PCR-DGGE Analysis Proves the Suppression of Rhizoctonia and Sclerotium Root Rot Due to Successive Inoculations

Abstract

The soil-borne pathogens <i>Rhizoctonia solani</i> and <i>Sclerotium rolfsii</i> have emerged as major pathogens of radish (<i>Raphanus sativus</i>) worldwide. The induction of soil suppressive of radish root rot disease was evaluated in soil repeatedly inoculated with <i>R. solani</i>, nonpathogenic binucleate <i>Rhizoctonia</i> sp. AG-A W1 (BNR) and <i>S. rolfsii</i>. The repeated inoculations of soil with <i>R. solani</i> and BNR significantly suppressed the disease severity of <i>R. solani</i> and <i>S. rolfsii</i> compared to the control. In contrast, the repeated inoculation of soil with <i>S. rolfsii</i> significantly suppressed only the pathogen, <i>S. rolfsii</i>. The community structure was examined using PCR-DGGE (polymerase chain reaction denaturing gradient gel electrophoresis) method. The bands of <i>Trichoderma</i> sp. were observed in the first, second and third inoculations of the soil with BNR. Similarly, bands of <i>Trichoderma</i> sp. were observed in the second and third inoculations of the soil with <i>S. rolfsii</i> and <i>R. solani</i>. Compared to the control, disease severity was significantly reduced in the soil repeatedly inoculated with <i>S. rolfsii</i> and <i>R. solani</i> . In conclusion, <i>Trichoderma</i> species were accumulated in specific patterns depending on the applied fungal inoculum in the suppressive soil.