The use of zymogram and anastomosis techniques to follow the expansion and demise of two coalescing bare patches caused by Rhizoctonia solani AG-8

Abstract

Pectic zymogram characterization and anastomosis techniques were used to study the distribution of strains of R. solani AG-8 in a large rhizoctonia bare patch. Undisturbed soil cores were removed on nine occasions during the period 1988 to 1992. Identification of the isolates of R. solani from wheat seedlings grown in the cores demonstrated that the patch was a coalescence of two patches, each colonized by isolates of R. solani AG-8 representing different zymogram groups (ZG1-1 and ZG1-5). The demarcation between the two patches remained unchanged while both patches were active. Between the 1989 and 1990 seasons, the pathogen in half of the ZG1-5 patch died, or was reduced to such low levels that it was difficult to detect. In the remainder of the ZG1-5 patch, the pathogen died or was reduced to undetectable levels between the 1990-91 seasons. The ZG1-1 patch was evident at the beginning of the 1991 growing season and the pathogen could be isolated; however, by the end of the season the pathogen could not be isolated. In all these instances the demise of the patch was associated with the disappearance of field symptoms and an inability to isolate the pathogen and therefore the apparent death of the fungus in the soil.