Grapes are temperate crops, frequently damaged by freezing temperatures. The economic losses that result from freezing injury are major problems for grape and wine industries in cold regions. Our central hypothesis is that soluble sugars in grape tissues provides increased freezing tolerance (FT) and the larger sugar, raffinose, accumulates earlier and to higher amounts in cold-tolerant than in cold-sensitive cultivars in response to cold temperature and short-day (SD) photoperiod. The central objective of this dissertation was to characterize the morphological, physiological and biochemical changes in response to cold acclimation (CA) and SD photoperiod. The specific objectives were to: 1) characterize the morphological, physiological and biochemical changes induced by low temperature in cold-tolerant and cold-sensitive Vitis species under controlled conditions; 2) characterize the morphological, physiological and biochemical changes induced by SD photoperiod in cold-tolerant and cold-sensitive Vitis species under controlled conditions and 3) characterize the morphological, physiological and biochemical changes induced by low temperature and SD photoperiod in cold-tolerant and cold-sensitive Vitis species under field conditions.
In response to temperature under controlled environs, grape (Vitis spp) cultivars ‘Frontenac’, ‘Couderc 3309’, ‘Concord’, ‘Cabernet Franc’, ‘Traminette’ and ‘Seyval’ were evaluated. Shoot growth slowed under cold temperature regimes in all cultivars except ‘Concord’. Under the non-acclimating temperature regime, raffinose concentrations were low and similar among cultivars, whereas under CA temperature regimes raffinose accumulation was generally higher and cold-tolerant cultivars accumulated higher concentrations than did cold-sensitive cultivars. Basal leaves and buds accumulated the most raffinose.
In evaluating responses to SD, experiments were conducted in greenhouse using ‘Cabernet Franc’, ‘Couderc 3309’ and ‘Concord’ cultivars. Shoot growth slowed under SD photoperiod in all cultivars. There was also increased periderm formation, endodormancy induction and increased FT. ‘Concord’ was the first cultivar to initiate these changes in response to SD followed by ‘Couderc-3309’ then ‘Cabernet franc’. Under LD, raffinose concentrations were low and similar among cultivars, whereas under SD, raffinose accumulation was higher and cold-tolerant cultivars ‘Couderc-3309’ and ‘Concord’ accumulated higher concentrations than the cold-sensitive cultivar ‘Cabernet franc’.
In the field study we evaluated ‘Couderc 3309’, ‘Concord’ and ‘Cabernet Franc’ and characterized changes in FT and soluble sugar concentrations during the dormant season for two years. Generally basal buds were more FT than middle buds, which were more tolerant than apical buds. The cold-tolerant cultivars ‘Couderc 3309’ and ‘Concord’ had the lowest LT50 compared to the cold-sensitive ‘Cabernet Franc’. There was variation in leaf sugar concentration but leaf raffinose content showed cultivar dependent response associated with early acclimation. Cold-tolerant cultivars showed early responses to SD before low temperatures. In buds, among all sugars, fructose, glucose, sucrose, raffinose and stachyose concentrations had strong correlations with LT50. Basal buds accumulated the most raffinose. Raffinose accumulation was also two to three times higher in the cold-tolerant cultivars than in cold-sensitive. These results suggest that raffinose might be an early step in CA that coincides with early development of FT and can be used as a screening tool for breeding cold-tolerant genotypes and a target for improving FT via gene transfer.