Characterization and fine-mapping of a resistance locus for northern leaf blight in maize bin 8.06.

As part of a larger effort to capture diverse alleles at a set of loci associated with disease resistance in maize, DK888, a hybrid known to possess resistance to multiple diseases, was used as a donor in constructing near-isogenic lines (NILs). A NIL pair contrasting for resistance to northern leaf blight (NLB), caused by Setosphaeria turcica, was identified and associated with bin 8.06. This region of the maize genome had been associated in previous studies with both qualitative and quantitative resistance to NLB. In addition, bins 8.05-8.06 had been associated with quantitative resistance to several other diseases, as well as resistance gene analogs and defense response gene homologs. To test the hypothesis that the DK888 allele at bin 8.06 (designated qNLB8.06 ( DK888 )) conditions the broad-spectrum quantitative resistance characteristic of the donor, the NILs were evaluated with a range of maize pathogens and different races of S. turcica. The results revealed that qNLB8.06 (DK888) confers race-specific resistance exclusively to NLB. Allelism analysis suggested that qNLB8.06 (DK888) is identical, allelic, or closely linked and functionally related to Ht2. The resistance conditioned by qNLB8.06 was incompletely dominant and varied in effectiveness depending upon allele and/or genetic background. High-resolution breakpoint analysis, using approximately 2,800 individuals in F(9)/F(10) heterogeneous inbred families and 98 F(10)/F(11) fixed lines carrying various recombinant events, delimited qNLB8.06 ( DK888 ) to a region of approximately 0.46 Mb, spanning 143.92-144.38 Mb on the B73 physical map. Three compelling candidate genes were identified in this region. Isolation of the gene(s) will contribute to better understanding of this complex locus.