DEVELOPMENT OF CARICA INTERSPECIFIC HYBRIDS

Abstract

Papaw production in Australia is limited by five major diseases: papaw dieback and yellow crinkle (caused by mycoplasmas); Phytophthora fruit, stem and root rots; black spot (Asperisporium caricae); and papaya ringspot virus-type P (PRSV-P). PRSV-P is the greatest problem for papaya production worldwide and potentially poses the greatest disease threat to the Australian industry. Procedures have been developed to hybridise papaya with related Carica species that are PRSV-P resistant (C. cauliflora, C. quercifolia, and C. pubescens). These procedures may also allow access to other characteristics of wild species eg. Phytophthora resistance (C. goudotiana), high sugar content (C. quercifolia) and cold tolerance (C. pubescens). A highly efficient protocol was developed to rescue and germinate C. papaya x C. cauliflora immature embryos (Magdalita, et ad. 1996). Germinated embryos formed embryogenic cultures on hormone free agar solidified medium and multiple hybrid plants were produced. The C. papaya x C. cauliflora hybrids lacked vigour and were generally infertile. Subsequently, the protocol has been adapted to produce hybrids between C. papaya and PRSV-P resistant species C. quercifolia and C. pubescens. Hybrid plants are growing vigorously in the field, and a few C. papaya x C. quercifolia plants have produced some viable pollen. Interspecific hybrid plants have been produced between C. papaya, and C. goudotiana and C. parviflora. C, parviflora has been hybridised with C. pubescens and C. goudotiana. Plants of all crosses are growing in the glasshouse or field.