Abstract
Developmental changes in and factors determining grape berry transpiration were investigated in three genetically diverse Vitis cultivars. Transpiration rates were measured on whole clusters, using a custom-designed cluster chamber, and on individual berries by weighing detached berries over time. Results obtained using the two methods were in good agreement. The chamber method verified the assumption that detaching berries does not alter their transpiration and also showed that rachis transpiration was insignificant compared with whole cluster transpiration. Berry transpiration fluctuated with vapor pressure deficit which determined the driving force. The transpiration rate per berry and, to a lesser extent, the cuticular conductance peaked when berries were red/purple (~13 Brix) and then declined with further ripening. Due to the decline in cuticular conductance during late ripening, the positive linear relationship between berry transpiration rate and surface area weakened after berries turned ripe. Despite the consistent developmental patterns of berry transpiration and cuticular conductance, Concord (V. labruscana) berries consistently had much lower cuticular conductance than Merlot and Syrah (V. vinifera). These results showed that berry transpiration was determined by both external factors (air temperature and relative humidity) and cultivar-specific internal factors (berry surface area and cuticular conductance).
- ©2015 by the American Society for Enology and Viticulture
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