Resistance of Maize to Anthracnose: Changes in Host Phenols and Pigments

HAMMERSCHMIDT, R. , and R. L. NICHOLSON. 1977. Resistance of maize to anthracnose: changes in host phenols and pigments. Phytopathology 67: 251-258. The resistance of corn to Colletotrichum graminicola was compounds, Ml, M2, and M3, accumulated in each of the studied with respect to phenol metabolism and lesion inbreds after inoculation. These compounds accumulated development in susceptible (Mo940), resistant (H91), and earlier in the resistant and hypersensitive-resistant hypersensitive-resistant (33-16) inbreds. From chlorophyll interactions than in the susceptible interaction. Compounds content and visual observations, it was impossible to M l and M2 were suggested to be flavonoids of the flavone distinguish susceptible and hypersensitive-resistant group based on tests with chromogenic reagents, separation responses prior to 42 hr after inoculation. These host by thin-layer chromatography, and ultraviolet spectral responses could, however, be differentiated after 62 hr by analysis. Both M I and M2 were fungitoxic to C. graminicola chlorophyll regeneration in the hypersensitive host-pathogen in spore germination and chromatographic bioassays. combination. Host responses could also be differentiated by Compound M3, which was not distinguishable from caffeic changes in phenol content. Total phenol content (ethyl acid, was not inhibitory to C. graminicola at the acetateand water-soluble phenols) of all three inbreds concentrations tested. Anthocyanin pigments accumulated increased with time after inoculation. However, phenol in the resistant and hypersensitive-resistant hosts, but not in content in the resistant and hypersensitive-resistant inbreds the susceptible host. Anthocyanins accumulated after the increased 48 hr prior to the increase detected in the initial changes in total phenol content and after the increase susceptible inbred. At 42 hr after inoculation the ethyl in Ml, M2, and M3. A role for phenolic metabolism in acetate-soluble phenols in the resistant and hypersensitiveresistance of corn to C. graminicola is suggested, based on a resistant inbreds had increased by approximately 74 and correlation of lesion restriction with the accumulation of 110%, respectively, as compared to no detectable increase in total phenolic compounds (compounds M l, M2, and M3) those phenols in the susceptible inbred. Three phenolic and the appearance of anthocyanins. Phenolic compounds accumulate in numerous plant corn lines deficient in hydroxamic acids, but possessing species following infection with plant pathogens (13, 14). monogenic resistance to H. turcicum (7). The nature of' Many of these compounds, or their oxidation products, the inhibitory factor(s) was not elucidated. Based on are toxic to pathogenic and nonpathogenic fungi and cross-protection studies, phytoalexin production has bacteria and have been considered to be factors in disease been suggested to account for resistance of corn to resistance. Biochemical resistance of corn has been Puccinia graminis (15), but no specific phenolic attributed primarily to the presence of cyclic phytoalexins have been identified or shown to hydroxamic acids (7, 9, 18). The level of cyclic accumulate in corn in response to infection. hydroxamates present prior to infection has been Hammerschmidt and Nicholson (10) demonstrated correlated with the degree of resistance to that the size of anthracnose lesions on lines of corn Helminthosporium turcicum (8). It is doubtful, however, resistant and hypersensitive-resistant to Colletotrichum that hydroxamates are primary resistance factors in corn graminicola were smaller when inoculated plants were (7, 8). Lim et al. demonstrated the presence of two grown under high light intensity. An accumulation of phenolic compounds in leaf diffusates (17) and water anthocyanins in the tissue surrounding lesions was extracts (16) of corn leaves 3-12 days after inoculation associated consistently with decreased lesion size. The with H. turcicum. Both compounds inhibited the accumulation of anthocyanins, which are flavonoid germination of spores of H. turcicum. Similarly, after glycosides, and the associated decrease in lesion size infection with H. turcicum, an inhibitor(s) of spore suggested that phenolic metabolism was involved in germination was demonstrated in leaf diffusates from resistance. In this study, we have investigated the role of phenolic metabolism in the resistance of corn (Zea mays L.) to Colletotrichum graminicola (Ces.) Wils. and have Copyright © 1977 The American Phytopathological Society, 3340 demonstrated the accumulation of specific phenols Pilot Knob Road, St. Paul, MN 55121. All rights reserved, associated with differential host responses to infection.