PHYSIOLOGICAL PROCESSES CONTRIBUTING TO GENOTYPIC VARIATION IN FRUIT COMPOSITION OF ACTINIDIA DELICIOSA

Our aim was to identify the physiological processes contributing to variation in the yield and percent dry matter content (DM) of fruit from Actinidia deliciosa and A. chinensis seedling populations, with the ultimate goal being the selection and production of kiwifruit cultivars with improved flavour attributes. Fruit DM is correlated with the final sugar content and flavour of the fruit at eating ripeness. Comparisons were made between related genotypes producing fruit of low and high DM and a range of fresh weights. No consistent correlations were found between fruit attributes (DM, size, total number) and vegetative traits examined, including leaf area and photosynthetic characters, vegetative biomass and root traits. For a subset of A. deliciosa genotypes, fruit fresh weight and DM were measured from anthesis to maturity, the contribution of the various tissues to total fruit volume recorded, and the concentration of starch, sugars and organic acids measured. There were no correlations between the dates of budburst or flowering and fruit DM. Total fruit DM was not related to differences in proportions of the core or inner and outer pericarp tissues. DM differed significantly between dry matter classes by a small amount from the earliest date of measurements, before starch accumulation had begun, then diverged more strongly during the starch accumulation phase of fruit development. Underpinning these differences were relatively constant rates of dry weight accumulation, usually higher in high DM genotypes, while fresh weight differed strongly between fruit of different final fresh weights only later during fruit development.