Susceptibility-Inducing Factor(s) in Ethyl Acetate Extract from Germination Fluids of Pyricularia oryzae as Determinants of Basic Compatibility in Rice Blast.

Ethyl acetate (EtOAc) extract of germination fluids of Pyricularia oryzae induced infection by non-pathogenic Alternaria alternata to rice leaves. When spores of A. alternata were inoculated with EtOAc extract to rice leaves, lesions by infection of A. alternata appeared. The higher the concentration of EtOAc extract was, the more the lesions formed. There was no difference in the susceptibility-inducing activity between EtOAc extracts from the compatible race of P. oryzae and the incompatible one to the corresponding rice cultivars. However, the susceptibility-inducing activity of EtOAc extract from P. oryzae was always higher than that from P. grisea at any concentrations tested. From these results we concluded that EtOAc extract from germination fluids of P. oryzae contained susceptibility-inducing factor(s) which were disease determinants of basic compatibility in rice blast disease.