Pathogenicity-Related Compounds Produced by Blast Fungus

Abstract

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.