FATE OF AGROBACTERIUM-RADIOBACTER K84 IN THE ENVIRONMENT

Agrobacterium radiobacter K84 is an effective, commercially applied, b iological control agent for the plant disease crown gall, yet little i s known about the survival and dissemination of K84. To trace K84 in t he environment, spontaneous antibiotic-resistant mutants were used. Gr owth rates and phenotypes of streptomycin- or rifampin-resistant K84 w ere similar to those of the parental K84, except the rifampin-resistan t mutant produced less agrocin 84 as determined by bioassay. K84 and a strain of Agrobacterium tumefaciens established populations averaging 10(5) CFU/g in the rhizosphere of cherry and persisted on roots for 2 years. K84 established rhizosphere populations between 10(4) and 10(6 ) CFU/g on cherry, ryegrass, and 11 other herbaceous plants. Populatio ns of K84 declined substantially in fallow soil or water over a 16-wee k period. K84 was detected in the rhizosphere of ryegrass located up t o 40 cm from an inoculum source, indicating lateral dissemination of K 84 in soil. In gall tissue on cherry, K84 established populations of 1 0(5) CFU/g, about 10- to 100-fold less than that of the pathogen. Thes e data demonstrate that K84 persists for up to 2 years in a field envi ronment as a rhizosphere inhabitant or in association with crown gall tissue.