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

Seasonal changes in abscisic acid (ABA) concentration, surface conduct ance to water vapour and water content, were measured in developing fr uit from the upper and lower canopies of 8 year old kiwifruit vines (A ctinidia deliciosa var. deliciosa). Three stages were apparent for the accumulation of ABA by the developing fruit. The first stage was char acterised by a high initial concentration of ABA in the skin, coupled with high surface conductance of the fruit, suggesting that ABA accumu lation during the first 1-2 weeks after anthesis was via the transpira tion stream. A marked reduction in concentration of ABA during the sec ond stage of accumulation was consistent with dilution by fruit growth . The constancy in the concentration of ABA during stage three (from W eek 12 until harvest) suggested that ABA was, in some way, linked to p hotosynthate loading into the fruit. The larger quantity of ABA in fru it from the upper canopy, which had greater dry matter gains, is consi stent with this conclusion. The positive relationship between ABA conc entration and rapid fruit growth suggests that ABA may have a role in the allocation of assimilates to fruit. Changes in water content of ki wifruit followed closely the stages of fruit growth. A close relations hip between the water content and shape of the developing fruit and pu blished data for glucose in kiwifruit, is consistent with fruit enlarg ement being osmotically driven. The reduction in percent water content during the latter stages of growth, especially for fruit from the upp er canopy, could largely be accounted by the large build-up of starch during that period. The surface conductance of the fruit declined rapi dly during the first 9 weeks after anthesis. The conductance then rema ined relatively constant at low levels until harvest. Compared with ap ple, the surface conductance of kiwifruit (0.1-0.8 mmol H2O m-2s-1) wa s up to ten times greater during the early stages of growth.