SEASONAL CARBOHYDRATE CHANGES IN DORMANT KIWIFRUIT BUDS

Budbreak and flowering of kiwifruit vines are adversely affected by insufficient winter chilling. Growers use pruning and the dormancy-breaking chemical hydrogen cyanamide to manage vine yields; however, there is still significant seasonal variation. In this study we examined whether sugar levels in dormant kiwifruit bud meristems indicated changes in the status of buds during dormancy and their potential performance in spring. Meristems were sampled from vines at four climatically contrasting sites in New Zealand as well as from canes that had been shaded or girdled during development to manipulate their carbohydrate reserves. Changes in sucrose and hexose levels in meristems indicated changes in bud dormancy status from autumn through to spring. During leaf senescence, sucrose and hexose concentrations in meristems increased rapidly. Accumulation of sugars in meristems ceased in early winter and concentrations remained stable until spring. In spring, before visible bud development, there was a rapid decline in meristem sucrose concentrations but hexose levels increased. Sugar accumulation and subsequent utilisation in meristems began earlier in vines subject to cold temperatures, but peak concentrations were not influenced by temperature. Utilisation of meristem sucrose reserves in spring could be induced by applying hydrogen cyanamide to canes. Peak concentrations of sucrose in meristems during winter were determined by conditions before the onset of dormancy. Canes that were shaded during growth had lower meristem sucrose concentrations during winter than untreated canes, while canes that were girdled in autumn to prevent carbohydrate export had higher meristem sucrose concentrations during dormancy than untreated canes.