Host Specificity in the GenusAgrobacterium

Abstract

One hundred seventy-six Agrobacterium strains, principally from the USA and isolated from 26 host species in 11 plant families, were inoculated on 11 known crown gall hosts to determine host specificities. No strain was pathogenic on all hosts tested. Sixty-six percent of the pathogenic strains induced tumors or hairy root on 6-8 of 11 host species tested. Twenty-seven strains (nonpathogenic on the initial 11 host species) were nonpathogenic on 3 additional host species. Three percent of the pathogens infected only the host species from which they were originally isolated, which suggests that host origin has a minimal influence on a strain''s host range. In some instances, strains isolated from the same naturally-occurring tumor infected different host species, but some strains failed to infect the host of origin. A. rubi strains were indistinguishable from A. tumefaciens strains on the basis of pathogenicity, and 5 of 8 A. rhizogenes strains formed tumors on some plants and hairy root on carrot. Tomato and Datura stramonium were infected by a greater number of pathogenic agrobacteria (81% each) than any other host species tested. All strains that infected tomato did not infect datura and vice versa. These data corroborate that speciation based on pathogenicity and host specificity is of little taxonomic or practical value.