Physiological and Biochemical Seasonal Changes in Vitis Genotypes with Contrasting Freezing Tolerance

In this study, we characterized the influence of genotype and bud position on seasonal changes in freezing tolerance (FT, LT50) and soluble sugars, especially raffinose, and the affect of artificial deacclimation in buds of three field-grown cultivars over two years. Generally, basal buds were more freeze tolerant, and the cold-hardy cultivars Couderc 3309 (3309C; Vitis riparia x V. rupestris) and Concord (CD; V. labruscana) had the lowest LT50 compared to the cold-sensitive Cabernet franc (CF; V. vinifera). Among all sugars, fructose, glucose, sucrose, raffinose, and stachyose had strong correlation with LT50, but distinctive responses associated with bud position and cultivar were related to raffinose. Basal buds accumulated the most raffinose, and raffinose concentrations were two-to three-fold higher in the cold-hardy CD and 3309C than those in the cold-sensitive CF. Furthermore, CD and 3309C started accumulating raffinose with decreasing photoperiod prior to exposure to cold temperature, resulting in an early increase of FT. These results suggest that raffinose accumulation might be an early step in the process of cold acclimation that coincides with early development of FT. We concluded that bud raffinose concentration might be a useful detection tool and a metabolic marker during the early stages of cold acclimation to distinguish various Vitis genotypes with contrasting FT.