Microbial Biocontrol of Postharvest Papaya Diseases

Papaya fruit postharvest losses of up to 75% have been reported to Hawaii shippers by mainland USA wholesalers and retailers. These losses are associated with postharvest disease, often associated with storing color-break fruit for more than three weeks at temperatures of 10^oC or lower temperatures and mechanical injury. Postharvest disease has been controlled by hot water dips, hot water spray treatments and fungicides. Microorganisms were isolated from papaya fruit surface and evaluated for their ability to control postharvest disease by their actions as antagonistic microorganisms to the disease carrying microorganisms. Postharvest disease incidence varied with season. A greater incidence of anthracnose occurred during cool season while stem end rot was more prevalent in the warm season. Anthracnose usually developed after one week at (22^oC) and stem end rot developed at a slower rate after 10 days. Three yeast isolates that had biological activity against anthracnose were tested in vivo on papaya fruit. Half the treated and inoculated fruit were stored at 10^oC for 10 days before ripening at ambient temperature. In addition to the three yeast isolates, 0.5% thyme oil, 1.5% medium molecular weight chitosan and wax were also tested. Application time of the yeast isolates influenced the effectiveness their antagonist activity. All three yeast isolates tested, #581, #961 and #1061 showed antagonistic activity against anthracnose when applied one day after pathogen inoculation in papaya ripened at ambient temperature. However, when the papaya were stored at 10^oC before ripening, only yeast isolate #1061 was effective in reducing the anthracnose development.