Modeling the effect of temperature on bud dormancy of grapevines

摘要

Dormancy is an evolutionary strategy to overcome adverse conditions during winter through the interruption of growth and metabolism. Winter dormancy is divided into two phases: endodormancy when bud growth is inhibited internally, and ecodormancy when adverse environmental conditions impede growth. The study of winter dormancy is limited because the onset and transition between the two dormancy phases do not have any visual symptoms. Therefore, the goal of this study was to develop a model to predict the occurrence of the onset and release of dormancy phases and budbreak in grapevines 'Cabernet Sauvignon' and 'Chardonnay'. An integrated phenological model was developed assuming that the shortening of the photoperiod induces the onset of endodormancy when a critical day length specific for each cultivar is reached. Then, a period of exposure to chilling temperatures induces the transition from endodormancy to ecodormancy, followed by a period of warm temperatures that forces budbreak. The model showed that 'Cabernet Sauvignon' has a longer endodormancy period caused by the cultivar-specific sensitivity to shorter photoperiods, as well as a slower completion of the chilling requirements compared to 'Chardonnay'. For both cultivars, relatively high temperatures were effective for chilling accumulation. The base temperature for heat effect accumulation was the same for the two cultivars at 5.6 degrees C, while 'Chardonnay' had a lower heat requirement causing a shorter ecodormancy period and earlier budbreak compared to 'Cabernet Sauvignon'. Although the trendline for predicted-versus-observed budbreak dates was significantly different from the 1:1 line, it showed a high R-2 value of 0.92. The model also presented high accuracy and performance based on other evaluation statistics such as a correlation coefficient of 0.96, an RMSE of 5 days, and an agreement index of 0.95. Future updates of the model should add the temperature effect on the estimation of endodormancy onset.