Dormancy dynamics of ‘Tannat’ grapes in warm-winter climate conditions

Abstract The objective of this study was to investigate the dormancy dynamics of ‘Tannat’ grapes in warm-winter climate conditions, as well as correlating it to chill and heat accumulation. Single-nodes of 1-year-old canes were sampled throughout fall-winter, corresponding to different chill accumulation periods, and placed in growth chamber as means to evaluate the percentage of budburst, the time of 50% budburst (DD50), the time (days) to reach DD50, maximum budburst (MB), and average time to budburst (ATB). For each sampling date, chill accumulation was calculated according to several models in order to detect the most suitable for our climatic conditions. Heat accumulation, expressed as growing degree hours (GDH) was also calculated in order to predict budburst in the field from the completion of endodormancy and maximum budburst. Our results show that the single-node test is effective to represent the dormancy dynamics of ‘Tannat’ grapes in warm-winter conditions. Besides, the DD50 is a valid concept to determine endodormancy completion, which was fulfilled with approximately 100 chill hours below 7.2 °C (CH7). Even though the CH7 was the most consistent model, our results suggest that endodormancy is induced by temperatures greater than 7.2 °C in late summer/early fall. The growing degree hours (GDH) accumulated from the end of endodormancy and maximum budburst is fairly accurate to estimate actual budburst in the field. Chill accumulation is inversely correlated with time to reach DD50 and ATB, i.e., as chill accumulation increases time to reach DD50 and ATB decreases.