Weather effects of stalk necrosis in Vitis

A 5-step physiological explanation is offered for correlations found by THEILER and MÜLLER (1986) between aspects of the weather at flowering and the incidence of stalk necrosis in grape. Four of the steps are well supported in the literature and are discussed briefly. The other step proposes that the development of xylem in the peduncle is stimulated by floral evapotranspiration. This postulate is tested with measurements of xylem cross-sectional area in clusters taken from vineyards located in diverse regions of New Zealand for which meteorological data were available. Statistical analysis indicates a clear distinction between material from the climatic extremes and a significant (P = 0.05) correlation between calculated values of evapotranspiration during flowering and peduncular xylem area. The beginning of a physiological explanation for the seasonal effects on the incidence of stalk necrosis in grape has stimulated studies which may allow the selection of non-sensitive varieties