Characterization and Pathogenicity of Rhizoctonia Species Causing Root Rot and Damping-off on Sugar Beet in Turkey

During 2015–2017 growing seasons, seventy-one isolates of Rhizoctonia spp. were obtained from the samples collected from the sugar beet fields of Konya province, which is one of the most important sugar beet growing areas of Turkey. Anastomosis groups (AGs) of Rhizoctonia spp. isolates were determined by hyphal conjugation with the tester strains and sequence analysis of the rDNA ITS region. The obtained data confirmed the species identity of 61 isolates out of 71 as R. solani (AG-2-2-IIIB, AG-4-(HGI, HGII, HGIII), AG-5, AG-11) and the remaining 10 isolates as binucleate Rhizoctonia (AG-K, AG-A). Pathogenicity tests revealed that AG-2-2-IIIB, AG-4-(HGI, HGII, HGIII) and AG-K isolates were highly virulent on sugar beet. The disease severity of 71 isolates varied between 13 and 100%. Based on the virulence, the isolates formed four categories; (i) 11 isolates: non-pathogenic, (ii) 15 isolates: low virulent, (iii) 6 isolates: moderately virulent and (iv) 39 isolates: highly virulent. To our knowledge, the AGs of AG-4-(HGI, HGII, HGIII), AG-11, AG-A are first reports on sugar beet in Turkey and the AG-5, AG-11 and AG-K are first AG groups for Konya region.