The effect of resistance of rootstocks to crown gall (Agrobacterium spp.) on the susceptibility of scions in grape vine cultivars

Abstract

The effects of two grapevine rootstocks on susceptibility of grafted scions to crown gall (Agrobacterium vitis and Agrobacterium tumefaciens) was investigated in greenhouse and field experiments. The incidence of crown gall on a susceptible grape scion cultivar (Vitis vinifera, cv. Kiralyleanyka) was not affected by grafting it on a crown gall resistant rootstock (Vitis riparia, cv. Gloire) or on a susceptible rootstock (V. berlandieri × V. riparia, cv. Teleki 5C) when the inoculated vines were observed over a 2‐month period in the greenhouse. Weights of galls that were induced by six of eight strains of Agrobacterium (six A. vitis and two A. tumefaciens) were not significantly different, but A. tumefaciens strain 16/6 and A. vitis strain 2/3 produced significantly larger galls on Kiralyleanyka vines that were growing on their own roots or were grafted on 5C than on those grafted on Gloire. When the same vines were planted in the field and observed over a 4‐year period, no differences in incidence of crown gall were appa_rent until the third and fourth years, when vines grafted on Gloire had less crown gall than vines on 5C. By that time, the natural symptoms (galls along the trunk) of the disease appeared, coinciding with the decline of whole vines. In another field experiment, with naturally infected scions of V. vinifera, cv. Blau Frankisch (susceptible), crown gall was appa_rent on vines grafted on both rootstocks after 2 years, but in the fifth year 79% of the vines on 5C had crown gall whereas only 9% on Gloire showed symptoms. After the appearance of typical natural symptoms, vines showed reduced vigor with substantial loss of trunks and entire vines. During this period, many vines on 5C died as compared with only a few on Gloire. By the end of the sixth year, 13% of the originally planted vines on 5C and 82% on Gloire were alive, and although many pathogenic strains of Agrobacterium spp. were isolated from the roots of 5C, none was isolated from Gloire.