Pathogen survival and host resistance in the eyespot disease of maize caused by Kabatiella zeae Narita and Hiratsuka
Twenty-two inbreds and the crosses of 3 tester lines (MS153, W64A B84) with 14 inbreds were artificially inoculated with K. zeae. Data on proportion of disease (X) for each genotype were collected periodically, transformed by the Gompertz equation (-1n - 1n(X)), and regressed on time. The k values (regression coefficients) differed statistically among genotypes. Genotypes with the largest k values had the highest levels of disease. A regression analysis of the k values on days to tasseling yielded negative regression coefficients that were significant for the inbreds and for each group of crosses with the 3 testers. Early maturing genotypes were more susceptible, yet it was clear that factors other than maturity conditioned susceptibility. The reaction of the F(,1) crosses to the disease varied according to the susceptibility of the tester lines regardless of maturity;The inbreds and hybrids were quantitatively inoculated in the greenhouse and the number of lesions/plant recorded. The greenhouse data did not correlate with the k values obtained for the genotypes in the field;The survival of K. zeae in maize residues was studied in a no-till field where eyespot inoculum was present. The residues were removed at different intervals. The disease appeared later and at lower severity in plots where infested residues were removed before planting or early in the season than in plots where residues were present on the soil the full season. Residues collected from the no-till plots and spread in a disease-free field initiated eyespot lesions only when collected early in the season (May-June). In another experiment, the disease appeared later and the initial level was lower in plots that had the lowest amount of disease the previous season. In some experiments, the early season differences in disease severity among treatments persisted until harvest and, in others, these differences disappeared as the season progressed;Infested leaf residues and laboratory cultured stromatic hyphae of K. zeae rapidly lost their potential for conidial production after several consecutive cycles of wetting and drying in the laboratory. The sporulation potential decreased to about 0.01% of the original inoculum with five cycles of wetting and drying.