1979 ). In a female line of cucumber, silver nitrate application (0.02–0.03%)
increased the frequency of maleflowers and hermaphroditeflowers while in a
monoecious line, there was no effect (Stankovic and Prodanovic 2002 ).
The hermaphrodite condition may be artificially induced in marihuana when a
grower or seed producer wishes to produce seeds that are“feminized”. These seeds
are those which are produced on a genetically female plant with hermaphrodite
flowers, akin to self-pollination, resulting in a much higher chance of producing
female plants (95%) than seeds resulting from cross-pollination (which would
produce an approximately 1:1 ratio of male: female plants). The strategy of femi-
nization can save production time and space and reduce costs since only female
plants are used in marihuana production and the required screening out of male
plants is avoided. On some occasions, however,“feminized”seeds can still give
rise to male plants (5–10% frequency), an outcome that requires further study.
Feminized seeds are more expensive to produce, and can inadvertently cause more
hermaphrodites to develop in the subsequent generation. It has been suggested that
female seed development can be encouraged by treatingflowers resulting from a
cross between male and female plants (which should produce a 1:1 ratio of male:
female) by using silver thiosulfate or hormone applications (UNODC 2009 )
although this has not been verified.
19.5 Genetics of Cannabis
The genetic background of present-day marijuana strains likely originated from
plants grown in remote areas of Afghanistan, Columbia, Mexico, India, and
Pakistan. The species has a diploid genome (2n = 20) with a karyotype composed
of nine autosomes and a pair of sex chromosomes (X and Y) (Sakamoto et al.
1998 ). Female plants, which are cultivated and sold as marijuana, are homogametic
(XX) and males are heterogametic (XY), with sex determination controlled by an
X-to-autosome balance system (Ming et al. 2011 ). The estimated size of the haploid
genome is 818 Mb for female plants and 843 Mb for male plants, owing to the
larger size of the Y chromosome (Sakamoto et al. 1998 ). Recent studies by Sawler
et al. ( 2015 ) and Lynch et al. ( 2017 ) demonstrated that a high level of intraspecific
genetic variation is present inC. sativa. Sequencing of the cannabis genome in
2011 using strain‘Purple Kush’revealed a transcriptome of around 30,000 genes,
and a high level of sequence (single nucleotide) variation was observed among four
lines, including hemp (Van Bakel et al. 2011 ). Hemp was proposed to be more
genetically similar toC. indicathanC. sativa(Sawler et al. 2015 ; Lynch et al.
2017 ) and can be distinguished from marihuana using molecular approaches.
Currently, marijuana production does not utilize highly-bred cultivars such as
those found in most food crops. Instead, genetic strains are developed through
crosses made from different parental backgrounds and the resulting strains are
19 Assessing Genetic Diversity inCannabis sativa... 401