Identification and pathogenicity of Rhizoctonia spp. causing wirestem of Betula nigra in China.
During July 2004, wirestem was frequently observed on the seedlings of Betula nigra at Dehong district in Yunnan Province, China. Isolates of Rhizoctonia spp. consistently obtained from their diseased leaves, roots and stems were identified as belonging to binucleate Rhizoctonia anastomosis groups (AG) AG-P and AG-R, and R. solani AG-I IB and AG-4 HG-I, based on cultural characteristics, nuclear staining, anastomisis reaction and analysis of their ITS rDNA region. The percentage of recovery of AG-P, AG-1, AG-R and AG-4 was 48%, 39%, 8% and 3%, respectively. This is the first report of wirestem of red birch cause by binucleate Rhizoctonia AG-P and AG-R, and R. solani AG-1 IB and AG-4 HG-I in China.