Abstract
Rhizoctonia solani AG-1 IA, R. oryzae, R. oryzae-sativae and R. fumigata, which cause sheath blight, bordered sheath spot, brown sclerotium disease and gray sclerotium disease, respectively, on rice at the late growth stage in paddy fields, were treated with Si and 6 trace elements, (B, Cu, Fe, Mo, Mn and Zn), to assess the effect on mycelial growth, sclerotial germination and pathogenicity on rice. Mycelial growth on glucose asparagine medium was significantly inhibited with 1 and 100 ppm of B, Cu, Mn and Si for R. solani AG-l IA; B, Cu and Zn for R. oryzae; B, Cu, Fe, Mo, Mn and Si for R. oryzae-sativae; and B, Cu, Fe and Mo for R. fumigata. Germination of sclerotia, which were produced on rice straw medium, of R. solani AG-1 IA and R. oryzae-sativae was inhibited by B, Cu, Zn and Si, at 1 and 10 ppm, and R. oryzae was inhibited by only Mo. For R. fumigata, sclerotial germination was inhibited by B, Cu and Zn. Spraying Si at 10 ppm on leaf sheaths of plants at the heading stage resulted in 27% decrease in diseased plant (%) of sheath blight. Moreover, the exposure to Si and Cu reduced lesion area (%) and number on the leaf sheath by 51–53%. These results indicate Si and Cu especially can be used to help control sheath blight and the other Rhizoctonia diseases.
