Greenhouse Evaluation of Binucleate Rhizoctonia for Control of R. solani in Soybean

Nine isolates of binucleate Rhizoctonia (BNR) from soybean were screened in the greenhouse for control of Rhizoctonia solani anastomosis groups AG-4 and AG-2-2. Eight of nine BNR isolates, when combined with AG-4 or AG-2-2, significantly increased emergence and survival of soybean (cv. Ozzie) and reduced disease severity compared with AG-4 or AG-2-2 alone. The interaction of soybean cultivar and BNR isolates in the presence of AG-4 and AG-2-2 was also studied using three isolates of BNR, BNR-4, BNR-8-2, and BNR-8-3, and seven soybean cultivars. There was no BNR × cultivar interaction. With AG-4, BNRs significantly increased emergence and survival of cultivars and reduced disease severity, whereas with AG-2-2, BNRs reduced disease severity. Control of R. solani by BNRs was achieved in both a potting soil mix and natural soil. In the initial screening experiments, two BNR isolates reduced emergence, but in all subsequent experiments using three BNR isolates alone, there were no negative effects on germination, survival, or height of soybean plants, and there was no evidence of pathogenicity. In several experiments, BNRs alone significantly increased height of plants compared with the noninoculated controls. BNRs were consistently isolated from hypocotyls and roots, indicating colonization of tissues was associated with control. These BNR isolates may have potential use in management of R. solani in soybean, but will require rigorous testing under field conditions and more extensive studies of their biology.