Developmental stage and climatic factors impact more on carbohydrate reserve dynamics of Shiraz than cultural practice

The overwintering carbohydrate reserve status of grapevines has been linked to fruiting responses in the following season, providing a possible avenue for yield management through manipulation of reserve accumulation. Conducted across four consecutive seasons, this study examined the extent to which carbohydrate reserve accumulation could be altered in Shiraz grapevines using existing, or variations of existing, cultural practices. Removal of one-third or two-thirds of clusters at veraison increased average total nonstructural carbohydrate (TNC) concentrations in the wood by 7% relative to control vines after two seasons of treatment and 20% after three. Hedging all shoots to five nodes after harvest reduced wood TNC concentrations by 14% after two seasons and by 27% at flowering in season 3 due to increased carbohydrate mobilization after budbreak. Deficit irrigation treatments applied between fruit set and veraison, or following harvest, had no significant effect on TNC concentrations in the wood, and none of the five treatments evaluated had a consistent influence on carbohydrate reserve storage in the roots. Shoot hedging after harvest had the most pronounced influence on reproductive development, with an increase in bud necrosis after two seasons of treatment and reduction in inflorescence flower numbers after three. While the results indicate there is some scope to alter carbohydrate reserve storage through cultural practice, no treatment substantially altered the seasonal pattern of reserve dynamics relative to control vines. It is suggested that developmental stage or seasonal climatic factors had a stronger influence on carbohydrate mobilization and storage, and that the manipulation of reserve accumulation through cultural practice change may be more suited to effecting longer-term adjustments in vine productivity than short-term responses to seasonal yieldfluctuations.