Determining the chill requirements for Sauvignon blanc budburst

Uniform budburst of the grapevine normally requires a period of chilling necessary to satisfy endodormancy then a period of warming to overcome ectodormancy. Chill and heat requirements differ among grapevine cultivars and it is important to assess (i) the potential variability of budburst which may lead to non-uniform fruit development and (ii) the susceptibility of vines to early season frost, especially under winter temperature conditions that may results from climate change. The aim of this study was to characterise the temperatures and duration of chill required to satisfy the dormancy of the grapevine cultivar Sauvignon blanc. Single node Sauvignon blanc cuttings were collected shortly after harvest, and subjected to a range of base temperatures -2, 4, 8 and 20°C – and durations - 0 (no chilling – continuous at 20°C), 119, 330, 592, 784 and 1007 hours at each chilling temperature. After each chill duration, the cuttings were transferred to 20°C. Chill requirements were met (measured by 50% of bud burst) when cuttings were subjected to temperatures of less than 4°C for 330 hours or more. The time to bud burst under warm conditions (20°C) was reduced when the chill duration was longer than 330 hours at 2 and 4°C. Likewise the uniformity of budburst was increased. At 8°C or 20°C less than 50% of buds burst, regardless of duration. This indicates a base temperature of less than 8°C is required for Sauvignon blanc to break endodormancy and higher temperatures will result is reduced and irregular budburst. Furthermore, this value differs to those reported for other cultivars and emphasizes the need to characterise the chill requirements of individual cultivars. The results are being integrated into a model based on chill and heat accumulation to predict budburst for Sauvignon blanc