HEAT TOLERANCE OF DORMANT VITIS-VINIFERA CUTTINGS

Cuttings of one-year-old Vitis vinifera canes of cvs. Cabernet Sauvignon, Merlot, Chardonnay, and Chenin blanc were treated at temperatures between 50-degrees-C and 60-degrees-C for time periods up to 30 minutes to determine their heat tolerance. Survival was estimated by visual observations of shoot and root development of cuttings in the greenhouse after four to six weeks. All cultivars had survival rates equal to controls when treated at 54-degrees-C for 30 minutes. Treatment of samples above 54-degrees-C revealed seasonal and cultivar variability in heat tolerance. Maximum heat tolerance is significantly higher than previously reported. These data indicate that dormant cuttings of Vitis vinifera are capable of surviving extended periods of heat treatment that may be essential for eliminating Agrobacterium tumefaciens (Smith and Townsend 1906) Conn 1942 biovar 3, the crown gall bacterium during asexual propagation.