Effects of Fumigation and Biological Control on Infection of Indexed Crown Gall Free Grape Plants

Abstract

Indexed Agrobacterium-free grape plants, including cultivars resistant and susceptible to crown gall, were planted in an Agrobacterium-infested vineyard soil. The presence of agrobacteria in indexed plants was examined at seasonal intervals between summer 1989 and spring 1991. Agrobacteria became detectable 16 months after planting. More Agrobacterium cells were isolated in spring after the root pressure forced the sap upwards into the trunk. This indicated that the primary source of inoculum was from infested soil. Fumigation with Vorlex decreased the initial inoculum level, and the fumigant and the antagonist A. radiobacter HLB-2 both reduced the occurrence of infection and tumor development.