Preharvest practices affecting postharvest quality and mineral composition of 'Hass' avocado fruit

Abstract

Fruit quality is largely determined before harvest. Postharvest treatments mainly seek tonmaintain this quality. A better understanding of the interaction between preharvest factorsnand postharvest fruit quality is required in order to find the best practices to optimize qualitynand reduce variability in quality. This thesis studied (1) the extent of variability in thenpostharvest performance of 'Hass' avocado fruit caused by production locality, harvest datenand fruit canopy position; (2) the underlying causes of quality variation such as mineralnnutrition; and (3) cultural practices such as irrigation, nitrogen fertilization and the use of thengrowth retardant paclobutrazol to manipulate fruit quality.Significant variation in fruit quality was noted between 6 production localities in south-eastnQueensland, where fruit were harvested at 3 stages of maturity (estimated at 24, 29 and 34%ndry matter, DM), and ripened immediately at 22oC or following 7oC storage for 3 weeks.nFruit from the warmer climates were smaller and less elongated than fruit from the coolernclimates. The days to eating soft and fruit Ca and Mg concentrations declined with laternharvests in fruit from most, but not all locations, while fruit mass and skin colour at harvestnincreased with later harvests. Anthracnose severity was either not affected by harvest stage,nor increased with later harvests in seasons with higher severity in fruit from the warmnenvironments.Long-term storage potential of fruit was influenced by production locality, harvest date andnmineral concentrations. Fruit from the sub-tropical (Childers) and semi-temperaten(Toowoomba) environments were stored at 7, 2 or 1oC for 3 or 5 weeks before ripening.nFruit stored at 7oC did not develop skin discolouration during storage, but developed fleshndisorders, especially in less mature fruit. Storage at 1 or 2oC significantly reduced thenseverity of mesocarp discolouration, but increased the severity of skin discolouration.nEarly harvested fruit from Childers had 40% of fruit skin affected by discolouration and latenharvested fruit from Toowoomba had 25% of skin discolouration. Vascular browning wasnonly found in fruit from the Toowoomba district following 7oC storage.Canopy height and depth had significant effects on finit size, shape and % DM, but not onnpostharvest finit quality in the Maleny orchard (representing cool sub-tropicalnenvironments). However, canopy aspects had effects on postharvest quality and mineralnconcentrations in fruit from the Toowoomba orchard. Fruit harvested from the lowerncanopy took 1.3 days longer to soften than those from the upper canopy when they werenripened immediately at 22oC. The variation in quality of fruit between these canopy factorsnwas related to the different irradiance received.n n n n