Field evaluation of maize inbred lines for resistance to Exserohilum turcicum
South African Journal of Plant and Soil
Agricultural Research Council, Grain Crops Institute, Private Bag 1251, Potchefstroom, 2520, South Africa
Nine maize inbred lines with excellent grey leaf spot resistance and good combining ability were evaluated for their reaction to infection by Exserohilum turcicum. The lines were compared to a differential set consisting of Oh43 and B73 (susceptible controls) and OMZHt1B, Oh43Ht2, Oh43Ht3, B37HtN (containing resistant genes) in both growth chamber and field trials. All nine lines possessed seedling resistance to northern corn leaf blight (NCLB). Two field trials were planted over two growing seasons (2007/08 and 2008/09) as randomized complete block designs with three replicates. Trials were inoculated twice (at the 4-5 and 8-12 leaf stages) with NCLB and disease assessments made at growth stages R1, R2, R3, R4 and R5. Disease progress curves were created and total severity (yt), diseased plant severity (ydp) and AUDPC were determined for each replicate. Linearised forms of the exponential, logistic and Gompertz models were fitted to the disease-progress data and the best model selected for each trial. Rate of disease increase (r) and level of disease at the onset of the epidemic (y0; time=0) were obtained from which y0* (back-transformed from y0) were determined. Canonical variate analysis (CVA) indicated that yt, ydp, sAUDPC and y0* were responsible for 73.68% of the variation observed between the lines, with r explaining 15.44% of the variation. Ranking of lines were based on their yt, y dp, sAU-DPC and y0* performance. GLS resistant lines 185-2, 182-2, 72-2A and 182-1 demonstrated higher levels of resistance to NCLB than that of lines Oh43Ht1B, Oh43Ht2, Oh43Ht3 and B37HtN while 122-2, 578 and 72-3 showed higher levels of resistance than that of Oh43Ht2 and B37HtN.
canonical analysis; disease resistance; disease severity; fungal disease; growing season; logistics; maize; Cercospora; Setosphaeria turcica; Zea mays