2013 Annual Report
From late 2011 onwards with fruit available from the Poamoho Research Station and from a local grower, we have continued research on the use of microbial antagonists to reduce the incidence of postharvest diseases of papaya, especially anthracnose. The objective was to enhance the effectiveness of the response by coupling our selected yeast (#581) with various fruit coatings reported to reduce postharvest diseases in other fruit such as apples. In previous studies, we had noted that the yeast was most effective in controlling Anthracnose when applied days after fungi inoculation. In the current year, Gum Arabic was applied after fungus inoculation, with and without yeast #581. A coating of 2% Gum Arabic alone showed a similar inhibitory effect on Anthracnose development as yeast #581, when applied on inoculated papaya five days later in storage. Coating papaya with Gum Arabic containing yeast culture reduced disease incidence and severity to a quarter of that in the controls. A 2% weight to volume (w/v) concentration was most effective. Using the on-line resource BLAST2GO, we have generated functional annotations of all the predicted papaya genes for which there are predicted functions. This annotation includes Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway maps, InterPro and Enzyme Codes. This database will enable us to analyze the gene expression data during fruit ripening that we are now generating. We have focused throughout this reporting period on characterizing the ripening characteristic of the lines selected out of the QTL softening segregation study. In addition, crosses have been made between the slow-ripening line and the virus resistant line “SunUp” to develop a homozygous virus resistant slow ripening line. All the F-1 generated from “SunUp” as the female pollinated with 4-16 pollen were Gus positive though fruit firmness was similar to “SunUp”. However, when “4-16” was the female parent only 50% of the F-1 papaya contained virus resistance genes (Gus positive) and the fruit showed ripening pattern and firmness similar to “4-16." Selections have been made in these cross after confirming that did contain the transgene for virus resistance. Trees with low summer sterility and slow ripening characteristic have been used as a screening criterion. If our approach is successful, the timing and degree of fruit softening can be more closely controlled to suit market needs. Controlling ripening will extend shelf life and improve market ability and enlarge the geographic area of distribution.