Method of Evaluation on the Degree of Resistance of Grapevine and Resistance of Grapevine Cultivars to Crown Gall Disease Caused by Agrobacterium tumefaciens biovar 3

Abstract

Inoculation method for evaluating the degree of resistance to crown gall disease in grapevine, criteria for the evaluation of the degree of resistance, and classification of the degree of resistance in the major 60 cultivars of grapevine were examined. Second and third internodes of current shoots developed from nursery plants were inoculated at several sites by the needle prick inoculation method with a suspension (ca. 2×10⁸cfu/ml) of A. tumefaciens biovar 3, and were subsequently kept at 23°C for about 30 days. The diameter (2r) of the crown galls formed on the shoot was measured and the r²π value was calculated. Resistant “Delaware”, moderately resistant “Rose Ciotat”, and susceptible “Kyoho” cultivars should be inoculated at the same time when the degree of resistance in grapevine was evaluated. Then criteria for the evaluation of the degree of resistance were made as follows. When the index number against the r²π value of the crown galls formed on susceptible “Kyoho” cultivar was set at 100, the cultivars with an index number ranging from 0 to 20 were scored as resistant, those with index numbers from 21 to 60 were scored as moderately resistant, and those with an index number exceeding 60 were scored as susceptible. Based on the degree of resistance, the major 60 cultivars of grapevine inoculated with A. tumefaciens biovar 3 were classified into resistant (11 cultivars), moderately resistant (30 cultivars) and susceptible (19 cultivars) groups.