Damping-off on Broccoli Caused by Rhizoctonia solani AG-2-1·Subset 1 and AG-2-2 IV

Abstract

In June 2016, basal stem rot and underdeveloped broccoli growth occurred in two fields in Hokkaido, Japan. Two isolates obtained from diseased broccoli were identified as Rhizoctonia solani (anastomosis group) AG-2-1·Subset 1 and AG-2-2 IV on the basis of morphology of the cultured samples, temperature-dependent growth characteristics, hyphal anastomosis reactions, and result of PCR analysis with specific primers. In Japan, damping-off on young broccoli plants caused by Rhizoctonia solani AG-1 IC, AG-2-1·Subset 2, AG-2-2 IIIB, AG-4 HG-I, and foot rot of matured broccoli caused by R. solani AG-2-2 IV has been previously reported. We investigated the pathogenicity of the two isolates using three different growth stages of broccoli plants (3-week-old, 8-week-old, and 3-month-old). Inoculated 3-week-old and 8-week-old broccoli developed severe wilt. However, inoculated 3-month-old matured broccoli showed only basal stem rot without wilt symptoms. The observed symptoms and pathogenicity were coincident with that of the damping-off on broccoli. This is the first report of damping-off on broccoli caused by R. solani AG-2-1·Subset 1 and AG-2-2 IV in Japan.