Effect of Illuminance on the Resistance of Inbred Lines of Corn to Isolates ofColletotrichum graminicola

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Abstract
Three-week-old plants of 6 inbred lines of corn were inoculated in all combinations with 4 isolates of C. graminicola. From 1 wk before to 1 wk after inoculation the plants were grown at day/night temperatures of 30/26.degree. C and daytime illuminances of 455, 228 or 114 hlx. Lesion length, lesions per square centimeter, and sporulation per square centimeter decreased with increasing illuminance. Sporulation per lesion was highest at 228 hlx, slightly lower at 114 hlx, and lowest at 455 hlx. Isolate .times. line interaction effects were significant at P = 0.11, P = 0.10, and P = 0.07 for lesions per square centimeter, sporulation per lesion and sporulation per square centimeter, respectively, when analyzed over all 3 illuminance treatments. When data for each illuminance level in each of the 2 trials were analyzed separately, the isolate .times. line interaction was significant at P < 0.05 for one of 6 analyses for lesion length and sporulation per square centimeter. The levels of specific resistance present in the lines were estimated by three methods and the consistency of the estimates were compared. Estimates of specificity differed for different components of resistance.