REGRESSION ANALYSIS OF WINTER HARDINESS OF GRAPE cultivars from Ya.I. Potapenko don ampelographic collection
The change in wintering conditions is an important aspect of the climate change for viticulture. The work aimed to build regression models of the budbreak percentage dependence on weather and climatic factors in the Lower Don region. The object of the study was analytical data collected in the period from 1981 to 2017 from studying 171 cultivars cultivated in the Ya.I. Potapenko Don ampelographic collection. Three cultivar groups of different origin were singled out: inter-specific hybrids obtained involving Vitis amurensis Rupr. (20 cultivars), inter-specific hybrids obtained with Vitis labrusca L. (19 cultivars), Vitis vinifera L. species and hybrids of intra-specific origin Vitis vinifera L. (81 cultivars). For each year, the budbreak percentage mean values were calculated for each group and for the sample as a whole; regression models were built. In 1981-2017 there was a 0.27-0.63% per year increase in the budbreak percentage for all the studied groups. The plants demonstrated better overwintering results after warm and dry vegetation conditions as compared to cold and wet wintering conditions. The budbreak percentage was sensitive to extreme temperatures. Thus, the uncovered cultivars were sensitive to the number of days with temperatures below -20°C; the covered cultivars were sensitive to the minimum average daily temperature during winter. The budbreak percentage increase tendency was associated with reduced rainfall in July and temperature increase in August, and was partially offset by a tendency towards increased extreme temperatures.