Using forced regrowth to manipulate Chardonnay grapevine (Vitis vinifera L.) development to evaluate phenological stage responses to temperature

Time and environmental conditions, such as temperature and photoperiod, are the main drivers governing grapevine development over the growing season. The most obvious growth periods in grapevines are budbreak, bloom, veraison and berry maturity. The aims of this study were to evaluate the environmental and physiological factors influencing the phenological development of Chardonnay grapevines, and to determine the best fit parameters of degree-day calculation methods for the prediction of various phenological stages. Phenological data retrieved from field vines and vines forced to regrow after heavy pruning and defoliation, whose developmental onset conditions were modified, were used to test and parameterize the degree-day calculation methods. An upper temperature threshold (T-U) was optimized for the different developmental stages, and measures of the radiation use efficiency were derived to adjust T-U during berry maturity. According with the candidate methods, the highest T-U value coincided with bloom (29.8 degrees C), while the lowest was observed at veraison (20.9 degrees C), The RMSE of the model predictions for specific developmental stages ranged from 2 (fruit set) to 9 days (berry maturity). Modifying vine growth periods by forcing vine regrowth allowed evaluation of temperature and physiological factors that influence grapevine development.