EFFECTS OF FUMIGATION AND BIOLOGICAL-CONTROL ON INFECTION OF INDEXED CROWN GALL FREE GRAPE PLANTS

Indexed Agrobacterium-free grape plants, including cultivars resistant and susceptible to crown gall, were planted in an Agrobacterium-infes ted vineyard soil. The presence of agrobacteria in indexed plants was examined at seasonal intervals between summer 1989 and spring 1991. Ag robacteria became detectable 16 months after planting. More Agrobacter ium cells were isolated in spring after the root pressure forced the s ap upwards into the trunk. This indicated that the primary source of i noculum was from infested soil. Fumigation with Vorlex decreased the i nitial inoculum level, and the fumigant and the antagonist A. radiobac ter HLB-2 both reduced the occurrence of infection and tumor developme nt.