Authors: Jai Prakash A. K. Goswami and K. Singh
Division of Fruits and Horticultural Technology
Indian Agricultural Research Institute, New Delhi-12
Email: Singhjai2001@rediffmail.com
Papaya (Carrica papaya L.) is a native of Tropical America and belongs to family Caricaceae. It is diploid (2n=2x=18) with basic chromosome number (x=n=9) Earlier 31 species of Carica were reported but recently another taxonomic revision was proposed and supported by molecular evidence that genetic distance were found between papaya and other related species. Some species that were formerly assigned to Carrica were classified as Vasconcella (Badillo 2002).
The papaya usually flowers 3-6 months after transplanting and identification of the desirable plants at seedling stage would help in raising the orchard with appropriate design. In sub-tropical areas, dioecious varieties such as Pusa Nanha and Pusa Dwarf are preferred, because of their dwarf stature high and yields. Conversely in the tropical areas, gynodiocious varieties are preferred because of their high yield potential. In both cases, being unable to identify the sex type of the seedlings prior to planting is a limiting factor. Sex expression in papaya is controlled by a single gene with three alleles, which have a pleiotropic effect.
Floral Biology:
Papaya is a polygamous plant three basic types of flowers viz. staminate, pistillate and hermaphrodite (bisexual). Of these, only pistillate is stable, whereas flowers of hermaphrodite and male vary in sex expression under different environmental conditions.
Staminate flowers :
Staminate flowers serve as pollinators. These plants show 1 to 1.5 m long flower stalks hanging out from trunk. The individual flower is small, tubular and contains stamens only.
Pistillate Flowers
Pistillate flowers are large, yellow, borne singly or in - group of three in the leaf axils close to the trunk. The flowers have fine large twisted and fleshy petals that surround an ovary, which swells and develops into papaya fruit. The fruits developed from pistillate flower are spherical to oblong shaped having thick, yellow to orange coloured flesh in different cultivars with large to small cavity in which numerous round wrinkled black seeds are attached.
Hermaphrodite or bisexual flowers
It has both male and female organs. Individual flowers are 3.5 to 4.5 cm long with tubular base that widens into goblet shape and then spreads out into 5 thick yellow coloured recurred petals. In between these petals, male organs i.e. stamens are present and female organs containing oblong ovary which develops into cylindrical fruits.
• The dehiscence of anther takes place 24 hours before anthesis in all the species of Carrica, the dehiscence in staminate and hermaphrodite flowers takes place between 10 to 12 hours before anthesis.
• High temperature and low humidity hastens the time of anther dehiscence.
• In papaya, high percent pollen germination can be achieved with 5 percent sucrose solution. Papaya pollen can be stored up to 5 years without loosing the viability if proper conditions are created for storing. The floral diagram is presented below:
• Stigma become receptive one day prior to anthesis and it remains receptive two days after flower anthesis.
• The best hour of the crossing is between 8-10 hours in the forenoon during sunny days.
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Pollination
If a papaya plant is inadequately pollinated, it will bear a light crop of fruits lacking uniformity in size and shape. Therefore, hand-pollination is advisable in commercial plantations that are not entirely bisexual. Sometime, seedless fruit may observe in the areas where gynodioecious varieties / hybrids are dominating in the cultivation. These seedless fruits are due to lack of proper pollination and fertilization.
About Author / Additional Info:
I am working as a senior scientist at IARI New Delhi.