A major QTL ( qRtsc8 - 1 ) conditioning resistance to tar spot complex of maize and occurring at a frequency of 3.5 % across 890 maize inbred lines. Tar spot complex (TSC) is a highly destructive disease of maize found in some countries in America. Identification of TSC resistant germplasm and elucidating the genetic mechanism of resistance is crucial for the use of host resistance to manage this disease. We evaluated 890 elite maize inbred lines in multiple environments and used genome wide association analysis (GWAS) with genotypic data from Illumina MaizeSNP50 BeadChip containing 56 K SNPs to dissect the genetics of TSC resistance. GWAS results were validated through linkage analysis in three bi-parental populations derived from different resistant and susceptible parents. Through GWAS, three TSC resistance loci were identified on chromosome 2, 7 and 8 (-log10 (p)> 5.99). A major quantitative resistance locus (QTL) designated qRtsc8-1, was detected on maize chromosome bin 8.03. qRtsc8-1, was confirmed in three independent bi-parental populations and it accounted for 18-43 % of the observed phenotypic variation for TSC. A rare haplotype within the qRtsc8-1 region, occurring at a frequency of 3.5 % increased TSC resistance by 14 %. Candidate gene analysis revealed that a leucine-rich repeat receptor-like protein (LRR-RLKs) gene family maybe the candidate gene for qRtsc8-1. Identification and localization of a major locus conditioning TSC resistance provides the foundation for fine mapping qRtsc8-1 and developing functional markers for improving TSC resistance in maize breeding programs. To the best of our knowledge, this is the first report of a major QTL for TSC resistance.

BackgroundNorthern corn leaf blight (NCLB) caused by Exserohilum turcicum is a destructive disease in maize. Using host resistance to minimize the detrimental effects of NCLB on maize productivity is the most cost-effective and appealing disease management strategy. However, this requires the identification and use of stable resistance genes that are effective across different environments.ResultsWe evaluated a diverse maize population comprised of 999 inbred lines across different environments for resistance to NCLB. To identify genomic regions associated with NCLB resistance in maize, a genome-wide association analysis was conducted using 56,110 single-nucleotide polymorphism markers. Single-marker and haplotype-based associations, as well as Anderson-Darling tests, identified alleles significantly associated with NCLB resistance. The single-marker and haplotype-based association mappings identified twelve and ten loci (genes), respectively, that were significantly associated with resistance to NCLB. Additionally, by dividing the population into three subgroups and performing Anderson-Darling tests, eighty one genes were detected, and twelve of them were related to plant defense. Identical defense genes were identified using the three analyses.ConclusionAn association panel including 999 diverse lines was evaluated for resistance to NCLB in multiple environments, and a large number of resistant lines were identified and can be used as reliable resistance resource in maize breeding program. Genome-wide association study reveals that NCLB resistance is a complex trait which is under the control of many minor genes with relatively low effects. Pyramiding these genes in the same background is likely to result in stable resistance to NCLB.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0589-z) contains supplementary material, which is available to authorized users.

been removed from the soil by leaching or via harvested crops (Granados et al., 1993). Acidic soils, therefore, Soil acidity reduces maize (Zea mays L.) yields by up to 70% on generally have a low pH, contain toxic levels of Al and 8 million hectares in developing countries. Several breeding programs have produced populations better adapted to these conditions. TheMn, and are deficient in Ca, Mg, P, K, and Mo. These objectives of this study were to evaluate these populations for both characteristics limit the fertility of acid soils and inhibit per se cultivation and the development of new breeding germplasm. root development, leading to low water and nutrient up-To do so, we generated a diallel cross design, which included six acid take and low maize yields (Duque-Vargas et al., 1994). soil-tolerant and five susceptible populations with high yield potential Soil amendments (the application of lime and fertilizor tolerance to other stresses. Populations and crosses were evaluated ers) have been used to bring acid soils under agricultural in five environments, on acidic Al-toxic soils and in comparable limed production. However, such solutions may not be envisoils in Guadeloupe, Cameroon, and Colombia. Soil acidity decreased ronmentally friendly, have only a temporary effect, and grain yield by 46 to 73%, depending on the location and year. Signifiare too expensive for poor farmers in developing councant genotype ϫ soil condition interactions were observed for grain tries (The et al., 2001). The use of acid soil-tolerant maize yield. Mid-parent heterosis for yield was significantly higher in acid soils (32%) than in nonacid soils (20%). This suggests that the develop-cultivars provides an environmentally friendly, inexpenment of variety crosses between acid soil-tolerant populations could sive, and permanent solution, contributing to sustainbe used to increase maize yields in acid-soil cropping systems. The able crop production on acid soils (Granados et al., observed high general combining ability (GCA) for yield variation of 1993). the crosses in acid soil and its close relationship to per se performance Considerable genetic variation in acid-soil tolerance suggest that parental populations of variety crosses could be efficiently has been reported in maize. Early studies demonstrated screened on the basis of per se performance in acid soil.

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