1999 Volume 65 Issue 6 Pages 571-575
To ascertain the feasibility of integrating a bactericide-resistant biocontrol agent into conventional bactericide sprays to control soft rot of cabbage under field conditions, detached petioles of Chinese cabbage were treated with either oxine-copper or basic copper sulfate followed by Erwinia carotovora subsp. carotovora strain 2TQ-19-9 or A-f-39. The survival rate of the more copper-resistant 2TQ-19-9 was higher after both treatments compared to the less resistant strain A-f-39. A rifampicin-resistant derivative of 2TQ-19-9, 2TQ-rif-4, was used for a subsequent field trial. Only 1.2% of the sensitive strains survived on Chinese cabbage plants treated in the field with oxine-copper as compared to 11.2% of the resistant strain one day after their application. Subsequent survival rates of the sensitive and resistant strains were not significantly different. A second application of the bactericide again reduced the population of the sensitive strain but not as much as did the initial application. This second application, however, caused an increase in the population of the resistant strain. The sensitive strain could not survive well after treatment, with the oxine-copper-bacterial mix spray and its population decreased to 2.25cfu/g fresh weight of plant tissue. In contrast, the resistant strain survived to a final concentration of 1.06×103cfu/g fresh weight of plant tissue.