Non-differential interaction between isolates of Rhizoctonia solani and flax cultivars

Abstract

The pathogenicity of 24 isolates of Rhizoctonia solani (7 isolates from anastomosis group AG-2 and 17 from AG-4) was evaluated on 10 flax cultivars under greenhouse conditions. Survival, plant height, and dry weight were used as criteria to evaluate pathogenicity. Analysis of variance (ANOVA) showed that the cultivar was a highly significant source of variation in all the tested parameters (P < 0.0002). Isolate was always a highly significant source of variation in all the tested parameters (P = 0.0000). Cultivar x isolate interaction was always a nonsignificant source of variation. The results of the ANOVA in the present study suggest that physiologic specialization did not occur within R. solani isolates pathogenic on flax. They also imply that resistance of the tested cultivars was only horizontal, and there were significant differences among cultivars in this type of resistance. Similarly, pathogenicity of the tested isolates was only aggressiveness, and the isolates significantly differed in this type of pathogenicity. A hierarchical cluster analysis was conducted in order to group the isolates according to disease variables measured on the tested cultivars. Cluster analysis divided the isolates into groups; however, grouping the isolates was not related to their geographic origin nor the AG.