CHARACTERIZATION OF RACE-NONSPECIFIC RESISTANCE TO EXSEROHILUM-TURCICUM RACE-0 AND RACE-1 IN MAIZE OHS10 S-1 PROGENIES

Three field studies were conducted in 1990 and 1991 to characterize the type and level of resistance of 149 OhS10 selfed progenies to races 1 (tested in Ohio) and 0 (tested in Uganda) of Exserohilum turcicum, causal agent of northern leaf blight (NLB). Maize plants were inoculated in a controlled fashion, and disease severity was assessed once late in the season using a 0-5 visual rating scale. Visual estimates of percent leaf area affected (PLAA) and counts of lesions were made four to six times following inoculation. Host responses to infection were also characterized by determining lesion size, apparent infection rate, and area under the disease progress curve (AUDPC) calculated from PLAA and lesion number. Progenies ranged in degree of resistance from susceptible to highly resistant. The top tenth percentile of progenies were selected for study based on the 0-5 rating scale. The relative ranking of resistance to both races, and characterization of their host responses, indicated that selected progenies displayed a high level of race-nonspecific resistance. The 14 most resistant progenies displayed fewer lesions, lower PLAA ratings, lower rating scores (0-5), lower AUDPC values, and lower apparent infection rates than did the resistant inbred check (Mo17). Lesion lengths on the resistant progenies did not differ from those on Mo17. Disease assessment methods were generally highly correlated with one another.