Biological Control of Crown Gall with Fungal and Bacterial Antagonists

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Abstract
Pathogenic Agrobacterium strains were inhibited in vitro by 35 different fungi and bacteria that were isolated from nursery soils in Oregon and Washington [USA]. Seven of the 35 antagonists inhibited 6 A. tumefaciens strains in vitro, and also prevented infection of tomato seedlings in the greenhouse. In field tests, isolates of Penicillium, Aspergillus, Bacillus, Pseudomonas and A. radiobacter reduced the incidence of galling on mazzard cherry seedlings by some of the pathogens tested, but none was more effective than A. radiobacter strain 84. With some antagonists, greater reduction in galling was observed when cherry seedlings were inoculated with pathogen mixtures 24 h after inoculation with antagonists. One Penicillium antagonist reduced the incidence of infection of a level below that of the wounded controls when used against some pathogenic strains.