Characterization and sensitivity to fungicides of Rhizoctonia spp. recovered from potato plants in Bolu, Turkey
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Isolates of Rhizoctonia spp. associated with stem canker and black scurf disease of potato were examined for their anastomosis group, sequence variations in the ITS-5.8S rDNA region, pathogenicity and sensitivity to fungicides. A total of 92 isolates were obtained from diseased tuber, stolon and sprouts of the potato plants, collected from five districts of Bolu province, Turkey. Based on the anastomosis group and the similarity of the nucleotide sequence of the ITS-5.8S rDNA, most of the isolates (81.5%) were identified as AG 3 PT. Other isolates belonged to AG 2-1 (1.08%), AG 2-2 IV (1.08%), AG 4 HG II (8.07%), AG 5 (2.17%), binucleate Rhizoctonia AG A (1.08%) and AG K (4.35%). Pathogenicity tests showed that isolates of AG 3 PT, AG 4 HG II and AG 5 caused similar degrees of disease severity on 45-day-old potato seedlings, whereas AG 2-1 was moderately virulent. AG 2-2 IV and binucleate Rhizoctonia spp. were weakly pathogenic or non-pathogenic on potato seedlings. In this study, anastomosis groups of Rhizoctonia spp. isolates associated with potato in Turkey were characterized for the first time using molecular techniques and classified at the level of subgroups. Furthermore, the effect of selected fungicides was evaluated on disease development caused by soil-borne inoculums of different anastomosis groups (AGs). Flutolanil and Bacillus subtilis QST 713 were found to be most effective against the Rhizoctonia isolates tested. These results revealed significant differences among the fungicides on disease development resulted from the different AGs.