Factors affecting infection cushion development by Rhizoctonia solani AG‐1 IA and IB on soybean leaves

Abstract

Infection cushions were formed by isolates of Rhizoctonia solani, anastomosis group 1 IA (AG‐1 IA, aerial blight) and AG‐1 IB (web blight) on leaves of all 10 soybean cultivars tested. Isolates of AG‐1 IA and IB did not form infection cushions on soybean leaf surface replicas of either resistant or susceptible cultivars. More infection cushions were formed by isolates of AG‐1 IA and IB on collodion membranes placed over leaves of susceptible cultivars compared with resistant cultivars. Isolates of AG‐1 IC. AG‐4 and AG‐5, also formed infection cushions on soybean leaves. However, the isolates of other anastomosis groups did not form infection cushions on soybean leaves. Differential induction of infection cushion formation by the leaves of various plant species was observed, AG‐1 IA formed infection cushions on more graminaceous hosts than AG‐1 IB, Our results suggest that a chemical stimulus is needed for infection cushion formation. Glucose and 3‐O‐methylglucose repressed disease severity caused by AG‐1 IA and IB isolates to the same extent. Disease severity and the number of infection cushions formed on leaves of ten soybean cultivars were correlated. Fewer infection cushions were formed on resistant cultivars than on susceptible cultivars.