School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemThe effect of temperature on the timing of grapevine phenology( 2021)Climate change and associated temperature increase is having a profound impact on the timing of grapevine phenology. The expectation that this will continue necessitates grape growers to adapt to climate change. Part of adaption will be understanding what cultivars to plant in existing and new vineyard sites, specific knowledge of which is currently lacking. This thesis aimed to increase our knowledge of the phenological response of grape cultivars to temperature, with the longer-term goal of assisting future selection of cultivars. Using historical data from four commercial vineyards in climatically different regions in Victoria, Australia, and using advanced statistical modelling techniques, the study showed that the phenological stages maturity, veraison and flowering had advanced as related to springtime maximum temperature and there are significant differences between cultivars and their rate of advancement. Later ripening cultivars advanced maturity at a greater rate than earlier ripening cultivars at the same vineyard. Yet, the same cultivar at different vineyards, advanced maturity at a greater rate in the cooler vineyard. A significant delay in the timing of maturity was also demonstrated for one cultivar. These findings provide explanations for the observation of time compression of the harvest period and noted that as temperature further increases, vines will move beyond their optimal growth temperature range for growth and show the impact of heat stress with delayed rates of phenological advancement. Comparisons of the rates of advancement for a given phenological stage across different vineyard regions showed that the response of cultivar to temperature was nonlinear and differed according to the vineyard grouping and the temperature. The intervals between the four major phenological stages, budburst, flowering, veraison and maturity were also investigated. It was found that the budburst to flowering interval was more highly correlated to temperature than intervals between other phenological stages and had shortened at a significantly greater rate than the flowering to veraison and veraison to maturity intervals, as related to springtime maximum temperature. The relationship between temperature and budburst to flowering interval was best described by a curve, indicating that as the average daily maximum temperature during this interval increases, the decrease in interval length will slow and plateau. By extension, this also indicates that the observed advancement in maturity timing, as related to springtime maximum temperature, is expected to slow and plateau with future increases in temperature. These results will inform future management decisions as the wine industry responds to the challenges of a changing climate and show that cultivar diversity will be an important tool in these adaptation strategies.