Comparative reproductive biology and fitness tradeoffs across reproductive phenotypes in dioecious and gynodioecious papaya

Papaya (Carica papaya L.) exhibits a polymorphic sexual system encompassing both dioecious and gynodioecious cultivars, yet the quantitative reproductive fitness consequences of its multiple sex forms remain insufficiently characterised. The present investigation provides a comprehensive evaluation of pre- and post-fertilisation reproductive traits across six floral phenotypes such as staminate, pistillate, reduced elongata, elongata, pentandria, and carpelloid pentandria, in four commercially important cultivars representing dioecious ('Ranchi Local' and 'TNAU Papaya CO-8') and gynodioecious ('F₁ Red Lady' and 'Arka Prabhat') breeding systems. Pollen production per anther, viability, in vitro germination, pollen size, time of anthesis, anther dehiscence, and stigmatic receptivity duration were quantified, along with post-fertilisation parameters including ovule maturation period, ovule degeneration percentage, fruit-set duration, and viable seed-set. Staminate flowers produced the highest pollen output (11,396-11,802 grains per anther) with superior viability (71-75%) and germination (63-68%), whereas reproductive fitness declined progressively across hermaphroditic forms in the order RE > EL > PA > CP. Carpelloid pentandria flowers exhibited 39-45% lower pollen output, 66-68% reduced viability, the highest ovule degeneration (24-26%), and the lowest viable seed-set (46-51%). Pistillate flowers maintained extended stigmatic receptivity (66-73 h), minimal ovule degeneration (16-18%), and the highest seed-set (59-69%). Correlation analysis revealed strong positive associations among pollen attributes and seed production, while ovule degeneration and delayed reproductive timing were negatively associated with reproductive success. The findings establish a clear reproductive fitness gradient among papaya sex forms and provide quantitative reference data for breeding, cultivar selection, and clarifying the evolutionary implications of sexual-system diversity in papaya.