Fruit degreening in different cultivars of kiwifruit

The global trade in kiwifruit (Actinidia chinensis) developed with the green-fleshed 'Hayward' as the predominant cultivar. More recently, alternative cultivars have become available, including those with yellow flesh. 'Hayward' is largely considered not to degreen, despite evidence that it does so slowly. In contrast, yellow-fleshed cultivars degreen fully to reveal their background pigmentation. The degreening of five cultivars of kiwifruit, 'Zesy002', 'Zesy003', 'Zesh004', 'Tomua' and 'Hayward', on and off the vine, has been investigated with respect to fruit development on the vine and temperature when off the vine. 'Zesy002' and 'Zesy003' fruit may degreen fully on the vine, while 'Zesh004', 'Tomua' and 'Hayward' show less colour change. This may be associated with both the genetics and timing of fruit development. Off the vine, 'Zesy002' and 'Zesy003' fruit harvested when green continued to degreen, although the rate was temperature dependent. In contrast, off the vine there was little degreening in 'Zesh004' fruit and virtually no degreening in 'Tomua' and 'Hayward'. However, there was significant chlorophyllase activity in the fruit of all cultivars. In 'Zesy002' and 'Zesy003' fruit, chlorophyllase activity decreased as fruit fully degreened. In 'Hayward' and 'Tomua' fruit, the coexistence of high levels of chlorophyll and chlorophyllase activity suggests that chlorophyllase activity is not the only determinant of fruit degreening. There appear to be two aspects to the differences in degreening among cultivars: the inherent genotype difference in capacity to degreen, and the temperature dependence of the degreening process.