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Ecology and Epidemiology

Effects of Temperature and Host Maturity on Lesion Development of Colletotrichum graminicola on Corn. K. J. Leonard, Plant Pathologist, Southern Region, Agricultural Research Service, United States Department of Agriculture, North Carolina State University, Raleigh, North Carolina 27607; D. L. Thompson, Research Agronomist, Southern Region, Agricultural Research Service, United States Department of Agriculture, North Carolina State University, Raleigh, North Carolina 27607. Phytopathology 66:635-639. Accepted for publication 10 November 1975. DOI: 10.1094/Phyto-66-635.

Corn plants of 12 genotypes were inoculated with Colletotrichum graminicola in the four- to five-leaf stage and grown at 20, 24, 26, 28, 30, and 32 C in controlled environment rooms. The optimum temperature for lesion elongation was 30 C. Lesion elongation was linear with time. Significant differences in susceptibility were noted among the 12 genotypes. Plants of corn cultivar Gaspe Flint were grown in a controlled environment room and inoculated at 2, 3, 4, 5, 6, 7, and 8 weeks after planting. Plants shed pollen at 33 days and reached physiological maturity at 58 days. After 9 to 10 weeks, most plants were senescent. Plants inoculated at 5 and 6 weeks after planting developed fewer lesions per square centimeter of leaf area, and the lesions were smaller than those on plants inoculated either earlier or later in their development. The greatest numbers of lesions per square centimeter occurred on lower leaves of young plants and on the top leaves of plants 7 or 8 weeks old at inoculation. The relationship between lesion size and leaf position on the plants was nearly linear, with the largest lesions on the lowest leaves. These results suggest that the pattern of early summer leaf infections and late summer leaf and stalk infections in the field is related to changes in host susceptibility. Little or no disease was found in the field in midsummer.