Molecular characterization and pathogenicity of Rhizoctonia spp. isolates from a tobacco growing area in northwestern Argentina

Abstract

In Argentina, over 60% of the tobacco crop is grown in the northwestern part of the country. In this region, Rhizoctonia solani can cause serious disease problems that result in losses in yield and quality. We collected 35 isolates of Rhizoctonia from 32 tobacco fields in Northwestern Argentina and characterized the isolates by means of morphological and molecular approaches. Based on variability in the ITS region, isolates were identified as R. solani (80%), Waitea circinata var. zeae (Rhizoctonia zeae) (8%) and binucleate Rhizoctonia (8%). Most isolates of R. solani belonged to the anastomosis groups (AG) AG 4 HG-I (44%), AG 2-1 (41%) and AG 4 HG-III (13%). Isolates of binucleate Rhizoctonia belonged to AG-F and AG-P of Ceratobasidium sp. Greater morphological variability was observed within isolates of AG 2-1 and AG 4 HG-III than in isolates of AG 4 HG-I. The aggressiveness of isolates on tobacco seedlings was determined under greenhouse conditions. Isolates of AG 2-1 were the most aggressive on leaves (target spot), while isolates of AG 4 HG-I were the most aggressive on stems and roots, causing damping-off. This is the first in depth study of Rhizoctonia on Virginia tobacco cultivars in the major production areas of Argentina.