SHRIVEL IN KIWIFRUIT

Shrivel is a commercial risk to kiwifruit that may be stored for several months. The recently released ‘Zesy003’ (commonly called Gold9, marketed as Zespri® Charm Kiwifruit) appears more susceptible to shrivel than other cultivars. While Gold9 fruit have a high skin permeance to water, early observations suggested that skin permeance did not account for the fruit’s propensity to shrivel, which was associated with the fruit softening. The relationships between firmness, water loss and shrivel expression were investigated using either storage time or ethylene treatment to alter the relationships. Using storage to obtain soft fruit with relatively little water loss, it was shown that firm fruit take longer to shrivel and have a concomitant higher water loss when shrivel expresses than soft fruit. Alternatively, increasing the softening rate by ethylene treatment, whilst having little effect on the rate of water loss, resulted in the softer, ethylene-treated fruit shrivelling before the slower-softening control fruit. In a comparison between Gold9 and other kiwifruit, soft Gold9 fruit outer pericarp (OP) was found to have a higher water-binding capacity than the OP of ‘Hort16A’ or ‘Zesy002’ (commonly called Gold3, marketed as Zespri® SunGold Kiwifruit). The water status was quantified by magnetic resonance imaging T2 weighted data and by the swelling capacity of a crude ripe fruit OP cell wall preparation. Thus it is concluded that the high propensity for shrivel in Gold9 kiwifruit is associated with a ripe fruit OP that has a high water-binding capacity which prevents mass water flow and re-equilibration of water within the fruit as water is lost.