Breeding of Fruit and Plantation Crops

Botany

• Papaya belongs to family Caricaceae and genus Carica having about 40 species. It is a dioecious plant but gynodioecious cultivars are also available. The stem is hollow and soft wooded. It is usually unbranched when young but at later stage upright shoots develop at its terminal growth due to obstruction. The leaves are palm like with long stalks. Flowers are cymose, fragrant borne in leaf axils. The fruit is a fleshy berry. The fruits from pistillate flowers are ovoid-oblong to nearly spherical in shape and the fruits from hermaphrodite flowers are pyriform, cylindrical or grooved.

Floral biology and pollination

• Dioecious papaya produces male and female trees separately on different plants in the ratio of 1:1, while gynodioecious cultivars produces both female and andromonoecious trees in the ratio of 1:2. Female and male flowers develop within 32 and 42 days respectively after bud initiation. The period from bud initiation to anthesis is shorter for male than female flower bud (Dhaliwal et al., 1991). Stamen development occurred prior to ovary development in the hermaphrodite flower and stamen differentiation was observed 56-59 days before anthesis.


• Anther dehiscence starts 18-36 hours before the flowers opening and continues depending upon the weather conditions and stigma becomes receptive a day before the flower opening and remaining receptive for 6 days. The peak anthesis was observed between 5.00-6.00 a.m. The receptivity of stigma was found maximum on the day of anthesis in most of the species (Subramanyam and Iyer, 1986).
  


• To ensure good fruit set in the dioecious cultivars of papaya (e.g. CO1, CO2, CO4, CO5, CO 6, Pusa Giant, Pusa Dwarf, Pusa Nanha,), the female and male ratio should be 20:1. However, maximum number of andromonoecious trees are retained in gynodioecious varieties (eg. CO3, CO7, Coorg Honey Dew, Sun Rise Solo, Sun Set Solo etc.) Further, insects are the major pollinating agents in papaya.

Sex forms
There are two major sex forms in papaya

• Dioecious: male and female trees segregate in the ratio of 1:0.sibmating is done for maintaining of purity.
• Gynodioecious: Female and andromonoecious (female + bisexual flowers in a single tree) trees segregated in the ratio of 1:2. Selfing of bisexual flowers is done for obtained pure seeds