Use of a Maize Advanced Intercross Line for Mapping of QTL for Northern Leaf Blight Resistance and Multiple Disease Resistance

Northern leaf blight [NLB; caused by Exserohilum turcicum (Pass) K.J. Leonard and E.G. Suggs] is an important fungal disease of maize (Zea mays L.) in the United States and worldwide. The IBM population, an advanced intercross recombinant inbred line population derived from a cross between the lines Mo17 and B73, was evaluated in three environments (Aurora, NY, in 2006 and 2007 and Clayton, NC in 2007) for two traits related to NLB resistance, weighted mean disease (WMD) and incubation period (IP), and for days to anthesis (DTA). Two WMD quantitative trait loci (QTL) in bins 2.00/2.01 and 4.08 were detected from the overall analysis; of these, only the QTL in bin 4.08 was detected in all three environments analyzed separately. Likewise, only one IP QTL, in bin 2.02, was detected in all three environments and from the overall analysis. Several environment-specific OTL for each trait were also detected. Several DTA QTL were detected with the strongest effect detected in bin 8.05. Correlations between disease resistance traits and days to anthesis were uniformly low. The results from this study were compared to those of previous studies that used the IBM population to identify OTL for two other maize foliar diseases, southern leaf blight (causal agent Cochliobolus heterostrophus (Drechs.) Drechs. [anamorph = Bipolaris maydis (Nisikado and Miyake) Shoemaker; synonym = Helminthosporium maydis (Nisikado and Miyake)]} and gray leaf spot [causal agent Cercospora zeae-maydis (Tehon and E.Y. Daniels)]. Although we did not find QTL conferring resistance to all three diseases, significant correlations between resistances to these diseases in the IBM population were identified, implying the existence of loci (and possibly genes) affecting resistance to all three diseases.