Hermaphroditism in Marijuana (Cannabis sativa L.) Inflorescences – Impact on Floral Morphology, Seed Formation, Progeny Sex Ratios, and Genetic Variation

Abstract

Cannabis sativa L. (hemp, marijuana) produces male and female inflorescences on different plants (dioecious) and therefore the plants are obligatory out-crossers. In commercial production, marijuana plants are all genetically female; male plants are destroyed as seed formation reduces flower quality. Spontaneously occurring hermaphroditic inflorescences, in which pistillate flowers are accompanied by formation of anthers, leads to undesired seed formation; the mechanism for this is poorly understood. We studied hermaphroditism in several marijuana strains with three objectives: (i) to compare the morphological features of this unique phenotype with normal male flowers; (ii) to assess pollen and seed viability from hermaphroditic flowers; and (iii) to assess the effect of hermaphroditism on progeny male:female (sex) ratios and on genetic variation using molecular methods. The morphological features of anthers, pollen production and germination in hermaphroditic flowers and in staminate inflorescences on male plants were compared using light and scanning electron microscopy. Seeds produced on hermaphroditic plants and seeds derived from cross-fertilization were germinated and seedlings were compared for gender ratios using a PCR-based assay as well as for the extent of genetic variation using six ISSR primers. Nei's index of gene diversity and Shannon's Information index were compared for these two populations. The morphology of anthers and pollen formation in hermaphroditic inflorescences was similar to that in staminate flowers. Seedlings from hermaphroditic seeds, and anther tissues, showed a female genetic composition while seedlings derived from cross-fertilized seeds showed a 1:1 male:female sex expression ratio. Uniquely, hermaphroditic inflorescences produced seeds which gave rise only to genetically female plants. In PCR assays, a 540 bp size fragment was present in male and female plants, while a 390 bp band was uniquely associated with male plants. Sequence analysis of these fragments revealed the presence of Copia-like retrotransposons within the C. sativa genome which may be associated with the expression of male or female phenotype. In ISSR analysis, the percentage of polymorphic loci ranged from 44 to 72% in hermaphroditic and cross-fertilized

Cannabis Inflorescence Yield and Cannabinoid Concentration Are Not Improved with Long-Term Exposure to Short-Wavelength Ultraviolet-B Radiation

“…UV radiation accelerated plant senescence (i.e., deterioration with age) symptoms in both inflorescence and foliar tissues. Female inflorescence maturation can normally be characterized by carpel swelling and the transition of stigmas from white to brown in the final days before harvest (Punja and Holmes, 2020). Although the number of days between the initiation of the 12-h photoperiod and appearance of inflorescences was unaffected by UV exposure (data not shown), plants exposed to higher UV-PFDs exhibited earlier stigma browning without carpel swelling (Figure 4).…”

Photons from NIR LEDs can delay flowering in short-day soybean and Cannabis: Implications for phytochrome activity

“…Botanically, these terms are distinct: monoecious refers to the presence of separate male and female flowers on the same plant, while hermaphrodite refers to the presence of both male and female reproductive organs within an individual flower [47]. In practice, the distinction is not important because both monoecious and hermaphroditic Cannabis produce pollen and potentially reduce product quality and value [48]. The tendency of Cannabis to form monoecious or hermaphroditic plants is under genetic and environmental influence [49,50].…”

Untargeted Metabolomic Analyses Reveal Chemical Complexity of Dioecious

“…[15] Being mainly dioecious, Cannabis segregates into distinct female and male plants, although monecious phenotypes with bisexual flowers or inflorescences bearing separate male and female flowers occur to a lesser extent. [15,16] Reproductive commitment occurs as early as the emergence of the fourth leaflet pair. [15] Sex expression can be influenced by temperature 1).…”

“…Male and hermaphroditic plants have less floral biomass, reduced phytocannabinoid yield, and also negatively impact female inflorescence quality via fertilisation and initiation of seed development. [16] Prolonged virginity in female plants during flowering also aids in the formation of congested pistillate inflorescences which improves phytocannabinoid yield. [16,23] Conversely, monoecy can be desirable for the cultivation of industrial hemp.…”

“…[16] Prolonged virginity in female plants during flowering also aids in the formation of congested pistillate inflorescences which improves phytocannabinoid yield. [16,23] Conversely, monoecy can be desirable for the cultivation of industrial hemp. Not only does this reduce crop heterogeneity, but also mitigates early flowering and senescence of unisexual male plants which can complicate mechanical harvesting of both stems and seed.…”