Abstract

A number of cultivars and selections were subjected as potted plants between grape stage and full flower to frosts of -4.6 and -3.8C in 1981 and 1982, respectively. They were scored for dates of 50% survival and various growth stages, and for raceme development stage at 50% survival date. The SCRI selections P8/12/7, P9/11/13 and P9/11/14, which are related to the tolerant cultivars jebyn and Ben More, tolerated the frosts better than did Ben More. Cut shoots withstood the frosts as well as potted plants. Studies of 20 families derived from 11 lines indicated that tolerance of frost at first flowering was inherited additively and that jebyn and Goliath, the grandparents of Ben More, contributed the highest parental values of tolerance. It is recommended that genotypes are initially tested for frost resistance at a standard developmental stage, such as first flowering, and subsequently tested repeatedly throughout the remaining stages of development.