Seasonal Accumulation of Starch by Components of the Kiwifruit Vine

The accumulation of starch by various components of 6-year-old kiwifruit vines (Actinidia deliciosa var dehciosa cv Hayward) was recorded over one season Twenty vines were harvested periodically throughout the year and separated into perennial components (fibrous roots, structural roots, stump, stem, cordon, laterals) and current season's growth (shoots, leaves, and fruit) The concentration of starch in the fibrous roots followed a sinusoidal trend Minimum concentrations occurred 98 d after budbreak, while the maximum concentrations occurred 182 d later Corresponding times in the structural roots were approximately 42 d earlier In the above-ground perennial components, elevated concentrations of starch in the cordon, fruiting wood and bark of the stem were evident at budbreak and fruit harvest (approx 220 d later) In the case of the stem, concentrations were greatest at fruit harvest Because the biomass of the perennial components was found to be relatively constant throughout the year, starch concentrations and contents were directly proportional in these tissues For current season's growth, peak concentrations and contents in leaves and shoots were observed at fruitset and fruit harvest, respectively For fruit, starch increased continuously until harvest Approximately 30% of the total starch content accumulated in the perennial components by leaf abscission was lost during winter and early summer Quantitative losses were greatest for the roots Regeneration of the starch pools in the perennial components of the vine occurred from midseason until leaf abscission At the same time, approximately five times more starch was accumulated by the current season's growth, in particular the fruit, than by the perennial components As a result of the difference in the rate of accumulation, the starch content of the current season's growth increased from less than 10% midseason to nearly 60% of the total starch content of the vine by fruit harvest The results were discussed in relation to the carbon economy of the kiwifruit vine, and compared with seasonal trends in starch concentrations found for other deciduous crops