The southern blight fungus, Sclerotium rolfsii Sacc., infects many economically important crops (Aycock, 1966). It inflicts heavy losses to the production of peanut and soybean in Taiwan (Liu and Wu, 1972).
The pigmented mature sclerotia of the fungus can resist adverse environmental conditions (Willetts, 1971) such as physical (Lin and Wu, 1968; Liu and Wu, 1971a), chemical (Chet et al., 1967), microbial and enzymatic degradation (Bloomfield and Alexander, 1967; chet and Henis, 1969; Leach and Mead, 1936), but the nonpigmented sclerotia cannot (Chet and Henis, 1969). It was shown that the resistance is mainly due to the melanin or melanin-like pigment deposit on the sclerotial wall (Bloomfield and Alexander, 1967; Potgieter and Alexander, 1966). Furthermore, studies on Aspergillus nidulans (Kuo and Alexander, 1967) established that resistance to microbial lysis is related to the melanin content in the cell wall.
Although many papers have been published on Sclerotium rolfsii Sacc. (Aycock, 1966; Lin and Wu, 1972), relatively few were dealing with the aracterization and formation of the dark pigment of sclerotia. In order to extend information as to the nature of the dark pigment, and factors affecting the pigmentation of sclerotia of S. rolfsii, the present study was undertaken.