gene for webbed leaves, which we will signify with the letter w. 

Since each gamete carries one-half (in) of the genetic complement of the offspring, it follows that upon fertilization both "leaf shape" genes of the (2n) offspring will be w. That is, the offspring, like both parents, are ww. In turn, the offspring also breed true for webbed leaves because they have only w genes to pass on in their gametes. 
On the other hand, when a cross produces offspring that do not breed true (i.e., the offspring do not all resemble their parents) we say the parents have genes that segregate or are hybrid. Just as a strain can breed true for one or more traits, it can also segregate for one or more traits; this is often seen. For example, consider a cross where some of the offspring have webbed leaves and some have normal compound-pinnate leaves. (To continue our system of notation we will refer to the gametes of plants with compound-pinnate leaves as W for that trait. Since these two genes both influence leaf shape, we assume that they are related genes, hence the lower-case w and upper-case W notation instead of w for webbed and possibly P for pinnate.) Since the gametes of a true-breeding strain must each have the same genes for the given trait, it seems logical that gametes which produce two types of offspring must have genetically different parents. Observation of many populations in which offspring differed in appearance from their parents led Mendel to his theory of genetics. If like only sometimes produces like, then what are the rules which govern the outcome of these crosses? Can we use these rules to predict the outcome of future crosses? Assume that we separate two true-breeding populations of Cannabis, one with webbed and one with compound-pinnate leaf shapes. We know that all the gametes produced by the webbed-leaf parents will contain genes for leaf-shape w and all gametes produced by the compound-pinnate individuals will have W genes for leaf shape. (The offspring may differ in other characteristics, of course.) If we make a cross with one parent from each of the true-breeding strains, we will find that 100% of the off spring are of the compound-pinnate leaf phenotype. (The expression of a trait in a plant or strain is known as the phenotype.) What happened to the genes for webbed leaves contained in the webbed leaf parent? Since we know that there were just as many w genes as W genes combined in the offspring, the W gene must mask the expression of the w gene. We term the W gene the dominant gene and say that the trait of compound-pinnate leaves is dominant over the recessive trait of webbed leaves. 

This seems logical since the normal phenotype in Cannabis has compound-pinnate leaves. It must be remembered, however, that many useful traits that breed true are recessive. The true-breeding dominant or recessive condition, WW or ww, is termed the homozygous condition; the segregating hybrid condition wW or Ww is called heterozygous. When we cross two of the F1 (first filial generation) offspring resulting from the initial cross of the ~1 (parental generation) we observe two types of offspring. The F2 generation shows a ratio of approximately 3:1, three compound pinnate type-to-one webbed type. It should be remembered that phenotype ratios are theoretical. The real results may vary from the expected ratios, especially in small samples. In this case, compound-pinnate leaf is dominant over webbed leaf, so whenever the genes w and W are combined, the dominant trait W will be expressed in the phenotype. In the F2 generation only 25% of the offspring are homozygous for W so only 25% are fixed for W. The w trait is only expressed in the F2 generation and only when two w genes are combined to form a double-recessive, fixing the recessive trait in 25% of the offspring. If compound-pinnate showed incomplete dominance over webbed, the genotypes in this example would remain the same, but the phenotypes in the F1 generation would all be intermediate types resembling both parents and the F2 phenotype ratio would be 1 compound-pinnate :2 intermediate :1 webbed. The explanation for the predictable ratios of offspring is simple and brings us to Mendel's first law, the first of the basic rules of heredity:

I. Each of the genes in a related pair segregate from each other during gamete formation.

A common technique used to deduce the genotype of the parents is the back-cross. This is done by crossing one of the F1 progeny back to one of the true-breeding P1 parents. If the resulting ratio of phenotypes is 1:1 (one heterozygous to one homozygous) it proves that the parents were indeed homozygous dominant WW and homozygous-recessive ww. The 1:1 ratio observed when back-crossing F1 to P1 and the 1:2:1 ratio observed in F1 to F1 crosses are the two basic Mendelian ratios for the inheritance of one character controlled by one pair of genes. The astute breeder uses these ratios to determine the genotype of the parental plants and the relevance of genotype to further breeding. This simple example may be extended to include the inheritance of two or more unrelated pairs of genes at a time. For instance we might consider the simultaneous inheritance of the gene pairs T (tall)/t (short) and M (early maturation)/m (late maturation). This is termed a polyhybrid instead of monohybrid cross. Mendel's second law allows us to predict the outcome of polyhybrid crosses also:

II. Unrelated pairs of genes are inherited independently of each other. 

If complete dominance is assumed for both pairs of genes, then the 16 possible F2 genotype combinations will form 4 F2 phenotypes in a 9:3:3:1 ratio, the most frequent of which is the double-dominant tall/early condition. In complete dominance for both gene pairs would result in 9 F2 phenotypes in a 1:2:1:2:4:2:1:2:1 ratio, directly reflecting the genotype ratio. A mixed dominance condition would result in 6 F2 phenotypes in a 6:3:3:2:1:1 ratio. Thus, we see that a cross involving two independently assorting pairs of genes results in a 9:3:3:1 Mendelian phenotype ratio only if dominance is complete. This ratio may differ, depending on the dominance conditions present in the original gene pairs. Also, two new phenotypes, tall/late and short/early, have been created in the F2 generation; these phenotypes differ from both parents and grand parents. This phenomenon is termed recombination and explains the frequent observation that like begets like, but not exactly like.

A polyhybrid back-cross with two unrelated gene pairs exhibits a 1:1 ratio of phenotypes as in the mono-hybrid back-cross. It should be noted that despite dominance influence, an F1 back-cross with the P1 homozygous-recessive yields the homozygous-recessive phenotype short/late 25% of the time, and by the same logic, a back cross with the homozygous-dominant parent will yield the homozygous dominant phenotype tall/early 25% of the time. Again, the back-cross proves invaluable in determining the F1 and P1 genotypes. Since all four phenotypes of the back-cross progeny contain at least one each of both recessive genes or one each of both dominant genes, the back-cross phenotype is a direct representation of the four possible gametes produced by the F1 hybrid. So far we have discussed inheritance of traits con trolled by discrete pairs of unrelated genes. Gene inter action is the control of a trait by two or more gene pairs. In this case genotype ratios will remain the same but phenotype ratios may be altered. Consider a hypothetical example where 2 dominant gene pairs Pp and Cc control late-season anthocyanin pigmentation (purple color) in Cannabis. If P is present alone, only the leaves of the plant (under the proper environmental stimulus) will exhibit accumulated anthocyanin pigment and turn a purple color. If C is present alone, the plant will remain green through out its life cycle despite environmental conditions. If both are present, however, the calyxes of the plant will also exhibit accumulated anthocyanin and turn purple as the leaves do. Let us assume for now that this may be a desirable trait in Cannabis flowers. What breeding techniques can be used to produce this trait? First, two homozygous true-breeding ~1 types are crossed and the phenotype ratio of the F1 offspring is observed. The phenotypes of the F2 progeny show a slightly altered phenotype ratio of 9:3:4 instead of the expected 9:3:3:1 for independently assorting traits. If P and C must both be present for any anthocyanin pigmentation in leaves or calyxes, then an even more distorted phenotype ratio of 9:7 will appear. Two gene pairs may interact in varying ways to pro duce varying phenotype ratios. Suddenly, the simple laws of inheritance have become more complex, but the data may still be interpreted.

Summary of Essential Points of Breeding

1 - The genotypes of plants are controlled by genes which are passed on unchanged from generation to generation. 
2 - Genes occur in pairs, one from the gamete of the staminate parent and one from the gamete of the pistillate parent. 
3 - When the members of a gene pair differ in their effect upon phenotype, the plant is termed hybrid or heterozygous. 
4 - When the members of a pair of genes are equal in their effect upon phenotype, then they are termed true-breeding or homozygous. 
5 - Pairs of genes controlling different phenotypic traits are (usually) inherited independently. 
6 - Dominance relations and gene interaction can alter the phenotypic ratios of the F1, F2, and subsequent generations.

Polyploidy

Polyploidy is the condition of multiple sets of chromosomes within one cell. Cannabis has 20 chromosomes in the vegetative diploid (2n) condition. Triploid (3n) and tetraploid (4n) individuals have three or four sets of chromosomes and are termed polyploids. It is believed that the haploid condition of 10 chromosomes was likely derived by reduction from a higher (polyploid) ancestral number (Lewis, W. H. 1980). Polyploidy has not been shown to occur naturally in Cannabis; however, it may be induced artificially with colchicine treatments. Colchicine is a poisonous compound extracted from the roots of certain Colchicum species; it inhibits chromosome segregation to daughter cells and cell wall formation, resulting in larger than average daughter cells with multiple chromosome sets. The studies of H. E. Warmke et al. (1942-1944) seem to indicate that colchicine raised drug levels in Cannabis. It is unfortunate that Warmke was unaware of the actual psychoactive ingredients of Cannabis and was therefore unable to extract THC. His crude acetone extract and archaic techniques of bioassay using killifish and small freshwater crustaceans are far from conclusive. He was, however, able to produce both triploid and tetraploid strains of Cannabis with up to twice the potency of dip bid strains (in their ability to kill small aquatic organisms). The aim of his research was to "produce a strain of hemp with materially reduced marijuana content" and his results indicated that polyploidy raised the potency of Cannabis without any apparent increase in fiber quality or yield. Warmke's work with polyploids shed light on the nature of sexual determination in Cannabis. He also illustrated that potency is genetically determined by creating a lower potency strain of hemp through selective breeding with low potency parents.

More recent research by A. I. Zhatov (1979) with fiber Cannabis showed that some economically valuable traits such as fiber quantity may be improved through polyploidy. Polyploids require more water and are usually more sensitive to changes in environment. Vegetative growth cycles are extended by up to 30-40% in polyploids. An extended vegetative period could delay the flowering of polyploid drug strains and interfere with the formation of floral clusters. It would be difficult to determine if cannabinoid levels had been raised by polyploidy if polyploid plants were not able to mature fully in the favorable part of the season when cannabinoid production is promoted by plentiful light and warm temperatures. Greenhouses and artificial lighting can be used to extend the season and test polyploid strains. The height of tetraploid (4n) Cannabis in these experiments often exceeded the height of the original diploid plants by 25-30%. Tetraploids were intensely colored, with dark green leaves and stems and a well developed gross phenotype. Increased height and vigorous growth, as a rule, vanish in subsequent generations. Tetraploid plants often revert back to the diploid condition, making it difficult to support tetraploid populations. Frequent tests are performed to determine if ploidy is changing. Triploid (3n) strains were formed with great difficulty by crossing artificially created tetraploids (4n) with dip bids (2n). Triploids proved to be inferior to both diploids and tetraploids in many cases.

De Pasquale et al. (1979) conducted experiments with Cannabis which was treated with 0.25% and 0.50% solutions of colchicine at the primary meristem seven days after generation. Treated plants were slightly taller and possessed slightly larger leaves than the controls, Anomalies in leaf growth occurred in 20% and 39%, respectively, of the surviving treated plants. In the first group (0.25%) cannabinoid levels were highest in the plants without anomalies, and in the second group (0.50%) cannabinoid levels were highest in plants with anomalies, Overall, treated plants showed a 166-250% increase in THC with respect to controls and a decrease of CBD (30-33%) and CBN (39-65%). CBD (cannabidiol) and CBN (cannabinol) are cannabinoids involved in the biosynthesis and degradation of THC. THC levels in the control plants were very low (less than 1%). Possibly colchicine or the resulting polyploidy interferes with cannabinoid biogenesis to favor THC. In treated plants with deformed leaf lamina, 90% of the cells are tetraploid (4n 40) and 10% diploid (2n 20). In treated plants without deformed lamina a few cells are tetraploid and the remainder are triploid or diploid. The transformation of diploid plants to the tetraploid level inevitably results in the formation of a few plants with an unbalanced set of chromosomes (2n + 1, 2n - 1, etc.). These plants are called aneuploids. Aneuploids are inferior to polyploids in every economic respect. Aneuploid Cannabis is characterized by extremely small seeds. The weight of 1,000 seeds ranges from 7 to 9 grams (1/4 to 1/3 ounce). Under natural conditions diploid plants do not have such small seeds and average 14-19 grams (1/2-2/3 ounce) per 1,000 (Zhatov 1979). Once again, little emphasis has been placed on the relationship between flower or resin production and polyploidy. Further research to determine the effect of polyploidy on these and other economically valuable traits of Cannabis is needed.

Colchicine is sold by laboratory supply houses, and breeders have used it to induce polyploidy in Cannabis. However, colchicine is poisonous, so special care is exercised by the breeder in any use of it. Many clandestine cultivators have started polyploid strains with colchicine. Except for changes in leaf shape and phyllotaxy, no out standing characteristics have developed in these strains and potency seems unaffected. However, none of the strains have been examined to determine if they are actually polyploid or if they were merely treated with colchicine to no effect. Seed treatment is the most effective and safest way to apply colchicine. * In this way, the entire plant growing from a colchicine-treated seed could be polyploid and if any colchicine exists at the end of the growing season the amount would be infinitesimal. Colchicine is nearly always lethal to Cannabis seeds, and in the treatment there is a very fine line between polyploidy and death. In other words, if 100 viable seeds are treated with colchicine and 40 of them germinate it is unlikely that the treatment induced polyploidy in any of the survivors. On the other hand, if 1,000 viable treated seeds give rise to 3 seedlings, the chances are better that they are polyploid since the treatment killed all of the seeds but those three. It is still necessary to determine if the offspring are actually polyploid by microscopic examination.

The work of Menzel (1964) presents us with a crude map of the chromosomes of Cannabis, Chromosomes 2-6 and 9 are distinguished by the length of each arm. Chromosome 1 is distinguished by a large knob on one end and a dark chromomere 1 micron from the knob. Chromosome 7 is extremely short and dense, and chromosome 8 is assumed to be the sex chromosome. In the future, chromosome *The word "safest" is used here as a relative term. Coichicine has received recent media attention as a dangerous poison and while these accounts are probably a bit too lurid, the real dangers of exposure to coichicine have not been fully researched. The possibility of bodily harm exists and this is multiplied when breeders inexperienced in handling toxins use colchicine. Seed treatment might be safer than spraying a grown plant but the safest method of all is to not use colchicine. mapping will enable us to picture the location of the genes influencing the phenotype of Cannabis. This will enable geneticists to determine and manipulate the important characteristics contained in the gene pool. For each trait the number of genes in control will be known, which chromosomes carry them, and where they are located along those chromosomes.

Breeding

All of the Cannabis grown in North America today originated in foreign lands. The diligence of our ancestors in their collection and sowing of seeds from superior plants, together with the forces of natural selection, have worked to create native strains with localized characteristics of resistance to pests, diseases, and weather conditions. In other words, they are adapted to particular niches in the ecosystem. This genetic diversity is nature's way of protecting a species. There is hardly a plant more flexible than Cannabis. As climate, diseases, and pests change, the strain evolves and selects new defenses, programmed into the genetic orders contained in each generation of seeds. Through the importation in recent times of fiber and drug Cannabis, a vast pool of genetic material has appeared in North America. Original fiber strains have escaped and become acclimatized (adapted to the environment), while domestic drug strains (from imported seeds) have, unfortunately, hybridized and acclimatized randomly, until many of the fine gene combinations of imported Cannabis have been lost.

Changes in agricultural techniques brought on by technological pressure, greed, and full-scale eradication programs have altered the selective pressures influencing Cannabis genetics. Large shipments of inferior Cannabis containing poorly selected seeds are appearing in North America and elsewhere, the result of attempts by growers and smugglers to supply an ever increasing market for marijuana. Older varieties of Cannabis, associated with long standing cultural patterns, may contain genes not found in the newer commercial varieties. As these older varieties and their corresponding cultures become extinct, this genetic information could be lost forever. The increasing popularity of Cannabis and the requirements of agricultural technology will call for uniform hybrid races that are likely to displace primitive populations worldwide. Limitation of genetic diversity is certain to result from concerted inbreeding for uniformity. Should inbred Cannabis be attacked by some previously unknown pest or disease, this genetic uniformity could prove disastrous due to potentially resistant diverse genotypes having been dropped from the population. If this genetic complement of resistance cannot be reclaimed from primitive parental material, resistance cannot be introduced into the ravaged population. There may also be currently unrecognized favorable traits which could be irretrievably dropped from the Cannabis gene pool. Human intervention can create new phenotypes by selecting and recombining existing genetic variety, but only nature can create variety in the gene pool itself, through the slow process of random mutation.

This does not mean that importation of seed and selective hybridization are always detrimental. Indeed these principles are often the key to crop improvement, but only when applied knowledgeably and cautiously. The rapid search for improvements must not jeopardize the pool of original genetic information on which adaptation relies. At this time, the future of Cannabis lies in government and clandestine collections. These collections are often inadequate, poorly selected and badly maintained. Indeed, the United Nations Cannabis collection used as the primary seed stock for worldwide governmental research is depleted and spoiled. Several steps must be taken to preserve our vanishing genetic resources, and action must be immediate: Seeds and pollen should be collected directly from reliable and knowledgeable sources. Government seizures and smuggled shipments are seldom reliable seed sources. The characteristics of both parents must be known; consequently, mixed bales of randomly pollinated marijuana are not suitable seed sources, even if the exact origin of the sample is certain. Direct contact should be made with the farmer-breeder responsible for carrying on the breeding traditions that have produced the sample. Accurate records of every possible parameter of growth must be kept with carefully stored triplicate sets of seeds. Since Cannabis seeds do not remain viable forever, even under the best storage conditions, seed samples should he replenished every third year. Collections should be planted in conditions as similar as possible to their original niche and allowed to reproduce freely to minimize natural and artificial selection of genes and ensure the preservation of the entire gene pool. Half of the original seed collection should be retained until the viability of further generations is confirmed, and to provide parental material for comparison and back-crossing. Phenotypic data about these subsequent generations should be carefully recorded to aid in understanding the genotypes contained in the collection. Favorable traits of each strain should be characterized and catalogued.

It is possible that in the future, Cannabis cultivation for resale, or even personal use, may be legal but only for approved, patented strains. Special caution would be needed to preserve variety in the gene pool should the patenting of Cannabis strains become a reality. Favorable traits must be carefully integrated into existing strains. The task outlined above is not an easy one, given the current legal restrictions on the collection of Cannabis seed. In spite of this, the conscientious cultivator is making a contribution toward preserving and improving the genetics of this interesting plant. Even if a grower has no desire to attempt crop improvement, successful strains have to be protected so they do not degenerate and can be reproduced if lost. Left to the selective pressures of an introduced environment, most drug strains will degenerate and lose potency as they acclimatize to the new conditions. Let me cite an example of a typical grower with good intentions. A grower in northern latitudes selected an ideal spot to grow a crop and prepared the soil well. Seeds were selected from the best floral clusters of several strains avail able over the past few years, both imported and domestic. Nearly all of the staminate plants were removed as they matured and a nearly seedless crop of beautiful plants resulted. After careful consideration, the few seeds from accidental pollination of the best flowers were kept for the following season, These seeds produced even bigger and better plants than the year before and seed collection was performed as before. The third season, most of the plants were not as large or desirable as the second season, but there were many good individuals. Seed collection and cultivation the fourth season resulted in plants inferior even to the first crop, and this trend continued year after year. What went wrong? The grower collected seed from the best plants each year and grew them under the same conditions. The crop improved the first year. Why did the strain degenerate?

This example illustrates the unconscious selection for undesirable traits. The hypothetical cultivator began well by selecting the best seeds available and growing them properly. The seeds selected for the second season resulted from random hybrid pollinations by early-flowering or overlooked staminate plants and by hermaphrodite pistil late plants. Many of these random pollen-parents may be undesirable for breeding since they may pass on tendencies toward premature maturation, retarded maturation, or hermaphrodism. However, the collected hybrid seeds pro duce, on the average, larger and more desirable offspring than the first season. This condition is called hybrid vigor and results from the hybrid crossing of two diverse gene pools. The tendency is for many of the dominant characteristics from both parents to be transmitted to the F1 off spring, resulting in particularly large and vigorous plants. This increased vigor due to recombination of dominant genes often raises the cannabinoid level of the F1 offspring, but hybridization also opens up the possibility that undesirable (usually recessive) genes may form pairs and express their characteristics in the F2 offspring. Hybrid vigor may also mask inferior qualities due to abnormally rapid growth. During the second season, random pollinations again accounted for a few seeds and these were collected. This selection draws on a huge gene pool and the possible F2 combinations are tremendous. By the third season the gene pool is tending toward early-maturing plants that are acclimatized to their new conditions instead of the drug-producing conditions of their native environment. These acclimatized members of the third crop have a higher chance of maturing viable seeds than the parental types, and random pollinations will again increase the numbers of acclimatized individuals, and thereby increase the chance that undesirable characteristics associated with acclimatization will be transmitted to the next F2 generation. This effect is compounded from generation to generation and finally results in a fully acclimatized weed strain of little drug value.

With some care the breeder can avoid these hidden dangers of unconscious selection. Definite goals are vital to progress in breeding Cannabis. What qualities are desired in a strain that it does not already exhibit? What characteristics does a strain exhibit that are unfavorable and should be bred out? Answers to these questions suggest goals for breeding. In addition to a basic knowledge of Cannabis botany, propagation, and genetics, the successful breeder also becomes aware of the most minute differences and similarities in phenotype. A sensitive rapport is established between breeder and plants and at the same time strict guidelines are followed. A simplified explanation of the time-tested principles of plant breeding shows how this works in practice. Selection is the first and most important step in the breeding of any plant. The work of the great breeder and plant wizard Luther Burbank stands as a beacon to breeders of exotic strains. His success in improving hundreds of flower, fruit, and vegetable crops was the result of his meticulous selection of parents from hundreds of thou sands of seedlings and adults from the world over. Bear in mind that in the production of any new plant, selection plays the all-important part. First, one must get clearly in mind the kind of plant he wants, then breed and select to that end, always choosing through a series of years the plants which are approaching nearest the ideal, and rejecting all others. Proper selection of prospective parents is only possible if the breeder is familiar with the variable characteristics of Cannabis that may be genetically controlled, has a way to accurately measure these variations, and has established goals for improving these characteristics by selective breeding. A detailed list of variable traits of Cannabis, including parameters of variation for each trait and comments pertaining to selective breeding for or against it, are found at the end of this chapter. By selecting against unfavorable traits while selecting for favorable ones, the unconscious breeding of poor strains is avoided.

The most important part of Burbank's message on selection tells breeders to choose the plants "which are approaching nearest the ideal," and REJECT ALL OTHERS! Random pollinations do not allow the control needed to reject the undesirable parents. Any staminate plant that survives detection and roguing (removal from the population), or any stray staminate branch on a pistillate her maphrodite may become a pollen parent for the next generation. Pollination must be controlled so that only the pollen- and seed-parents that have been carefully selected for favorable traits will give rise to the next generation. Selection is greatly improved if one has a large sample to choose from! The best plant picked from a group of 10 has far less chance of being significantly different from its fellow seedlings than the best plant selected from a sample of 100,000. Burbank often made his initial selections of parents from samples of up to 500,000 seedlings. Difficulties arise for many breeders because they lack the space to keep enough examples of each strain to allow a significant selection. A Cannabis breeder's goals are restricted by the amount of space available. Formulating a well defined goal lowers the number of individuals needed to perform effective crosses. Another technique used by breeders since the time of Burbank is to make early selections. Seedling plants take up much less space than adults. Thousands of seeds can be germinated in a flat. A flat takes up the same space as a hundred 10-centimeter (4-inch) sprouts or six-teen 30-centimeter (12-inch) seedlings or one 60-centimeter (24-inch) juvenile. An adult plant can easily take up as much space as a hundred flats. Simple arithmetic shows that as many as 10,000 sprouts can be screened in the space required by each mature plant, provided enough seeds are available. Seeds of rare strains are quite valuable and exotic; however, careful selection applied to thousands of individuals, even of such common strains as those from Colombia or Mexico, may produce better offspring than plants from a rare strain where there is little or no opportunity for selection after germination. This does not mean that rare strains are not valuable, but careful selection is even more important to successful breeding. The random pollinations that produce the seeds in most imported marijuana assure a hybrid condition which results in great seed ling diversity. Distinctive plants are not hard to discover if the seedling sample is large enough.

Traits considered desirable when breeding Cannabis often involve the yield and quality of the final product, but these characteristics can only be accurately measured after the plant has been harvested and long after it is possible to select or breed it. Early seedling selection, therefore, only works for the most basic traits. These are selected first, and later selections focus on the most desirable characteristics exhibited by juvenile or adult plants. Early traits often give clues to mature phenotypic expression, and criteria for effective early seedling selection are easy to establish. As an example, particularly tall and thin seedlings might prove to be good parents for pulp or fiber production, while seed lings of short internode length and compound branching may be more suitable for flower production. However, many important traits to be selected for in Cannabis floral clusters cannot be judged until long after the parents are gone, so many crosses are made early and selection of seeds made at a later date. Hybridization is the process of mixing differing gene pools to produce offspring of great genetic variation from which distinctive individuals can be selected. The wind performs random hybridization in nature. Under cultivation, breeders take over to produce specific, controlled hybrids. This process is also known as cross-pollination, cross-fertilization, or simply crossing. If seeds result, they will produce hybrid offspring exhibiting some characteristics from each parent. Large amounts of hybrid seed are most easily produced by planting two strains side by side, removing the staininate plants of the seed strain, and allowing nature to take its course. Pollen- or seed-sterile strains could be developed for the production of large amounts of hybrid seed without the labor of thinning; however, genes for sterility are rare. It is important to remember that parental weak nesses are transmitted to offspring as well as strengths. Because of this, the most vigorous, healthy plants are al ways used for hybrid crosses.

Also, sports (plants or parts of plants carrying and expressing spontaneous mutations) most easily transmit mutant genes to the offspring if they are used as pollen parents. If the parents represent diverse gene pools, hybrid vigor results, because dominant genes tend to carry valuable traits and the differing dominant genes inherited from each parent mask recessive traits inherited from the other. This gives rise to particularly large, healthy individuals. To increase hybrid vigor in offspring, parents of different geo graphic origins are selected since they will probably represent more diverse gene pools. Occasionally hybrid offspring will prove inferior to both parents, but the first generation may still contain recessive genes for a favorable characteristic seen in a parent if the parent was homozygous for that trait. First generation (F1) hybrids are therefore inbred to allow recessive genes to recombine and express the desired parental trait. Many breeders stop with the first cross and never realize the genetic potential of their strain. They fail to produce an F2 generation by crossing or self-pollinating F1 offspring. Since most domestic Cannabis strains are F1 hybrids for many characteristics, great diversity and recessive recombination can result from inbreeding domestic hybrid strains. In this way the breeding of the F1 hybrids has already been accomplished, and a year is saved by going directly to F2 hybrids. These F2 hybrids are more likely to express recessive parental traits. From the F2 hybrid generation selections can be made for parents which are used to start new true-breeding strains. Indeed, F2 hybrids might appear with more extreme characteristics than either of the P~ parents. (For example, P1 high-THC X P1 low-THC yields F1 hybrids of intermediate THC content. Selfing the F1 yields F2 hybrids, of both P1 [high and low THC] phenotypes, inter mediate F1 phenotypes, and extra-high THC as well as extra-low THC phenotypes.)

Also, as a result of gene recombination, F1 hybrids are not true-breeding and must be reproduced from the original parental strains. When breeders create hybrids they try to produce enough seeds to last for several successive years of cultivation, After initial field tests, undesirable hybrid seeds are destroyed and desirable hybrid seeds stored for later use. If hybrids are to be reproduced, a clone is saved from each parental plant to preserve original parental genes. Back-crossing is another technique used to produce offspring with reinforced parental characteristics. In this case, a cross is made between one of the F~ or subsequent offspring and either of the parents expressing the desired trait. Once again this provides a chance for recombination and possible expression of the selected parental trait. Back-crossing is a valuable way of producing new strains, but it is often difficult because Cannabis is an annual, so special care is taken to save parental stock for back-crossing the following year. Indoor lighting or greenhouses can be used to protect breeding stock from winter weather. In tropical areas plants may live outside all year. In addition to saving particular parents, a successful breeder always saves many seeds from the original P1 group that produced the valuable characteristic so that other P1 plants also exhibiting the characteristic can be grown and selected for back-crossing at a later time.

Several types of breeding are summarized as follows:

1 - Crossing two varieties having outstanding qualities (hybridization). 
2 - Crossing individuals from the F1 generation or selfing F1 individuals to realize the possibilities of the original cross (differentiation). 
3 - Back crossing to establish original parental types. 
4 - Crossing two similar true-breeding (homozygous) varieties to preserve a mutual trait and restore vigor.

It should be noted that a hybrid plant is not usually hybrid for all characteristics nor does a true-breeding strain breed true for all characteristics. When discussing crosses, we are talking about the inheritance of one or a few traits only. The strain may be true-breeding for only a few traits, hybrid for the rest. Monohybrid crosses involve one trait, dihybrid crosses involve two traits, and so forth. Plants have certain limits of growth, and breeding can only pro duce a plant that is an expression of some gene already present in the total gene pool. Nothing is actually created by breeding; it is merely the recombination of existing genes into new genotypes. But the possibilities of recombination are nearly limitless. 
The most common use of hybridization is to cross two outstanding varieties. Hybrids can be produced by crossing selected individuals from different high-potency strains of different origins, such as Thailand and Mexico. These two parents may share only the characteristic of high psycho activity and differ in nearly every other respect. From this great exchange of genes many phenotypes may appear in the F2 generation. From these offspring the breeder selects individuals that express the best characteristics of the parents. As an example, consider some of the offspring from the P1 (parental) cross: Mexico X Thailand. In this case, genes for high drug content are selected from both parents while other desirable characteristics can be selected from either one. Genes for large stature and early maturation are selected from the Mexican seed-parent, and genes for large calyx size and sweet floral aroma are selected from the Thai pollen parent. Many of the F1 offspring exhibit several of the desired characteristics. To further promote gene segregation, the plants most nearly approaching the ideal are crossed among themselves. The F2 generation is a great source of variation and recessive expression. In the F2 generation there are several individuals out of many that exhibit all five of the selected characteristics. Now the process of inbreeding begins, using the desirable F2 parents.

If possible, two or more separate lines are started, never allowing them to interbreed. In this case one accept able staminate plant is selected along with two pistillate plants (or vice versa). Crosses between the pollen parent and the two seed parents result in two lines of inheritance with slightly differing genetics, but each expressing the desired characteristics. Each generation will produce new, more acceptable combinations. If two inbred strains are crossed, F1 hybrids will be less variable than if two hybrid strains are crossed. This comes from limiting the diversity of the gene pools in the two strains to be hybridized through previous inbreeding. Further independent selection and inbreeding of the best plants for several generations will establish two strains which are true-breeding for all the originally selected traits. This means that all the offspring from any parents in the strain will give rise to seedlings which all exhibit the selected traits. Successive inbreeding may by this time have resulted in steady decline in the vigor of the strain. When lack of vigor interferes with selecting phenotypes for size and hardiness, the two separately selected strains can then be interbred to recombine nonselected genes and restore vigor. This will probably not interfere with breeding for the selected traits unless two different gene systems control the same trait in the two separate lines, and this is highly unlikely. Now the breeder has produced a hybrid strain that breeds true for large size, early maturation, large sweet-smelling calyxes, and high THC level. The goal has been reached!

Wind pollination and dioecious sexuality favor a heterozygous gene pool in Cannabis. Through Anbreeding, hybrids are adapted from a heterozygous gene pool to a homozygous gene pool, providing the genetic stability needed to create true-breeding strains. Establishing pure strains enables the breeder to make hybrid crosses with a better chance of predicting the outcome. Hybrids can be created that are not reproducible in the F2 generation. Commercial strains of seeds could be developed that would have to be purchased each year, because the F1 hybrids of two pure-bred lines do not breed true. Thus, a seed breeder can protect the investment in the results of breeding, since it would be nearly impossible to reproduce the parents from F2 seeds. At this time it seems unlikely that a plant patent would be awarded for a pure-breeding strain of drug Cannabis. In the future, however, with the legalization of cultivation, it is a certainty that corporations with the time, space, and money to produce pure and hybrid strains of Cannabis will apply for patents. It may be legal to grow only certain patented strains produced by large seed companies. Will this be how government and industry combine to control the quality and quantity of "drug" Cannabis?

Acclimatization

Much of the breeding effort of North American cultivators is concerned with acclimatizing high-THC strains of equatorial origin to the climate of their growing area while preserving potency. Late-maturing, slow, and irregularly flowering strains like those of Thailand have difficulty maturing in many parts of North America. Even in a green house, it may not be possible to mature plants to their full native potential. To develop an early-maturing and rapidly flowering 8train, a breeder may hybridize as in the previous example. However, if it is important to preserve unique imported genetics, hybridizing may be inadvisable. Alternatively, a pure cross is made between two or more Thai plants that most closely approach the ideal in blooming early. At this point the breeder may ignore many other traits and aim at breeding an earlier-maturing variety of a pure Thai strain. This strain may still mature considerably later than is ideal for the particular location unless selective pressure is exerted. If further crosses are made with several individuals that satisfy other criteria such as high THC content, these may be used to develop another pure Thai strain of high THC content. After these true-breeding lines have been established, a dihybrid pure cross can be made in an attempt to produce an F1 generation containing early-maturing, high-THC strains of pure Thai genetics, in other words, an acclimatized drug strain. Crosses made without a clear goal in mind lead to strains that acclimatize while losing many favorable characteristics. A successful breeder is careful not to overlook a characteristic that may prove useful. It is imperative that original imported Cannabis genetics be preserved intact to protect the species from loss of genetic variety through excessive hybridization. A currently unrecognized gene may be responsible for controlling resistance to a pest or disease, and it may only be possible to breed for this gene by back-crossing existing strains to original parental gene pools. Once pure breeding lines have been established, plant breeders classify and statistically analyze the offspring to determine the patterns of inheritance for that trait. 

This is the system used by Gregor Mendel to formulate the basic laws of inheritance and aid the modern breeder in predicting the outcome of crosses,

1 - Two pure lines of Cannabis that differ in a particular trait are located. 
2 - These two pure-breeding lines are crossed to pro duce an F1 generation. 
3 - The F1 generation is inbred. 
4 - The offspring of the F1 and F2 generations are classified with regard to the trait being studied. 
5 - The results are analyzed statistically. 
6 - The results are compared to known patterns of inheritance so the nature of the genes being selected for can be characterized.

Fixing Traits

Fixing traits (producing homozygous offspring) in Cannabis strains is more difficult than it is in many other flowering plants. With monoecious strains or hermaphrodites it is possible to fix traits by self-pollinating an individual exhibiting favorable traits. In this case one plant acts as both mother and father. However, most strains of Cannabis are dioecious, and unless hermaphroditic reactions can be induced, another parent exhibiting the trait is required to fix the trait. If this is not possible, the unique individual may be crossed with a plant not exhibiting the trait, inbred in the F1 generation, and selections of parents exhibiting the favorable trait made from the F2 generation, but this is very difficult. If a trait is needed for development of a dioecious strain it might first be discovered in a monoecious strain and then fixed through selfing and selecting homozygous offspring. Dioecious individuals can then be selected from the monoecious population and these individuals crossed to breed out monoecism in subsequent generations.

Galoch (197 indicated that gibberellic acid (GA3) promoted stamen production while indoleacetic acid (IAA), ethrel, and kinetin promoted pistil production in prefloral dioecious Cannabis. Sex alteration has several useful applications. Most importantly, if only one parent expressing a desirable trait can be found, it is difficult to perform a cross unless it happens to be a hermaphrodite plant. Hormones might be used to change the sex of a cutting from the desirable plant, and this cutting used to mate with it. This is most easily accomplished by changing a pistillate cutting to a staminate (pollen) parent, using a spray of 100 ppm gibberellic acid in water each day for five consecutive days. Within two weeks staminate flowers may appear. Pollen can then be collected for selfing with the original pistillate parent. Offspring from the cross should also be mostly pistillate since the breeder is selfing for pistillate sexuality. Staminate parents reversed to pistillate floral production make inferior seed-parents since few pistillate flowers and seeds are formed. If entire crops could be manipulated early in life to produce all pistillate or staminate plants, seed production and seedless drug Cannabis production would be greatly facilitated. Sex reversal for breeding can also be accomplished by mutilation and by photoperiod alteration. A well-rooted, flourishing cutting from the parent plant is pruned back to 25% of its original size and stripped of all its remaining flowers. New growth will appear within a few days, and several flowers of reversed sexual type often appear. Flowers of the unwanted sex are removed until the cutting is needed for fertilization. Extremely short light cycles (6-8 hour photoperiod) can also cause sex reversal. How ever, this process takes longer and is much more difficult to perform in the field.

Genotype and Phenotype Ratios

It must be remembered, in attempting to fix favorable characteristics, that a monohybrid cross gives rise to four possible recombinant genotypes, a dihybrid cross gives rise to 16 possible recombinant genotypes, and so forth. Phenotype and genotype ratios are probabilistic. If recessive genes are desired for three traits it is not effective to raise only 64 offspring and count on getting one homozygous recessive individual. To increase the probability of success it is better to raise hundreds of offspring, choosing only the best homozygous recessive individuals as future parents. All laws of inheritance are based on chance and offspring may not approach predicted ratios until many more have been phenotypically characterized and grouped than the theoretical minimums.

The genotype of each individual is expressed by a mosaic of thousands of subtle overlapping traits. It is the sum total of these traits that determines the general phenotype of an individual. It is often difficult to determine if the characteristic being selected is one trait or the blending of several traits and whether these traits are controlled by one or several pairs of genes. It often makes little difference that a breeder does not have plants that are proven to breed true. Breeding goals can still be established. The selfing of F1 hybrids will often give rise to the variation needed in the F2 generation for selecting parents for subsequent generations, even if the characteristics of the original parents of the F1 hybrid are not known. It is in the following generations that fixed characteristics appear and the breeding of pure strains can begin. By selecting and crossing individuals that most nearly approach the ideal described by the breeding goals, the variety can be continuously improved even if the exact patterns of inheritance are never deter mined. Complementary traits are eventually combined into one line whose seeds reproduce the favorable parental traits. Inbreeding strains also allows weak recessive traits to express themselves and these abnormalities must be diligently removed from the breeding population. After five or six generations, strains become amazingly uniform. Vigor is occasionally restored by crossing with other lines or by backcrossing. Parental plants are selected which most nearly approach the ideal. If a desirable trait is not expressed by the parent, it is much less likely to appear in the offspring. It is imperative that desirable characteristics be hereditary and not primarily the result of environment and cultivation. Acquired traits are not hereditary and cannot be made hereditary. Breeding for as few traits as possible at one time greatly increases the chance of success. In addition to the specific traits chosen as the aims of breeding, parents are selected which possess other generally desirable traits such as vigor and size. Determinations of dominance and recessiveness can only be made by observing the outcome of many crosses, although wild traits often tend to be dominant. This is one of the keys to adaptive survival. However, all the possible combinations will appear in the F2 generation if it is large enough, regardless of dominance. 

Now, after further simplifying this wonderful system of inheritance, there are additional exceptions to the rules which must be explored. In some cases, a pair of genes may control a trait but a second or third pair of genes is needed to express this trait. This is known as gene inter action. No particular genetic attribute in which we may be interested is totally isolated from other genes and the effects of environment. Genes are occasionally transferred in groups instead of assorting independently. This is known as gene linkage, These genes are spaced along the same chromosome and may or may not control the same trait. The result of linkage might be that one trait cannot be inherited without another. At times, traits are associated with the X and Y sex chromosomes and they may be limited to expression in only one sex (sex linkage). Crossing over also interferes with the analysis of crosses. Crossing over is the exchanging of entire pieces of genetic material between two chromosomes. This can result in two genes that are normally linked appearing on separate chromosomes where they will be independently inherited. All of these processes can cause crosses to deviate from the expected Mendelian outcome. Chance is a major factor in breeding Cannabis, or any introduced plant, and the more crosses a breeder attempts the higher are the chances of success. Variate, isolate, intermate, evaluate, multiplicate, and disseminate are the key words in plant improvement. A plant breeder begins by producing or collecting various prospective parents from which the most desirable ones are selected and isolated. Intermating of the select parents results in offspring which must be evaluated for favorable characteristics. If evaluation indicates that the offspring are not improved, then the process is repeated. Improved off spring are multiplied and disseminated for commercial use. Further evaluation in the field is necessary to check for uniformity and to choose parents for further intermating. This cyclic approach provides a balanced system of plant improvement.

The basic nature of Cannabis makes it challenging to breed. Wind pollination and dioecious sexuality, which account for the great adaptability in Cannabis, cause many problems in breeding, but none of these are insurmountable. Developing a knowledge and feel for the plant is more important than memorizing Mendelian ratios. The words of the great Luther Burbank say it well, "Heredity is indelibly fixed by repetition." The first set of traits concerns Cannabis plants as a whole while the remainder concern the qualities of seedlings, leaves, fibers, and flowers. Finally a list of various Cannabis strains is provided along with specific characteristics. Following this order, basic and then specific selections of favorable characteristics can be made.

List of Favorable Traits of Cannabis in Which Variation Occurs

1. General Traits: 

a) Size and Yield
b) Vigor
c) Adaptability
d) Hardiness
e) Disease and Pest Resistance
f) Maturation
g) Root Production
h) Branching
i) Sex

2. Seedling Traits
3. Leaf Traits
4. Fiber Traits
5. Floral Traits: 

a) Shape
b) Form
c) Calyx Size
d) Color
e) Cannabinoid Level
f) Taste and Aroma
g) Persistence of Aromatic Principles and Cannabinoids
h) Trichome Type
i) Resin Quantity and Quality
j) Resin Tenacity
k) Drying and Curing Rate
I) Ease of Manicuring
m) Seed Characteristics
n) Maturation
o) Flowering
p) Ripening
q) Cannabinoid Profile

6. Gross Phenotypes

1. General Traits

a) Size and Yield - The size of an individual Cannabis plant is determined by environmental factors such as room for root and shoot growth, adequate light and nutrients, and proper irrigation. These environmental factors influence the phenotypic image of genotype, but the genotype of the individual is responsible for overall variations in gross morphology, including size. Grown under the same conditions, particularly large and small individuals are easily spotted and selected. Many dwarf Cannabis plants have been re ported and dwarfism may be subject to genetic control, as it is in many higher plants, such as dwarf corn and citrus. Cannabis parents selected for large size tend to produce offspring of a larger average size each year. Hybrid crosses between tall (Cannabis sativa-Mexico) strains and short (Cannabis ruderalis-Russia) strains yield F1 offspring of intermediate height (Beutler and der Marderosian 197. Hybrid vigor, however, will influence the size of offspring more than any other genetic factor. The increased size of hybrid offspring is often amazing and accounts for much of the success of Cannabis cultivators in raising large plants. It is not known whether there is a set of genes for "gigantism" in Cannabis or whether polyploid individuals really yield more than diploid due to increased chromosome count. Tetraploids tend to be taller and their water re quirements are often higher than diploids. Yield is determined by the overall production of fiber, seed, or resin and selective breeding can be used to increase the yield of any one of these products. However, several of these traits may be closely related, and it may be impossible to breed for one without the other (gene linkage). Inbreeding of a pure strain increases yield only if high yield parents are selected. High yield plants, staminate or pistillate, are not finally selected until the plants are dried and manicured. Because of this, many of the most vigorous plants are crossed and seeds selected after harvest when the yield can be measured.

b) Vigor - Large size is often also a sign of healthy vigorous growth. A plant that begins to grow immediately will usually reach a larger size and produce a higher yield in a short growing season than a sluggish, slow-growing plant. Parents are always selected for rich green foliage and rapid, responsive growth. This will ensure that genes for certain weaknesses in overall growth and development are bred out of the population while genes for strength and vigor remain.

c) Adaptability - It is important for a plant with a wide distribution such as Cannabis to be adaptable to many different environmental conditions. Indeed, Cannabis is one of the most genotypically diverse and phenotypically plastic plants on earth; as a result it has adapted to environ mental conditions ranging from equatorial to temperate climates. Domestic agricultural circumstances also dictate that Cannabis must be grown under a great variety of conditions, Plants to be selected for adaptability are cloned and grown in several locations. The parental stocks with the highest survival percentages can be selected as prospective parents for an adaptable strain. Adaptability is really just another term for hardiness under varying growth conditions.

d) Hardiness - The hardiness of a plant is its overall resistance to heat and frost, drought and overwatering, and so on. Plants with a particular resistance appear when adverse conditions lead to the death of the rest of a large population. The surviving few members of the population might carry inheritable resistance to the environmental factor that destroyed the majority of the population. Breeding these survivors, subjecting the offspring to continuing stress conditions, and selecting carefully for several generations should result in a pure-breeding strain with increased resistance to drought, frost, or excessive heat.

e) Disease and Pest Resistance - In much the same way as for hardiness a strain may be bred for resistance to a certain disease, such as damping-off fungus. If flats of seedlings are infected by damping-off disease and nearly all of them die, the remaining few will have some resistance to damping-off fungus. If this resistance is inheritable, it can be passed on to subsequent generations by crossing these surviving plants. Subsequent crossing, tested by inoculating flats of seedling offspring with damping-off fungus, should yield a more resistant strain. Resistance to pest attack works in much the same way. It is common to find stands of Cannabis where one or a few plants are infested with insects while adjacent plants are untouched. Cannabinoid and terpenoid resins are most probably responsible for repelling insect attack, and levels of these vary from plant to plant. Cannabis has evolved defenses against insect attack in the form of resin-secreting glandular trichomes, which cover the reproductive and associated vegetative structures of mature plants. Insects, finding the resin disagreeable, rarely attack mature Cannabis flowers. However, they may strip the outer leaves of the same plant because these develop fewer glandular tri chomes and protective resins than the flowers. Non-glandular cannabinoids and other compounds produced within leaf and stem tissues which possibly inhibit insect attack, may account for the varying resistance of seedlings and vegetative juvenile plants to pest infestation. With the popularity of greenhouse Cannabis cultivation, a strain is needed with increased resistance to mold, mite, aphid,- or white fly infestation. These problems are often so severe that greenhouse cultivators destroy any plants which are attacked. Molds usually reproduce by wind-borne spores, so negligence can rapidly lead to epidemic disaster. Selection and breeding of the least infected plants should result in strains with increased resistance.

f) Maturation - Control of the maturation of Cannabis is very important no matter what the reason for growing it. If Cannabis is to be grown for fiber it is important that the maximum fiber content of the crop be reached early and that all of the individuals in the crop mature at the same time to facilitate commercial harvesting. Seed production requires the even maturation of both pollen and seed parents to ensure even setting and maturation of seeds. An uneven maturation of seeds would mean that some seeds would drop and be lost while others are still ripening. An understanding of floral maturation is the key to the production of high quality drug Cannabis. Changes in gross morphology are accompanied by changes in cannabinoid and terpenoid production and serve as visual keys to deter mining the ripeness of Cannabis flowers. A Cannabis plant may mature either early or late, be fast or slow to flower, and ripen either evenly or sequentially. Breeding for early or late maturation is certainly a reality; it is also possible to breed for fast or slow flowering and even or sequential ripening. In general, crosses between early-maturing plants give rise to early-maturing offspring, crosses between late-maturing plants give rise to late-maturing offspring, and crosses between late- and early-maturing plants give rise to offspring of intermediate maturation. This seems to indicate that maturation of Cannabis is not controlled by the simple dominance and recessiveness of one gene but probably results from incomplete dominance and a combination of genes for separate aspects of maturation. For instance, Sorghum maturation is controlled by four separate genes. The sum of these genes produces a certain phenotype for maturation. Al though breeders do not know the action of each specific gene, they still can breed for the total of these traits and achieve results more nearly approaching the goal of timely maturation than the parental strains.

g) Root Production - The size and shape of Cannabis root systems vary greatly. Although every embryo sends out a taproot from which lateral roots grow, the individual growth pattern and final size and shape of the roots vary considerably. Some plants send out a deep taproot, up to 1 meter (39 inches) long, which helps support the plant against winds and rain. Most Cannabis plants, however, produce a poor taproot which rarely extends more than 30 centimeters (1 foot). Lateral growth is responsible for most of the roots in Cannabis plants. These fine lateral roots offer the plant additional support but their primary function is to absorb water and nutrients from the soil. A large root system will be able to feed and support a large plant. Most lateral roots grow near the surface of the soil where there is more water, more oxygen, and more avail able nutrients. Breeding for root size and shape may prove beneficial for the production of large rain- and wind-resistant strains. Often Cannabis plants, even very large ones, have very small and sensitive root systems. Recently, certain alkaloids have been discovered in the roots of Cannabis that might have some medical value. If this proves the case, Cannabis may be cultivated and bred for high alkaloid levels in the roots to be used in the commercial production of pharmaceuticals. As with many traits, it is difficult to make selections for root types until the parents are harvested. Because of this many crosses are made early and seeds selected later.

h) Branching - The branching pattern of a Cannabis plant is determined by the frequency of nodes along each branch and the extent of branching at each node. For examples, consider a tall, thin plant with slender limbs made up of long internodes and nodes with little branching (Oaxaca, Mexico strain). Compare this with a stout, densely branched plant with limbs of short internodes and highly branched nodes (Hindu Kush hashish strains). Different branching patterns are preferred for the different agricultural applications of fiber, flower, or resin production. Tall, thin plants with long internodes and no branching are best adapted to fiber production; a short, broad plant with short inter nodes and well developed branching is best adapted to floral production. Branching structure is selected that will tolerate heavy rains and high winds without breaking. This is quite advantageous to outdoor growers in temperate zones with short seasons. Some breeders select tall, limber plants (Mexico) which bend in the wind; others select short, stiff plants (Hindu Kush) which resist the weight of water without bending.

i) Sex - Attempts to breed offspring of only one sexual type have led to more misunderstanding than any other facet of Cannabis genetics. The discoveries of McPhee (1925) and Schaffner (192 showed that pure sexual type and hermaphrodite conditions are inherited and that the percentage of sexual types could be altered by crossing with certain hermaphrodites. Since then it has generally been assumed by researchers and breeders that a cross between ANY unselected hermaphrodite plant and a pistillate seed-parent should result in a population of all pistillate offspring. This is not the case. In most cases, the offspring of hermaphrodite parents tend toward hermaphrodism, which is largely unfavorable for the production of Cannabis other than fiber hemp. This is not to say that there is no tendency for hermaphrodite crosses to alter sex ratios in the offspring. The accidental release of some pollen from predominantly pistillate hermaphrodites, along with the complete eradication of nearly every staminate and staminate hermaphrodite plant may have led to a shift in sexual ratio in domestic populations of sinsemilla drug Cannabis. It is commonly observed that these strains tend toward 60% to 80% pistillate plants and a few pistillate hermaphrodites are not uncommon in these populations. However, a cross can be made which will produce nearly all pistillate or staminate individuals. If the proper pistillate hermaphrodite plant is selected as the pollen-parent and a pure pistillate plant is selected as the seed-parent it is possible to produce an F1, and subsequent generations, of nearly all pistillate offspring. The proper pistillate hermaphrodite pollen-parent is one which has grown as a pure pistillate plant and at the end of the sea son, or under artificial environmental stress, begins to develop a very few staminate flowers. If pollen from these few staminate flowers forming on a pistillate plant is applied to a pure pistillate seed parent, the resulting F1 generation should be almost all pistillate with only a few pistillate hermaphrodites. This will also be the case if the selected pistillate hermaphrodite pollen source is selfed and bears its own seeds. Remember that a selfed hermaphrodite gives rise to more hermaphrodites, but a selfed pistillate plant that has given rise to a limited number of staminate flowers in response to environmental stresses should give rise to nearly all pistillate offspring. The F1 offspring may have a slight tendency to produce a few staminate flowers under further environmental stress and these are used to produce F2 seed. A monoecious strain produces 95+% plants with many pistillate and staminate flowers, but a dioecious strain produces 95+% pure pistillate or staminate plants. A plant from a dioecious strain with a few inter sexual flowers is a pistillate or staminate hermaphrodite. Therefore, the difference between monoecism and her maphrodism is one of degree, determined by genetics and environment.

Crosses may also be performed to produce nearly all staminate offspring. This is accomplished by crossing a pure staminate plant with a staminate plant that has produced a few pistillate flowers due to environmental stress, or selfing the latter plant. It is readily apparent that in the wild this is not a likely possibility. Very few staminate plants live long enough to produce pistillate flowers, and when this does happen the number of seeds produced is limited to the few pistillate flowers that occur. In the case of a pistillate hermaphrodite, it may produce only a few staminate flowers, but each of these may produce thou sands of pollen grains, any one of which may fertilize one of the plentiful pistillate flowers, producing a seed. This is another reason that natural Cannabis populations tend toward predominantly pistillate and pistillate hermaphrodite plants. Artificial hermaphrodites can be produced by hormone sprays, mutilation, and altered light cycles. These should prove most useful for fixing traits and sexual type. Drug strains are selected for strong dioecious tendencies. Some breeders select strains with a sex ratio more nearly approaching one than a strain with a high pistillate sex ratio. They believe this reduces the chances of pistillate plants turning hermaphrodite later in the season.


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## ENGLAND123 (Nov 12, 2010)

Some info on genetics i thought might help you people


gotta love white widow :d


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## greenavenger (May 1, 2011)

thanks alot england123 very informative an well written.


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