Nested association mapping (NAM) offers power to resolve complex, quantitative traits to their causal loci. The maize NAM population, consisting of 5,000 recombinant inbred lines (RILs) from 25 families representing the global diversity of maize, was evaluated for resistance to southern leaf blight (SLB) disease. Joint-linkage analysis identified 32 quantitative trait loci (QTLs) with predominantly small, additive effects on SLB resistance. Genome-wide association tests of maize HapMap SNPs were conducted by imputing founder SNP genotypes onto the NAM RILs. SNPs both within and outside of QTL intervals were associated with variation for SLB resistance. Many of these SNPs were within or near sequences homologous to genes previously shown to be involved in plant disease resistance. Limited linkage disequilibrium was observed around some SNPs associated with SLB resistance, indicating that the maize NAM population enables high-resolution mapping of some genome regions.

Maize inbred lines NC292 and NC330 were derived by repeated backcrossing of an elite source of southern leaf blight (SLB) resistance (NC250P) to the SLB-susceptible line B73, with selection for SLB resistance among and within backcross families at each generation. Consequently, while B73 is very SLB susceptible, its sister lines NC292 and NC330 are both SLB resistant. Previously, we identified the 12 introgressions from NC250P that differentiate NC292 and NC330 from B73. The goals of this study were to determine the effects of each introgression on resistance to SLB and to two other foliar fungal diseases of maize, northern leaf blight and gray leaf spot. This was achieved by generating and testing a set of near isogenic lines carry single or combinations of just two or three introgressions in a B73 background. Introgressions 3B, 6A, and 9B (bins 3.03-3.04, 6.01, and 9.02-9.03) all conferred significant levels of SLB resistance in the field. Introgression 6A was the only introgression that had a significant effect on juvenile plant resistance to SLB. Introgressions 6A and 9B conferred resistance to multiple diseases.

Facultative/winter six‐row malting barley is a distinct elite germplasm pool and a valuable resource that may prove useful in meeting the challenges of climate change. To preserve its diversity and make it accessible to the research and agricultural communities, the Oregon State University and University of Minnesota barley breeding programs are publicly releasing their winter/facultative six‐row malt advanced lines named the TCAP FAC‐WIN6 (MP‐1, NSL 512632 MAP), which also function as a genomewide association studies (GWAS) panel. The FAC‐WIN6 contains 296 lines—180 facultative and 116 winter—selected for disease resistance, malt quality, and general agronomic performance. To date, all lines have data for 6892 single nucleotide polymorphism (SNP) markers and phenotypic data from six experiments (representing 3 yr, eight locations), including traits such as malt quality, disease resistance, nitrogen use efficiency, and winter hardiness. The FAC‐WIN6 is one of 24 barley and wheat mapping panels and populations from the USDA‐ARS Triticeae Coordinated Agricultural Project (TCAP). As such, all of the TCAP FAC‐WIN6 genotypic and phenotypic data can be freely downloaded from the TCAP's online database, T3 (http://triticeaetoolbox.org/barley/). Preliminary GWAS have identified novel loci for wort β‐glucan, low temperature tolerance, and disease resistance. Given these results, the FAC‐WIN6 is a singular resource both for future winter six‐row barley breeding and for identifying and deploying genes for key barley traits in all backgrounds.

The fungal disease barley stripe rust (BSR, causal agent Puccinia striiformis f. sp. hordei) can greatly reduce yield and quality of malt barley (Hordeum vulgare L.), a valuable crop in the distilling and brewing industries. Yield losses of up to 70% have been reported. Resistant cultivars are the most sustainable defense against BSR, especially those cultivars with pyramids of quantitative disease resistance (QDR) genes. The Oregon State University (OSU) barley breeding program has selected for BSR resistance for decades and has released cultivars with BSR resistance. We wanted to determine the number and effect of the loci underlying that resistance, as well as whether it was conferred by QDR or race‐specific qualitative loci. To test these, we used BSR resistance quantitative trait loci (QTL) mapping via genomewide association studies (GWAS) in adult‐plant field trials (3 yr, one location) and race‐specific seedling greenhouse trials (five races). The FAC‐WIN6, a GWAS panel composed of 300 lines that represent the OSU and University of Minnesota facultative and winter six‐rowed malt barley breeding programs, was used in genotyping and phenotyping. The FAC‐WIN6 was developed as part of the USDA‐ARS Triticeae Coordinated Agricultural Project but was not developed specifically for BSR resistance. In total, we detected three race‐specific QTL in greenhouse trials (one of which was also significant in field trials) and 14 QTL significant in field trials only with 2.3 to 20.7% additive reduction in percentage disease severity. At least five QTL were considered novel. These results indicated that the OSU breeding program had both QDR and race‐specific loci for BSR resistance. We suspected that its BSR resistance distributions in the FAC‐WIN6 might align with the major population structure patterns in ways that would be difficult to account for with a GWAS model alone. Therefore, based on post hoc diagnostics, we report a qualitative “usability” level for each QTL.