4.6 ~ Polyploidy
Cannabis usually is a simple diploid plant, but polyploids having several sets of chromosomes can be produced by mutation. Polyploid cannabis usually is larger, produces more resin, and reproduces better than diploids. It is distinguishable by its darker, thicker foliage, and by microscopic analysis. Tetraploid monoecious hemp plants are selected by examination of the number and size of stomata, the number of epidermis and stoma cells, the size of pollen grains, and their number of pores. (19)
Polyploids are valuable for their genetic diversity, but they are unpredictable and usually are unstable in the first generation. They also tend to be sterile and must be propagated by clonal cuttings to be useful for subsequent breeding.
Studies by Warmke and Zhatov revealed that the normal sex ratio for diploids (2n) is nearly 1:1, but tetraploids (4n) form a new class (XXXY) and develop about 7.5 females:1 male, plus female-hermaphrodites. The XXXX is female; XXXY is female-hermaphroditic; XYYY is male-hermaphroditic, and YYYY is male. The XY determination of sex does not account, however, for the development of some monoecious strains. Seemingly, the sexual expression of hemp can be controlled by some other gene set(s) influencing different aspects of flowering. Environmental conditions also can overpower the genetic expression of Cannabis' gender, especially in the final stages of flower production. (20-23)
A. Zhatov (1979) reported these results of his research into hemp genetics:
"Change of ploidy... induced changes on some economically valuable characteristics and biological features. Tetraploid plants of dioecious hemp are characterized with sharply pronounced dioecism: plants with sexual deviations appear in the population of tetraploid hemp. Sex chromosomes of hemp on the tetraploid level play a paramount part in sex determination, but the process of determination is affected by autosomic genes...
"The viability of microspores of polyploid hemp is lower as compared with microspores of diploid hemp. During the storage, polyploid pollen loses the ability to produce pollen tubes of normal length. Selection of plants with the best regulated meiosis may raise the viability of polyploid microspores." (24, 25)
A. Zhatov, N. Migal, and other researchers have used gamma-irradiation of hempseed to mutate the subsequent plant. Presowing irradiation causes a drastic decrease in the survival rate of dioecious male plants and monoecious heterozygotic plants. Male sterility is manifested by empty pollen grains. The proportion of male plants in M1 is reduced to about 14%, and the height of plants is reduced by almost 75%. The number of branches and seed yields are increased, and the fiber content is increased by 30%. (26)
W. Hoffman and E. Knapp treated hemp seeds with x-rays, with these results:
"With increased dosage, the damage to the plants increased, the number of survivors decreased, and the sex ratio changed in favor of the females... With increased dosage, an increasing number of divergent types arose, especially of monoecious plants, and of male-like females. With increased dosage of x-rays, an increased percentage of tendrilled plants was also found... It is possible by means of x-ray treatment to change the sexuality of hemp and to get the normal dioecious hemp to a constant monoecious strain."
When hemp pollen is treated with ultraviolet light for one hour, the seed obtained from the resulting plants produces twice as many females as males.
Colchicine--- Tetraploidy can be induced by the mutagenic alkaloid colchicine, which is found in the autumn crocus, (colchicum autumnale). Colchicine allows a cell to double its chromosomes, but prevents meiosis (the splitting of cells), thus forcing the cells to become polyploid. When applied to cannabis, colchicine produces tetraploid plants which tend to be taller, with greater stem diameter, seed and pollen size. The THC content can increase up to 250%.(27)
A. Zhatov, et al., reported these findings from their research:
"The greatest % of polyploid plants is obtained when hemp plants are treated with 0.5% colchicine solution for 2 hours in the phase of cotyledon leaves. The treatment with colchicine solution inhibits growth. This inhibition continues for 2.5-3 weeks, after which the surviving plants resume normal growth and development. The guard cells in the leaves and the pollen grains of tetraploid plants are larger and the number of pores on the pollen grains are greater. Tetraploid plants are taller and the diameter of their stems, seed size and weight of 1000 seeds are greater. The anatomical structure of the stems differs from the diploid plants in a greater amount of primary and secondary fiber. The pollen viability of the tetraploid plants is lower than that of diploid plants. Vegetation period in tetraploids continues 8-15 days longer than in control plants." (28)
Colchicine also can sprayed on the seeds while they are developing on the mother plant. The flowers of plants treated in this manner should not be smoked because the concentration of colchicine may be dangerously high. A third method is to soak seeds in the solution for 2 to 4 hours. Colchicine stimulates the development of the taproot at first, but this effect ceases within a week; then the seedlings go into shock. About 30% of the survivors will be polyploid.
Colchicine can be bought, or prepared by grinding 100 grams of colchicum seeds to powder and percolating with 2 volumes of ethanol and 1 volume of water. The solution contains approximately 4 milligrams of colchicine. Label the bottle and store it safely: colchicine is toxic. Always wear rubber gloves when handling colchicine.
