CHANGES IN ABSCISIC-ACID CONCENTRATION, SURFACE CONDUCTANCE, AND WATER-CONTENT OF DEVELOPING KIWIFRUIT

Seasonal changes in abscisic acid (ABA) concentration, surface conductance to water vapour and water content, were measured in developing fruit from the upper and lower canopies of 8 year old kiwifruit vines (Actinidia deliciosa var. deliciosa). Three stages were apparent for the accumulation of ABA by the developing fruit. The first stage was characterised by a high initial concentration of ABA in the skin, coupled with high surface conductance of the fruit, suggesting that ABA accumulation during the first 1-2 weeks after anthesis was via the transpiration stream. A marked reduction in concentration of ABA during the second stage of accumulation was consistent with dilution by fruit growth. The constancy in the concentration of ABA during stage three (from Week 12 until harvest) suggested that ABA was, in some way, linked to photosynthate loading into the fruit. The larger quantity of ABA in fruit from the upper canopy, which had greater dry matter gains, is consistent with this conclusion. The positive relationship between ABA concentration and rapid fruit growth suggests that ABA may have a role in the allocation of assimilates to fruit. Changes in water content of kiwifruit followed closely the stages of fruit growth. A close relationship between the water content and shape of the developing fruit and published data for glucose in kiwifruit, is consistent with fruit enlargement being osmotically driven. The reduction in percent water content during the latter stages of growth, especially for fruit from the upper canopy, could largely be accounted by the large build-up of starch during that period. The surface conductance of the fruit declined rapidly during the first 9 weeks after anthesis. The conductance then remained relatively constant at low levels until harvest. Compared with apple, the surface conductance of kiwifruit (0.1-0.8 mmol H2O m-2s-1) was up to ten times greater during the early stages of growth.