Harnessing Sex Reversion via Chemical Intervention in Cannabis sativa L.

Cannabis sativa is a multipurpose dioecious species whose crop performance is governed by sex expression. Although sex is genetically determined by an X/Y chromosome system, plants can develop flowers of the opposite sex through sex reversion, commonly induced by manipulating endogenous hormone levels using plant growth regulators (PGRs). Here, we evaluated the effectiveness of PGRs that promote or inhibit major hormone pathways implicated in plant sex expression. Male and female clones from two accessions were treated with foliar applications of nine PGRs and four combinatory treatments to assess sex- and genotype-specific responses. Floral biomass and the proportion of each sex were recorded at harvest to assess treatment effectiveness. Ethylene emerged as the primary regulator of chemically modulated sex reversion in C. sativa, with its inhibition by silver thiosulfate inducing strong female-to-male reversion and its promotion by ethephon inducing equally strong male-to-female reversion in the inflorescences. Gibberellin promotion on its own resulted in female-to-male reversion at the axial nodes only, while its inhibition showed no reciprocal effects. The combination of silver thiosulfate and gibberellic acid resulted in the most complete female-to-male reversion, and all sex-reverted flowers were fertile. Together, the results indicated that flowers at axial nodes and at the terminal ends of inflorescences are under different hormonal control. Cytokinins, auxins, and jasmonates were found to exert minimal influence on sex reversion. All treatments exhibited pleiotropic effects, particularly gibberellic acid and paclobutrazol, which altered resource allocation, shifting biomass away from and towards floral tissue, respectively. These findings advance our understanding of the hormonal regulation of sex expression in C. sativa and identify optimized approaches for its manipulation.