Susceptibility of corn to Rhizoctonia root rot and differences between isolates in pathogenicity

Abstract

Rhizoctonia root rot of corn is a recently occurring disease which has been reported since 1980. To clarify the background of the disease's occurrence, 20 native varieties, 66 foreign varieties and 27 inbred lines were tested for resistance to the pathogen, Rhizoctonia solani AG 2-2. The commercial Fi variety P3358 was used as a standard. All of the 113 varieties or lines were found to be susceptible as well as the standard used. These results showed that corn was originally susceptible to R. solani AG2-2, and the disease's occurrence is not related with the corn variety. On the other hand, the pathogenicity of R. solani AG2-2 isolated from diseased plants of sugar beet and corn was compared through cross inoculation tests. The pathogenicity of corn strains was strong both to corn and sugar beet. The sugar-beet strains were more pathogenic to sugar beet, but clearly weaker to corn.