SCREENING CARICA-PAPAYA X CARICA-CAULIFLORA HYBRIDS FOR RESISTANCE TOPAPAYA RINGSPOT VIRUS TYPE-P

Carica papaya, C. cauliflora and interspecific hybrids of these specie s were screened for resistance to two Australian isolates (338, 445) o f papaya ringspot virus-type P (PRSV-P). Plants were manually inoculat ed with PRSV-P in the glasshouse and the reaction assessed 30 days lat er by back-inoculation to susceptible Cucurbita pepo and by a plate-tr apped antigen-enzyme linked immunosorbent assay (PTA-ELISA). Both pare nts and interspecific hybrids were also planted adjacent to infected C . papaya and 30 days later tested for PRSV-P by PTA-ELISA. All intersp ecific hybrid and C. cauliflora plants manually inoculated in the glas shouse or planted in the field failed to become infected, whereas C. p apaya plants, in both situations, were infected by PRSV-P. In addition , the surviving interspecific hybrid and C. cauliflora plants tested n egative, while all C. papaya plants were positive for PRSV-P in both t he back-inoculation and PTA-ELISA tests. Thus, the interspecific hybri d and C. cauliflora plants were resistant to the Australian PRSV-P iso lates.