Anastomosis group and pathogenicity of Rhizoctonia spp. associated with seedling damping-off of sugar beet in China

Abstract

Between 2010 and 2015, 204 Rhizoctonia isolates were obtained from diseased sugar beet seedlings which collected from the sugar beet growing regions of China. On the basis of the morphological characteristics and sequence analysis of the internal transcribed spacers of the ribosomal DNA (rDNA ITS), 166 were identified as multinucleate Rhizoctonia (MNR), and 38 were binucleate Rhizoctonia (BNR), belonging to 15 species, anastomosis groups (AGs) or subgroups. The most prevalent was Rhizoctonia solani AG-4, with 49 isolates attributed to the subgroup HGIII, 47 to HGII, and 45 to HGI, followed by AG-K (31), AG-2-2IIIB (7), AG-A (6), AG-1-1C (4), AG-1-1B (3), AG-2-1 (3), AG-5 (3), AG-11 (2), AG-3 TB (1), Waitea circinata var. circinata (1), W. circinata var. zeae (1), and AG-C (1). Seventy-four representative isolates of all species, AGs or subgroups from different geographic origins were able to cause brown, dry lesions on roots of sugar beet seedlings or even seedling death with the disease incidence and the disease index ranging from 13.3 to 100% and from 1.9 to 97.1, respectively. The AG-4 isolates were the most aggressive on sugar beet seedlings. Moreover, the aggressiveness of the R. solani isolates was higher than that of the other isolates. To the best of our knowledge, this is the first detailed description of the AG composition of Rhizoctonia causing seedling damping-off on sugar beet in China.