News and Views
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| Spores
(conidia) of Pyricularia grisea. (Courtesy P.J. Landschoot)  |
Young
blast lesions caused by Pyricularia grisea. (Courtesy APS) |
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| Mature
blast lesions showing necrotic (dead) borders. (Courtesy APS) |
Panicle
with neck blast. (Courtesy APS) |
Disease: Rice Blast
Pathogen: Magnaporthe grisea
Host: Rice, Oryza sativa
Blast is one of the most important diseases of rice worldwide, and it occurs in nearly every region in which rice is grown. Blast is more severe in temperate regions of the world, at higher elevations in the tropics, and in the upland areas where rice is rainfed (not grown in paddies).
Initially, the pathogen produces lesions on leaves when spores germinate and infect leaf tissue (figure 1). The color of these lesions can vary with environment and host resistance. The first lesions are often whitish to gray-green in color with dark green margins (figure 2), but they rapidly expand to the more characteristic diamond-shaped lesion (figure 3). Although leaf infections are serious, the most destructive phase of the disease results from the infection of the panicle where the rice forms (figure 4). The fungus sporulates heavily on lesions, a characteristic that contributes to the severity of epidemics.
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