Genetics of Fruit Softening

Abstract

Ripe kiwifruit have a soft melting texture that, combined with distinctive flavours, aromas and colours, has made the fruit an international success. A key feature of successful New Zealand cultivars, e.g. Actinidia chinensis var. deliciosa ‘Hayward’ and Actinidia chinensis var. chinensis ‘Hort16A’, is their ability to be stored for long periods both at ambient temperature and in cool storage. In these cultivars, the majority of fruit softening occurs in the apparent absence of ethylene production. In contrast, late ripening is associated with autocatalytic ethylene production, where fruit enter the eating window and then proceed to senescence. The decline in fruit firmness during kiwifruit ripening is largely attributed to the disassembly of the fruit cell wall , which provides cellular rigidity and is responsible for intercellular adhesion. In this review, we consider the key genetic changes that occur during fruit softening in kiwifruit and relate these to changes in the cell wall during the same time period. Understanding these relationships is essential to the development of new kiwifruit cultivars with good postharvest characteristics, as long-storing fruit are relatively rare in A. chinensis var. chinensis and A. chinensis var. deliciosa germplasm material, and most other Actinidia species are characterised by rapid softening and limited shelf life.