THE USE OF MOLECULAR MARKERS TO STUDY SETOSPHAERIA-TURCICA RESISTANCE IN MAIZE

To facilitate understanding of the molecular basis of Htn1 resistance in maize to northern corn leaf blight, we mapped the Htn1 locus by restriction fragment length polymorphism (RFLP) analysis. Linkage with the Htn1 locus, using a backcross population, was initially detected with the RFLP probe UMC16, which hybridized to two loci: UMC16A on the long arm of chromosome three and the unmapped locus UMC16B. Independent assortment of Htn1 with UMC16A and linkage to UMC16B was verified with RFLP markers closely flanking UMC16A on the long arm of chromosome three. Information obtained from previous studies, detailing duplicate loci in maize, indicated that RFLP loci in the region around UMC16A are duplicated on the long arm of chromosome eight in the region of Idh1. RFLP loci mapping within this region on chromosome eight detected linkage with both Htn1 and UMC16B. Analysis of additional backcross progeny mapped the Htn1 locus 0.8 cM (centi-Morgans) distal to UMC117, near the recently reported location of the Ht2 locus. Segregation analysis of F-2 progeny from crosses of the inbred W22Htn1 with A619Ht2 confirmed the linkage of Htn1 with Ht1. RFLP analysis of susceptible F-2 progeny indicates that Htn1 and Ht2 are not allelic, and Ht2 maps are approximately 10 cM proximal to Htn1.