Tetsu Tsurushima

Colletofragarones A1 and A2, novel germination self-inhibitors from the fungus Colletotrichum fragariae

Abstract The structures of colletofragarones A1 and A2, germination self-inhibitors from Colletotrichum fragariae, have been elucidated by spectroscopic analysis.

Self-germination inhibitors fromColletotrichum fragariae.

The conidial germination ofColletotrichum fragariae in water was dependent on population, size germination was inhibited at higher concentrations of conidia in water. The inhibition was considered to be caused by some germination-inhibiting substances exuded from conidia, since the germination did occur after washing the conidia repeatedly. The germination-inhibiting substances were searched for in the acetone extract of potato-sucrose-agar (PSA) cultures of the fungus and five active compounds were isolated. Their structures were characterized spectroscopically. HPLC analysis indicated that one of the isolated compounds among these was exuded not only from mycelia but also from the conidia in water under crowded conditions. We suggest that these compounds control the conidial germination of the fungi.

Structures of Antafumicins A and B, Novel Antifungal Substances Produced by the Fungus Aspergillus niger NH-401

Novel antifungal substances, antafumicins A and B, were isolated from a culture of Aspergillus niger NH-401 and determined to be trans- and cis-4-(3-acetyl-2,6-dihydroxyphenyl)-2-methoxy-4- butanolide, respectively, by spectroscopic and single crystal X-ray analyses.

Pathogenicity-Related Compounds Produced by Blast Fungus

For over a hundred years, it has been discussed whether or not Pyricularia isolates on rice (Oryza sativa) and on crabgrass (Digitaria sanguinalis) belong to the same species, Pyricularia grisea (teleomorph, Magnaporthe grisea). We thought that pyrichalasin H, isolated from a Digitaria isolate, could be used as a marker of the chemotaxonomy of Pyricularia isolates. Pyrichalasin H was only detected in culture filtrates of Pyricularia isolates to infect Digitaria plants among 72 isolates from 20 species of gramineous plants. There was a correlation between pyrichalasin H production and the ability of Pyricularia isolates to infect Digitaria. Pre-treatment of leaf sheaths of crabgrass with pyrichalasin H led to penetration and colonization by nonhost isolates. Thus, we propose that pyrichalasin H may be responsible for the specific pathogenicity of Pyricularia isolates on the Digitaria genus. This result also supports the concept that isolates from rice and other cereals should be referred to as Magnaporthe oryzae and isolates from Digitaria shouldbe referred to as M. grisea. The blast fungus produces necrotic lesions on its original host plant. These lesions might be formed by phytotoxins of blast fungus. Some necrosis-inducing factors have been isolated from Pyricularia isolates. However, their toxins have not been compared to their quantities in cultures of Pyricularia isolates and their activity on host plants. We searched for the necrosis-inducing factor from a Triticum isolate pathogenic on wheat (Triticum aestivum). Pyriculol and epipyriculol were detected as the main necrosis-inducing factors.