'HORT16A' FRUIT BEAK END SOFTENING AND SHRIVELLING IN CALIFORNIA

'Hort16A' kiwifruit (Actinidia chinensis Planch. var. chinensis) are grown in a range of environments that differ significantly from the environment in New Zealand for which the cultivar was first selected. This has given rise to a range of unexpected fruit responses, including the new disorder “beak end softening” observed in California and Italy in 2003. The disorder developed as softening and then shrivelling at the stylar (beak) end of fruit. In 2004, experiments were established to monitor development of the disorder and identify factors that trigger its development. Fruit grew rapidly for the first 75 days after flowering and continued at a moderate rate until 130 days after flowering. Physiological changes then occurred in the fruit that led to fruit losing water, resulting in beak end softening and then shrivelling. At one orchard, fruit reached a maximum size of 80 g after 130 days, but lost 17 g over the next 60 days leading up to harvest. A simple model of late season water balance of fruit was developed. When calculated with climate data collected during the final 30 days of fruit growth, the model predicted an 8 g water loss from the fruit, which is consistent with the observed 17 g water loss during the final 60 days of growth and suggesting a dominant effect of water loss through the skin on the fruit water balance. This idea was confirmed when fruit still attached to the vine were placed into a high humidity environment inside a plastic bag increased in size, while those outside the bag decreased in size.