Cationic Surfactants: Potential Surface Disinfectants to Manage Agrobacterium tumefaciens Biovar 1 Contamination of Grafting Tools

Abstract

Nursery production of walnut seedlings is a 2-year process, during which crown gall, caused by Agrobacterium tumefaciens, often develops at grafting wounds. In this study, the spread of crown gall via contaminated tools and the efficacy of several disinfectants against A. tumefaciens were demonstrated. The cationic surfactants benzalkonium chloride (BC), cetyltrimethylammonium bromide (CTAB), and Physan 20 eliminated 100% of the A. tumefaciens population in water suspensions treated at 7, 5, and 2 ppm, respectively. Sodium hypochlorite eliminated 100% of the A. tumefaciens population at 0.5 ppm. Sodium hypochlorite efficacy, however, was reduced by 64% in the presence of total solids (0.7 g/ml) which are commonly found in field situations. At similar concentrations of total solids, the efficacy of cationic surfactants decreased, on average, by only 13%. The minimum effective treatment needed to eliminate A. tumefaciens on infested scalpels was a 5-s exposure to BC or CTAB at 5,000 ppm (0.5%). Infested scalpels treated with BC or CTAB at less than 5,000 ppm caused gall formation in 14 ± 7% of cuts made on Datura stramonium stems. This was significantly less than the tumor incidence (100%) in cuts made with inoculated blades not treated BC or CTAB.