MORPHOLOGICAL, GENETIC CHARACTERIZATION AND PATHOGENICITY OF Rhizoctonia solani ISOLATES FROM COTTON IN BRAZIL

The Rhizoctonia solani is an important pathogen in cotton crop associated with damping-off disease. The variability among isolates are extremely important, because differences exist between anastomosis groups, taken as those isolates capable of exchanging genetic information with each other. Morphological characterization, when confirmed by genetic characterization provides concrete information about the isolates distribution when it acts like a pathogen. Our study was to identify and characterize the anastomosis groups in Brazil and confirm them by genetic characterization. We considered 51 Rhizoctonia solani isolates aiming to characterize the anastomose group and determine their pathogenicity. The morphological characterization was done observing the number of cores, colony morphology and identification of anastomosis groups (AG). In genetic characterization were sequenced and analyzed the genomic fragments containing the 5.8 S, ITS1 and ITS2 regions and compared them to Rhizoctonia isolates listed in the GenBank. The pathogenicity was evaluated for the disease severity, using the scale of infection with grades ranging from 1 to 4. Considering the AG we identified 36 of 51 isolates as AG-4 and two isolates as AG-7 and 13 isolates were listed as unrated. In molecular analyses were confirmed those 36 isolates and were identified more 10 isolates as AG-4. All the AG-7 isolates were confirmed and we found one more considering the molecular analyses. For the pathogenicity was found that five strains did not differ from the control. Intermediate virulence and high virulence were observed in 16 and 24 isolates, respectively with averages from 2.52 to 3.3 and from 3.4 to 3.9.