Deciphering the genetic architecture of multi-foliar disease resistance in maize

Northern leaf blight (NLB) caused by Exserohilum turcicum and southern leaf blight (SLB) caused by Cochliobolus heterostrophus are devastating foliar diseases of maize. Although many quantitative trait loci (QTL) associated with NLB and SLB resistance have been identified, only a few have been validated and fine-mapped. Here, a recombinant inbred line (RIL) population consisting of 209 F_6:7 families was generated from a cross between the resistant line KB020 and the susceptible line PH4CV. Both the parental lines and all RILs were evaluated for NLB and SLB resistance in three environments and genotyped using Maize6H-60K single nucleotide polymorphism (SNP) array chip. Initial linkage mapping revealed 18 and 15 QTL for resistance to NLB and SLB, respectively. QTL for resistance to both NLB and SLB were co-localized in bins 2.06, 3.06, 4.05, 5.07 and 6.07. Two NLB QTL (qNLB3-1 and qNLB10-1) and four SLB QTL (qSLB3-2, qSLB4-1, qSLB3-5 and qSLB8-1) were successfully validated in field trials using near-isogenic lines (NILs) developed from heterogeneous inbred families (HIFs). qNLB3-1 and qSLB4-1 were further delimited to intervals of ~5 Mb and ~4.53 Mb, respectively. This study provides valuable insights into the genetic basis of NLB and SLB resistance and offers new resources for marker-assisted breeding for resistant maize varieties.