Postharvest Physiology of Fresh Hawaiian Commodities

Non-Technical Summary: The marketing of high quality fresh Hawaii fruits, vegetables, and ornamentals requires that the commodity be grown for optimum quality, and harvested and handled post-harvest to maintain that quality. Postharvest physiology and handling research plays a critical role in assuring the maintenance of commodity quality. Postharvest quality is in large measure set before harvest, hence preharvest conditions need to be considered in evaluation of quality and its maintenance. The smaller quantities of tropical commodities produced, the distances to market, the commodities inability to be stored at low temperatures and the presence of fruit flies and other insects requiring postharvest treatments compound the research needed to ensure quality products are marketed. In this project, we will continue collaboration with industry groups to directly address their needs for postharvest applied research and carry out long-term basic studies using molecular techniques to develop new strategies to address postharvest problems for Hawaii's horticultural crops. Research will continue on pineapple looking for solutions to the precocious flowering and cultural practices to modify acidity levels. Papaya research will focus on looking for non-pesticide disease control and the modification of fruit ripening to increase storage life. Irradiation and ethylene interact during papaya fruit ripening and this interaction will be another research effort to reduce its impact. Research on other tropical fruits and vegetables has been short term in nature to address immediate concern especially in providing up to date information in handling these commodities. Ornamental research will continue to look for approaches to maintain product quality and thereby extend vase life and reduce postharvest losses. The potential for Jatropha as a biofuels will remain synchronization of field flowering and selection of material will non-toxic seed cake.<P> Approach: A. Pineapple Objective 1 -Flowering: Weekly treatments of ReTain (AVG) at 100 ppm will be applied as 125 or 250 gallons per acre in early December to reduce the percentage of flower development (budding and thus sharpened the harvest peak. We have generated 18 independent transgenic pineapple plant lines with an ACS antisense construct. Plants of the individual transformed lines and the control will be grown in a randomized plot design in pots at the University of Hawaii Whitmore Sub-Station. Plants will be monitored fortnightly for six months from early December through May. At first indication of flowering (red bud stage), the plant will be scored as having flowered. If flowering has not occurred by May, the plants that have not flowered will be induced to flower with Ethephon. The Ethephon solution (100 ppm) will be poured into the heart of the plant with about 25 mL per plant. Pineapple Objective 2. - Low Acid Fruit - Fruit are to be randomly selected from field trials having different management strategies fertilization and irrigation, and returned to the laboratory within 4 hours of harvest. Twenty five fruit are to be evaluated with in 24 hours of harvest and the remaining twenty fruit stored for 14 days at 7oC, then 7 days at 22oC, before evaluation. Papaya Objective 1 The ripening variant, Line #8 softens to the edible stage in 6 days versus 11 days for the commercial varieties. At the other extreme, Line #4-16 does not begin to soften until 14 days from mature green stage and reaches the edible soft stage at 21 days. We have found a single QTL for this slow ripening trait and are now using papaya microarrays that we developed to determine the expression of the possible transcription factors present in this QTL region. The microarray analysis will be confirmed with RT-qPCR. Papaya Objective 2 - Determine the regulation of cell wall degrading enzymes in ripening related fruit softening. The objective of this section of our project is to complete the evaluation of the molecular biology and physiology of 8 PCR-positive putative antisense endoxylanase lines and 32 other possible antisense lines that may have delayed softening. The full-length endoxylanase clone (CpaEXY1) was inserted behind the CaMV-35S or ubitiquin promoters and in front of a NOS 3' terminator sequence so that the xylanase was in the antisense direction. DNA insertion (determined by Southern analysis), RNA expression, endoxylanase activity, and protein content (determined by using endoxylanase antibodies) will be assayed to characterize the putative transformed lines. Fruit ripening will be evaluated by measuring respiration rate, ethylene production, and firmness.