VIEW ARTICLE

Resistance

Resistance of Maize to Anthracnose: Changes in Host Phenols and Pigments. R. Hammerschmidt, Graduate Research Assistant, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907; R. L. Nicholson, Assistant Professor, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. Phytopathology 67:251-258. Accepted for publication 8 September 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-251.

The resistance of corn to Colletotrichum graminicola was studied with respect to phenol metabolism and lesion development in susceptible (Mo940), resistant (H91), and hypersensitive-resistant (33-16) inbreds. From chlorophyll content and visual observations, it was impossible to distinguish susceptible and hypersensitive-resistant responses prior to 42 hr after inoculation. These host responses could, however, be differentiated after 62 hr by chlorophyll regeneration in the hypersensitive host-pathogen combination. Host responses could also be differentiated by changes in phenol content. Total phenol content (ethyl acetate- and water-soluble phenols) of all three inbreds increased with time after inoculation. However, phenol content in the resistant and hypersensitive-resistant inbreds increased 48 hr prior to the increase detected in the susceptible inbred. At 42 hr after inoculation the ethyl acetate-soluble phenols in the resistant and hypersensitive-resistant inbreds had increased by approximately 74 and 110%, respectively, as compared to no detectable increase in those phenols in the susceptible inbred. Three phenolic compounds, M1, M2, and M3, accumulated in each of the inbreds after inoculation. These compounds accumulated earlier in the resistant and hypersensitive-resistant interactions than in the susceptible interaction. Compounds M1 and M2 were suggested to be flavonoids of the flavone group based on tests with chromogenic reagents, separation by thin-layer chromatography, and ultraviolet spectral analysis. Both M1 and M2 were fungitoxic to C. graminicola in spore germination and chromatographic bioassays. Compound M3, which was not distinguishable from caffeic acid, was not inhibitory to C. graminicola at the concentrations tested. Anthocyanin pigments accumulated in the resistant and hypersensitive-resistant hosts, but not in the susceptible host. Anthocyanins accumulated after the initial changes in total phenol content and after the increase in M1, M2, and M3. A role for phenolic metabolism in resistance of corn to C. graminicola is suggested, based on a correlation of lesion restriction with the accumulation of total phenolic compounds (compounds M1, M2, and M3) and the appearance of anthocyanins.