The study of the factors which are responsible for host-parasite specificity decided prior to penetration of plant pathogenic fungi

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The powdery mildew fungus, Blumeria graminis an obligate parasite which infects only barley, needs to form an appressorium before it can penetrate the host plant. It is important for the fungus to form an appressorium(APP) on the host plant, because the fungus cannot be incubated on an artificial medium but only on a live host plant. So far it has been thought that APP formation could be observed equally both on the host plant and non-host plant, and the specificity between the fungus and the plants could be determined at the penetration stage or later. However, unlike on the host plant surface, we found that appressorial formation seemed to be inhibited on the non-host plant surfaces. These facts suggest that the specificity between the fungus and the plants could have been determined before the fungus tries to penetrate the plant. In this study, we focused on the chemical components, a decision factor for host-parasite specificity, on various plant surfaces to determine which chemical components are responsible for the appressorial formation of the fungus. Using infrared(IR) spectra and gas I iquid chromatography (GLC), we have identified the substance on the host plant surface that is effective for appressorial formation of the fungus and determined the chemical structure of it. Moreover, based on the results, we have found that the primary germ tube(PGT) which emerges prior to appressorial germ tube(AGT) is responsible for inducing susceptibility of the barley host plant. It acts as a probe to recognize the host plant, and the PGT adheres to the surface prior to AGT's emergence. These results were published in Physiological Molecular Plant Pathology and in "In Pursuit of the Essence of Plant Pathogenesis".