Comparison of the virulence and cognate virulence factors of multinucleate, binucleate and uninucleate Rhizoctonia isolates, causing sheath blight on maize plants

Abstract

Maize sheath blight is a destructive disease of maize world-wide. The causal pathogens of the disease include multinucleate, binucleate and uninucleate Rhizoctonia isolates according to the latest reports. In this study, the virulence and virulence factors of one uninucleate, two binucleate and nine multinucleate Rhizoctonia isolates were compared. The results showed that there was significant difference in the virulence of the tested Rhizoctonia isolates on maize, with multinucleate Rhizoctonia isolates the most virulent, binucleate Rhizoctonia isolates moderate and uninucleate Rhizoctonia isolate the lowest. The cell wall-degrading enzymes (CWDEs) and phytotoxins of the tested isolates were extracted and their enzymatic or biological activities were detected. The correlation coefficients between the enzymatic activity of polymethylgalacturonase (PMG), polygalacturonase (PG) and endo-β-1,4-glucanase (Cx) and pathogenicity of the isolates were 0.8210, 0.7314 and 0.8497, respectively. The correlation coefficients between the inhibition rate of corn seed germination and root growth caused by the phytotoxins and pathogenicity of the isolates were 0.9257 and 0.9690, respectively. These results indicated that CWDEs and phytotoxins likely act as virulence factors during infection. In conclusion, the lowest virulence of the uninucleate Rhizoctonia isolate JN on maize is possibly due to the low activities of CADEs and phytotoxins.