Genetic Characterization and Pathogenicity of <i>Rhizoctonia solani</i> Associated with Common Bean Web Blight in the Main Bean Growing area of Argentina

Abstract

Abstract Common bean web blight ( WB ), caused by the fungus Rhizoctonia solani (teleomorph Thanatephorus cucumeris ), is among the endemic fungal diseases of major impact in north‐western Argentina ( NWA ). This study aimed to analyse the genetic and pathogenic diversity of R. solani in Salta, NWA , where 97 isolates were recovered from commercial bean cultivars and wild beans showing WB symptoms in a major bean production area. The isolates were characterized on the basis of specific primers, rDNA ‐ ITS sequences and morphological characteristics. All the isolates were identified as R. solani AG 2‐2 WB , and they exhibited considerable intragroup variation. The phylogenetic tree generated with the ITS sequences confirmed the isolates identification. Aggressiveness of the isolates towards bean seedlings was assessed in the greenhouse. A great variability in virulence was observed among the isolates analysed. On the basis of the disease reaction on foliar tissues, the isolates were grouped into three virulence categories as follows: weakly virulent (30%), moderately virulent (38%) and highly virulent (32%). However, no correlation between virulence and geographical origin was detected. The information generated in this study provides initial data on the population variability of the WB pathogen in north‐western Argentina and represents a valuable contribution to regional breeding programmes aimed to obtain cultivars with durable resistance.