BUD RESPIRATION AND DORMANCY OF KIWIFRUIT (ACTINIDIA-DELICIOSA)

Kiwifruit (Actinidia deliciosa (A. Chev.) C. F. Liang & A. R. Ferguson ) is a perennial vine which requires winter chilling during the dorman t period before it will flower and crop adequately. Quantifying the im pact of winter temperatures is difficult because the first detectable responses of the vine are floral initiation and bud break which do not occur until spring. We believed that the respiration rate (R-D) of bu ds of kiwifruit during the dormant period might provide an early indic ation of the changes in bud stale associated with chilling. R-D was me asured during autumn, winter and spring on buds collected from three c ontrasting regions of New Zealand. The R-D of buds collected from thes e regions during the autumn were consistently different. Buds from the coolest region had the highest R-D. These differences which were smal l, but consistent, were apparent by the time measurements started al t he beginning of May. The autumn R-D was correlated with the proportion of floral shoots and numbers of flowers per winter bud, and to a less er extent, the amount and spread of bud break. These correlations focu s attention on the importance of this period in determining 'winter' c hilling responses. It raises the possibility of R-D being used as a pr edictor of vine performance as early as 17 weeks before bud break. A r apid increase in R-D was detected during spring. This occurred 3-6 wee ks prior to bud break and coincided with developmental changes within the buds. Changes in R-D in early spring were correlated with the timi ng and spread of bud break and the proportion of shoots that bore flow ers, but not flower numbers. To provide a comparison of the potential use of R-D as an index of vine response to chilling, bud break and flo wering parameters were regressed against mean air temperature during t he period from May to July. The correlations with air temperature were as useful as those based on the autumn or spring R-D but were availab le only 6-9 weeks before bud break. The autumn R-D can be obtained at least 8 weeks earlier than mean winter temperature data and this may b e an important advantage if this information can be used for forecasti ng vine responses to chilling. (C) 1997 Annals of Botany Company.