Dr. Toshiyuki Usami is a phytopathologist. One of his research themes is "Genetic studies on pathotypes of Verticillium dahliae". V. dahliae causes wilt disease on various plants. Although the host range of this phytopathogenic fungus is wide, the pathogenicity differs among isolates. Japanese isolates of V. dahliae is divided into several pathotypes on the basis of their pathogenicity. For example, tomato pathotype is pathogenic on tomato; but is nonpathogenic on sweet pepper. Dr. Usami is investigating the pathogenicity-differentiating mechanisms of V. dahliae by comparing genetic profiles among pathotypes. He obtained several "tomato pathotype-specific" DNA sequences, and revealed that these sequences are located on a same chromosome. Studies on expression of disease-resistance genes in plant, analysis of microbial community in soil using DNA sequences and characterization of new variety of fungal pathogen are his work, also.