Effect of inoculum type and anastomosis group of Rhizoctonia solani causing wirestem of cabbage seedlings in a controlled environment

Three-week-old seedlings of cabbage cv. Bravo were inoculated with either infested cornmeal-sand cultures (9.1 x 104 colony-forming units per kg soil) or selerotia (50 per kg soil) of isolates of Rhizoctonia solani anastomosis group (AG) 2-1 (five isolates) or AG4 (five isolates). Wirestem incidence (percentage of diseased and dead plants), severity on hypocotyls and roots (rated on a l-lO scale), and plant fresh weight were assessed two weeks after inoculation. Wirestem incidence and severity were greater and plant weight was lower with cornmeal-sand inoculum than with sclerotial inoculum. As a group, isolates belonging to AG4 were significantly more virulent than those of AG2-1 under conditions of this study. Within each AG, isolates could be separated based on virulence with either inoculum type. Use of sclerotial inoculum of a virulent isolate of R. solani AG4 or AG2-1 would provide the most practical means to screen Brassica oleracea germplasm.