Breeding Guide part (1) -Breeding
 
Mellow Gold - Breeding Guide part (1)
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:

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    * 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.

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    * 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.

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    * 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.

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    * 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.

Breeding Guide Part (1b) - Breeder Goals

    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.

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    * Luther Burbank (in James, 1964)

    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 strain, 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 (1978) 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 of Cannabis Strains