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Influence of Light on Maize Anthracnose in the Greenhouse. R. A. Schall, Plant pathologist (APHIS, USDA), Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907; R. L. Nicholson(2), and H. L. Warren(3). (2)(3)Associate professor, and research plant pathologist (SEA, USDA), Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. Phytopathology 70:1023-1026. Accepted for publication 25 April 1980. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1980. DOI: 10.1094/Phyto-70-1023.

When maize seedlings were inoculated in the greenhouse with Colletotrichum graminicola and incubated in the dark for 18 hr, the percentage of leaf tissue affected was influenced by light. Solar radiation was measured over an 8-day period from 2 days before the day of inoculation through 6 days after inoculation. Leaves of seedlings exposed to relatively low levels of solar radiation (1,234 gm cal/cm2) exhibited a significantly greater percentage of lesion coverage than did those of seedlings exposed to higher levels of light (2,530 to 3,361 gm cal/cm2). Among the 22 corn cultivars studied, lesion coverage under low light intensity ranged from 42.2 to 97.5% whereas under conditions of high light intensity, lesion coverage ranged from 0.2 to 57.2%. When seedlings were incubated in the dark for 42 hr following inoculation, the lesion coverage ranged from 53.2 to 100% regardless of the subsequent amount of solar radiation the plants received. Thus, the critical period for illumination was during the day after inoculation. The data demonstrate that high disease ratings may be obtained when light is limiting, such as during periods of extensive cloud cover. Though lesion coverage was variable, the host reaction type did not change under the variable light conditions. Evalution of plants for resistance should be done on the basis of host reaction type as well as extent of lesion coverage.

Additional keywords: Zea mays, corn hybrids, resistance, phenols.