Biological Control of Crown Gall in GF677 Rootstock and Changes in Antioxidant Enzyme Activities

Biological control agents are bacteria that are used to control plant diseases by providing direct biocontrol of pathogens and/or by stimulating the plant’s defense system. The aim of this study was to determine the ability of the five most effective bioagent bacteria to control crown gall on GF677 rootstock, to characterize their biocontrol and plant growth-promoting properties, and to assess the defense-related antioxidant enzyme activities. Bioefficacy tests of bioagent bacteria were carried out for root and stem treatments on GF677 rootstock according to a randomized plot design with five replications and one rootstock in each replication. Three different groups were created as controls. After ~6 months, the number of tumors formed on the roots and the diameter of the tumors formed on the stem were examined. According to the results, the commercial product Nogall had the highest effect in root treatments, followed by strain RK 1 B + 1978. In stem treatments, the lowest tumor diameter was observed with strain 1 B + RK1978. Strain RK 1978 synthesized chitinase, phytase, amylase, protease, and cellulase enzymes but could not synthesize hydrogen cyanide, salicylic acid, and siderophores. The amount of antioxidant enzymes with root and stem treatments in rootstocks increased compared to the control group without any treatment. Molecular analysis identified strain RK 1978 as Bacillus subtilis. Thus, biological control with B. subtilis strain RK 1978 is recommended as a new ecofriendly candidate for the management of crown gall disease.