Comparative Quantitative Trait Loci Mapping of Partial Resistance toPuccinia sorghiAcross Four Populations of European Flint Maize

We mapped and characterized quantitative trait loci (QTL) for partial resistance to Puccinia sorghi and investigated consistency across different European flint maize populations. Four independent populations, containing 280 F 3 lines (A×B I ), 120 F 5 lines (A×B II ), 131 F 4 lines (A×C), and 133 F 4 lines (C×D) were produced from four European elite flint inbreds (A, B, C, and D) and genotyped at 89, 151, 104, and 122 restriction fragment length polymorphism marker loci, respectively. All F n lines were evaluated in field trials with two replications in three or five (A×B I ) environments. Genotypic variance was highly significant for rust ratings in all populations, and heritabilities exceeded 0.64. Between 4 and 13 QTL were detected in individual populations using composite interval mapping, explaining between 33 and 71% of the phenotypic variance. Twenty QTL were distributed over all ten chromosomes, without preference to chromosomes 3, 4, 6, and 10, which harbor qualitatively acting Rp loci. In most cases, gene action was additive or partially dominant. Four pairs of QTL displayed significant digenic epistatic interactions, and QTL-environment interactions were observed frequently. Approximately half of the QTL were consistent between A×B I and A×B II or A×C and C×D; fewer were consistent between A×B I and A×C or C×D. In European flint maize germ plasm, conventional selection for partial rust resistance seems to be more promising than marker-assisted selection.