How STS turns female cannabis plants into pollen donors

The induction of staminate flowers in genetically female Cannabis sativa is widely used for feminized seed production, yet its anatomical and ontogenetic basis remains poorly understood. This study examined silver thiosulfate (STS)-induced masculinization in genetically female plants of C. sativa cv. 'Pasionaria S' using stereomicroscopy, light microscopy, confocal laser scanning microscopy, pollen viability assays, and open-pollination tests. STS redirected floral sexual identity within the conserved architecture of the female reproductive shoot. Staminate floral meristems were first detected at 7 days post-treatment, while previously initiated pistillate flowers persisted; by 21 days, the reproductive apex was dominated by staminate structures. Induced male flowers corresponded to type II unisexual flowers, with early staminal primordia and no evidence of gynoecial primordia. Three trajectories were identified: fertile male flowers with normal anther development and viable pollen, sterile flowers with collapsed anthers and disrupted microsporogenesis, and occasional mixed flowers with localized androecial expression. Pollen viability reached 54%, and open pollination confirmed seed formation. These results show that STS-induced masculinization is a staged and heterogeneous redirection of floral meristem identity.