Effect of Resistance Type on the Development of and Yield Losses Due to Northern Corn Leaf Blight

Abstract

The effect of resistant type on the development of northern leaf blight (NLB), caused by Exserohilum turcicum, was studied on three dent corn (Zea mays L.) hybrids: A619 x A632, B73 x Oh545 and Mo17 x B73. Two nearly isogenic versions of each hybrid were used, one version carrying the resistance gene Ht1 and the second carrying the corresponding allele for susceptibility, ht1. Plots were inoculated at one of five different times, corresponding to growth stages (GS) 2 through 6.

The level of polygenic resistance greatly influenced initial lesion number. Greater lesion numbers were observed on the Ht1 versions of the three hybrids compared to the ht1 versions. Analysis of area under the disease progress curve showed that the ht1 versions of the hybrids had greater disease development. Differences in percent stalk lodging were observed only among ht1 hybrids.

Significant differences in grain yields were observed in two of three years. The lower grain yields were associated with inoculations at the early GS. No significant yield losses occurred when the percent leaf area infected (LAI) was less than 10% at silking. Reductions in 500 kernel weights were observed for the hybrid A619 x A632. Critical point (CP) and area under the disease progress curve (AUDPC) models were evaluated using untransformed and transformed data. For A619 x A632, the best model was obtained using AUDPC (Y = 92.97-0.12(AUDPC), r('2) = 0.68). CP models using LAI at ratings 7, 9 and 11 gave relatively good fit (r('2) = 0.66).