Genetic Improvement of Papaya ( Carica papaya L.)

Arising from a relatively isolated center of origin, papaya has spread throughout all tropical and subtropical countries through human intervention. This global dispersal has coincided with continuous improvement of the cultivated plants through breeding programs often designed to improve the agronomic characters and to address biotic and abiotic stresses that affect papaya production. Papaya production is threatened by a myriad of problems including devastating pests and diseases as well as the inability for both farmers and researchers alike to differentiate among the three sex types, male, female and hermaphrodite at the seedling stage, among others. Many attempts have been made by researchers over the years to resolve the problems through conventional and biotechnological techniques. Conventional plant breeding has given rise to varieties that are resistant to diseases as well as high yielders of quality fruits. However, conventional techniques require 12–14 years to develop new papaya varieties. Besides, devastating viral diseases like papaya ringspot virus (PRSV) have proved almost impossible to control through conventional means. The innovative technologies and growing understanding to manipulate the papaya phenotype at the molecular level provide new opportunities for the improvement of papaya. Through gene transfer technology, it is possible to develop transgenic papaya with pest and disease resistance as well as improved nutritional quality. This chapter provides insight into conventional breeding of papaya, the role of tissue and protoplast culture as well as molecular techniques in papaya improvement such as genetic transformation, mutation breeding and marker assisted selection and breeding. In addition, the potential of parthenocarpy as well as polyploidy and somaclonal variation in papaya breeding are discussed.