The effect of environmental factors and plant age on the infection of rice by the blast fungus, Piricularia oryzae

Kahn, R.P.; Libby, J.L.

Phytopathology 48(1): 25-30


ISSN/ISBN: 0031-949X
Accession: 025748606

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A quantitative bioassay was utilized to assess the effects of plant age and various environmental factors on the infection of Caloro and Zenith rice leaf blades by Piricularla oryzae. Infection occurred between 60 and 95° F in dew cabinets with 16-20 hours of dew exposure; the optimum was 80° or 85°. The minimal periods required to initiate infection under dew-cabinet conditions were 10 hours at 80°, 12 hours at 70", and 14 hours at 65°. The upper surfaces of leaf blades were twice as susceptible as the lower surfaces. With increasing age of plant, leaves, or portions of the leaf blade, there was progressive decrease in susceptibility to infection. On susceptible varieties, leaves older than 8-10 weeks were resistant. Leaves of susceptible plants grown on non-flooded soils were more susceptible to infection than were leaves of plants grown on flooded soil. Greenhouse-grown plants were more susceptible than field-grown plants of the same age.