DETERMINING THE RELATIONSHIP BETWEEN FRUIT NUTRIENT STATUS AND THE DEVELOPMENT OF PHYSIOLOGICAL PITTING IN KIWIFRUIT

Physiological pitting is a disorder that develops in ‘Hayward’ and ‘Hort16A’ kiwifruit during low-temperature storage. In ‘Hayward’, pitting is often, but not always, associated with fruit having low calcium (Ca) status. The relationship between fruit mineral nutrient status, and storage quality of ‘Hort16A’ kiwifruit was investigated on mature vines grown in Northland in New Zealand. The aim of this research was to identify which fruit were more susceptible to pitting and to determine whether any fruit nutrients could be related to the development of pitting. The distribution of fruit nutrient status and disorder incidence between vines was mapped in three ‘Hort16A’ orchards (90 vines per orchard). Relationships between fruit nutrient status and physiological pitting were determined using linear regression. In the three orchards, the incidence of pitting ranged from 0 to more than 40% and no convincing relationship between pitting and fruit Ca status was found. In one orchard the five vines with highest pit incidence had low fruit Ca concentrations, but this trend was not consistent across the other two orchards. To investigate whether fruit quality could be affected by increasing fruit Ca concentrations, CaCl₂ (0.5-4.0% w/v) was applied to ‘Hayward’ and ‘Hort16A’ fruit either as a preharvest spray applied up to nine times during the season, or as a postharvest dip. Both pre- and postharvest Ca applications were successful in raising flesh Ca levels in both types of kiwifruit by up to 40%, but had no effect on pitting incidence or fruit firmness after long-term storage.