Dormancy, Cold Hardiness, and Spring Frost Hazard inVitis amurensisHybrids under Continental Climatic Conditions

Abstract

Seven <i>Vitis amurensis</i> hybrid selections were studied for intensity of dormancy, winter hardiness, and earliness of budbreak during the 2000/2001 dormant season under continental climatic conditions in southern Missouri. Results of a budbreak assay demonstrated that buds from six of the seven hybrid selections could be released from dormancy under forcing conditions as early as October. Throughout November and December, the intensity of dormancy was lower in all <i>V. amurensis</i> hybrids than in the French-American hybrid variety Vignoles. These observations suggest that endodormancy is relatively short in <i>V. amurensis</i> hybrids. In these grapes, the first evidence of bud growth in the field was observed in early January, two to three weeks earlier than in Vignoles. Bud and shoot growth were several phenological stages in advance of Vignoles throughout late winter and early spring. The examination of buds at the end of the dormant season revealed that primary bud mortality was lower (<i>p</i> ≤0.05) in three of the <i>V. amurensis</i> hybrid selections than in Vignoles. A late spring frost event, however, destroyed large numbers of emerging shoots on the hybrid selections, killing 37 to 93% of the young shoots at node positions 1 through 5. All seven of the <i>V. amurensis</i> hybrid selections suffered greater spring frost damage (<i>p</i> ≤0.05) than Vignoles, which was at a considerably less advanced phenological stage. The data suggest that <i>V. amurensis</i> has limited value as a genetic resource in continental North America, where winters are characterized by widely fluctuating temperatures and spring frosts are common.