Chemical Masculinization of Female Cannabis sativa L.: Impacts on Pollen Viability and Feminized Seed Production

Cannabis is usually dioecious, with male and female flowers on separate plants. Cultivators prioritize the use of female plants because their flowers contain a higher density of glandular trichomes, the primary source of cannabinoids, compared to male flowers. Feminized seeds, which give rise exclusively to female plants, are highly valued in the cannabis industry. These seeds are produced by crossing a natural female plant with another female plant that has been masculinized to generate pollen. Masculinization is achieved by inhibiting ethylene and/or applying gibberellins prior to flower initiation in female plants. Currently, silver thiosulfate (STS) is the most common treatment used in the cannabis industry, though environmental concerns arise from silver applications. This study compared STS with three other ethylene-inhibiting agents: aminoethoxyvinylglycine (AVG), cobalt nitrate (CBN), and 1-methylcyclopropene (1-MCP). Some STS and CBN treatments also included gibberellic acid as a synergist. STS-treated plants displayed the most effective masculinization and pollen dispersal, compared to plants treated with AVG. Only STS and AVG generated sufficient pollen for collection. This pollen was initially tested for germination potential and subsequently stored for up to five weeks at 22.2 °C, 7.2 °C, or 1.1 °C.Germination rates ranged from 2.2% to 5.8%, underscoring the influence of storage conditions and highlighting the need to refine preservation methods to enhance agricultural viability. Pollen from plants treated with AVG remained viable for three weeks at 1.1 °C, although there were concerns about a high risk of phytotoxicity. STS-treated pollen also remained viable for three weeks at the same temperature. Neither CBN nor 1-MCP treatments were effective in inducing masculinization. No clear synergistic effect of gibberellic acid combined with STS or AVG was observed; however, growth stunting led to increased mortality. Due to pollen viability and phytotoxicity problems with AVG, STS remains the best treatment to masculinize female cannabis plants when breeding for feminized seeds.