Sex expression in papaya: morphological marker, molecular genetics and environments

Papaya belongs to the family Caricaceae and is a polygamous species. Papaya plants are extremely diverse in their sexual systems. Three sex types are available in papaya viz., male, female and hermaphrodite and are controlled by a single gene with three alleles (m, M1, M2). The genotypes represent gynoecious, androecious and hermaphrodite individuals. The extremes of humidity reduce the storage life of papaya pollen but under ideal (artificial) storage conditions it potentially remains viable for about 5-6 years. Ninety percent of freshly dispersed pollen grains were viable in summer but viability dropped to about 45% in some lines and as low as 4.5% in others in winter. The stigma attained receptive two days before anthesis and continued up to five days after anthesis but began to decline gradually upto five days after anthesis. Papaya plants produce fruit either through cross-pollination or self-pollination or parthenocarpy depending on their sex types. On an average 1,000 seeds are found in a single fruit, indicating that 1,000 viable pollen grains may fertilized receptive stigma. Identification of desirable plant population at early stage is very important and crucial for papaya cultivation. Several morphological characters such as seed coat colour, root morphology etc. found to be related with the sex types in papaya. Seed coat color, petiole thickness, stems color worked as a morphological marker for sex determination in Papaya. The black and dark brown seed coat color exhibited higher frequency of the female and hermaphrodite plants. On the other hand, higher petiole thickness and light green act as an indicator female plant at flowering stage and unique purple stem color was reported to express as hermaphrodite plants.