Cannabis Sativa L: Sex differentiation

Cannabis Sativa L: Sex differentiation

This part of the research is dedicated to scientific data on cannabis sex differentiation.

Sex determination

Cannabis Sativa L are dioecious species, which mean that there are male and female plants. Only 7% of all known to us plants are dioeious and sex is determined by X and Y chromosomes. However, some cannabis plants could be monoecious (or hermaphrodite). [1,2]

cannabis-sexes
Dioecious cannabis plants develop in separate male and female plants

Male and female plants can be identified via microscopic method as soon as the leaves of the fourth node emerge. [3]

Human genome illustrates differences between autosomes and sex chromosomes.
Human genome illustrates differences between autosomes and sex chromosomes.

Cannabis Sativa L genome is composed of 9 pairs of autosomes (not sexual chromosome) and 1 pair sexual chromosomes (X and Y). But X and Y chromosomes are not the only components responsible for sex determination. The research shows that sex is determined by the ratio of X chromosome and autosomes rather than an active Y chromosome. This means that presence of Y chromosome does not constitute male plant. [3]

Origin and theory for sex determination of hermaphrodite cannabis plants

Monoecious cannabis plant (hermaphrodite) express both male and female flowers
Monoecious cannabis plant (hermaphrodite) express both male and female flowers

Monoercious (or hermaphrodite) varieties were observed as well and it was identified that this is a recessive trait. Hemp producers prefer hermaphrodite plants because of higher seed yield, higher crop homogeneity and easier harvest. However, sexual phenotype of monoercious plants is not stable. Maintaining hermaphrodite plants require strict selection otherwise they will reverse back to male and female plants. Sex determination of hemp is also affected by external factors such as hormonal treatments, photoperiod or nitrogen status. The sex determination of monoercious plants is not clear. According to one theory there are XX, XY and YY forms and hermaphrodite plants have XX. Other studies claim that there is no specific chromosome type and they suggest that hermaphrodite plants are result of single gene mutation. [3]

First autoflowering cannabis breeders

Russian scientists, Grishko and Malusha (1935) and Grishko et al. (1937) were the first to breed monoecious (hermaphrodite) and autoflowering dioecious hemp varieties back in the 30s. Grishko discovered that dioecious plants could be bred to hermaphrodite varieties and using inbreeding they can create new varieties. [6]

Sex reversion in cannabis

Cannabis Sativa L allows total or partial reversion of the sex. For example, female plants can be reversed to male plants by using chemicals like aminoetoxyvinlglycine, silver thiosulphate and silver nitrate, which inhibit ethylene biosynthesis. Male plants can be reversed to female by using ethephon, activator of ethylene biosynthesis. [1]

Cannabis cloning

It is known that Cannabis Sativa L could be maintained by using clones. However, prolonged usage of clones could lead to genetic mutations also known as somaclonal variations (chromosomal rearrangements). Some of these somaclonal variations could be easily revered back unless they are specifically selected to be preserved. In order to avoid somaclonal variations the plants should be monitored closely. Axillary bud proliferation is considered the most suitable and used method for plant micropropagation. [2, 5]

There are different cannabis cloning techniques and they follow strict protocols
There are different cannabis cloning techniques and they follow strict protocols

Unfortunately sex determination in Cannabis Sativa L is not simple. Although sex determination is genetic, there are also environmental factors that could influence sex determination. [4]

Sources

1. The sexual differentiation of Cannabis sativa L.: A morphological and molecular study

2. Biotechnology for Medicinal Plants: Micropropagation and Improvement

3. Sex chromosomes and quantitative sex expression in monoecious hemp (Cannabis sativa L.)

4. Some aspects of sex determinism in hemp

5. Axillary Bud Proliferation Approach for Plant Biodiversity Conservation and Restoration

6. Current status and future scenarios of hemp breeding

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