The production of resistant soybean [Glycine max (L.) Merr.] cultivars is the most effective means for controlling losses from soybean cyst nematode (SCN) (Heterodera glycines Ichinohe). The major resistance gene in most SCN resistance sources is rhg1, which has been mapped as a quantitative trait locus onto linkage group G. Our objective was to determine whether the SCN resistance sources PI 437654 and PI 88788 have different functional alleles at rhg1 based on resistance phenotypes. Populations segregating for resistance alleles at rhg1 from both PI 88788 and PI 437654 and at Rhg4, a second SCN resistance gene from PI 437654, were developed. These populations were screened for resistance to the H. glycines inbred isolates PA3 (HG type 7) and TN14 (HG type 1.2.5.7) in the greenhouse and evaluated with molecular markers linked to both rhg1 and Rhg4. Each isolate test was repeated, and the evaluations were done on a single-plant and a line-mean basis in Test 1, and solely on a single-plant basis in Test 2. Across two tests with the TN14 isolate, plants with the PI 437654 allele for a marker linked to rhg1 had significantly (P<0.0001) less SCN reproduction than plants carrying the PI 88788 allele. A marker linked to Rhg4, however, was not significantly associated with resistance to TN14. Across two tests with the PA3 isolate, alleles of rhg1 from both sources gave a resistant reaction, although plants homozygous for the PI 88788 allele had significantly (P<0.05) greater resistance than plants with the PI 437654 allele. The marker allele from PI 437654 linked to Rhg4 was significantly (P<0.0005) associated with greater resistance than the PI 88788 allele in both PA3 tests, and resistance was dominant. There was a significant interaction between alleles at rhg1 and Rhg4 in both PA3 tests. These results suggest that PI 437654 and PI 88788 each have a different functional SCN resistance allele at or close to rhg1. These allelic differences have implications that breeders should consider before incorporation into cultivars.

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Bean (Phaseolus vulgaris L.) production is challenged by many limitations with drought being among the top causes of crop failure worldwide. In this study, we constructed three small‐red‐seeded bean recombinant inbred line (RIL) mapping populations (S48M, S94M, and S95M) with a common parent (‘Merlot’) and performed joint interval mapping analysis as a small nested association mapping (NAM) population for agronomic traits and performance under rainfed conditions in Michigan. The objective was to identify novel sources of improved performance and genomic regions associated with desirable traits under rainfed and water‐sufficient conditions in small‐red bean breeding materials adapted to temperate zones. A composite linkage map was constructed using single‐nucleotide polymorphism (SNP) markers from the three populations and resulted in an improved version of the individual linkage maps shown by a greater genome span covered in the composite map (909 cM). A number of quantitative trait loci (QTL) of different size effects were identified for seed yield (R2 = 15.4–30.7%), seed size (R2 = 16.4–20.2%), days to flowering (R2 = 12.4–36.1%), days to maturity (R2 = 16.2%), lodging score (R2 = 10.3–12.9%), and canopy height (R2 = 17%). Our study confirmed previously reported QTL on five chromosomes and identified a new QTL for canopy height on chromosome Pv10. The use of a composite map and QTL analysis under a NAM population structure increased our ability to detect small‐effect QTL that were segregating in at least two of the populations but would not have been detected using individual linkage maps.

L egumes in symbiosis with soil rhizobia are reported to fix 20 to 22 million Mg of nitrogen (N) each year in agricultural production systems (Herridge et al., 2008). Large differences exist in the proportion of atmospheric N 2 fixed by grain legume crops, and common (dry) bean (Phaseolus vulgaris L.) is among the lowest in symbiotic N fixation (SNF). For example, 75% of the total N in a faba bean (Vicia faba L.) plant was derived through SNF; 62 to 94% of N in soybean [Glycine max (L.) Merr.], pea (Pisum sativum L.), and lentil (Lens culinaris Medikus); 54 to 58% of N in cowpea [Vigna ungiculata (L.) Walp.], chickpea (Cicer arietanum L.), and pigeon pea [Cajanus cajan (L.) Millsp.]; and 39% of N in common bean (Dwivedi et al., 2015). The percentage of nitrogen derived from the atmosphere (Ndfa) fixed by dry bean is also quite variable depending on genotype and environmental conditions. Using the 15 N natural abundance method, Farid et al., (2016) reported an average 28% Ndfa in low-N environments. Pereira et al. (1989) also reported an average Ndfa of 21.6%, but cultivars ranged from 5.7% for the navy bean 'Sanilac' to 31.6% for the black bean landrace 'Puebla 152'. A weak relationship ABSTRACT Dry bean (Phaseolus vulgaris L.) acquires nitrogen (N) from the atmosphere through symbiotic N fixation (SNF) but is considered a poor N fixer. Diversity for SNF within dry bean germplasm is recognized, and regions of the genome associated with SNF traits have recently been identified. In the current study a mapping population of 122 recombinant inbred lines (rILs), derived from the cross of two black bean cultivars ('puebla 152' and 'Zorro') contrasting in SNF traits, was grown in the field in East Lansing, MI, and Isabela, puerto rico, and in the greenhouse under N-free conditions to evaluate for yield, nodule development, biomass growth, agronomic traits, and N fixation. The rIL population was also genotyped with single-nucleotide polymorphism (SNp) markers developed through the BeanCAp to construct a genetic map spanning 972 cM and containing 430 SNps. A total of 17 unique QTL associated with SNF traits were identified with most of them located in three large clusters on pv01 (4), pv06 (6), and pv08 (6). Many of the QTL associated with %N derived from atmosphere, N harvest index, and %N in biomass were also associated with candidate genes expressed in the nodules and roots. The majority of QTL associated with genes expressed in the root or nodule were derived from puebla 152, while QTL associated with genes with enhanced expression in stems and pods were associated with Zorro. The QTL described should serve as potential targets for improvement of SNF characteristics in commercial dry bean genotypes adapted to temperate zones.

‘Eldorado’ (Reg. No. CV‐302, PI 665012) pinto bean (Phaseolus vulgaris L.), which was developed by Michigan State University AgBioResearch, was released in 2012 as an upright, full‐season, disease‐resistant cultivar. Eldorado, tested as MSU breeding line P07863, was developed using the single‐seed‐descent breeding method to the F4 generation followed by pedigree selection for disease, agronomic, and quality traits. In 5 yr of field trials, Eldorado yielded 3364 kg ha−1, flowered in 42 d, and matured in 98 d. Plants averaged 53 cm in height, with a lodging‐resistance score of 1.9 and a seed size of 43 g 100 seed−1. Eldorado combines exceptional yield potential and erect architecture with full‐season maturity in the pinto seed type. Eldorado has resistance to lodging and high pod placement within the plant structure, making it suitable for direct harvest under narrow‐row production systems. The upright architecture also contributes to avoidance of white mold [caused by Sclerotinia sclerotiorum (Lib.) de Bary], a disease intensified by narrow‐row production systems. In irrigated trials designed to promote the development of white mold disease, Eldorado had 30% incidence over 5 yr compared with other pinto cultivars that had from 42 to 72% white mold incidence. Eldorado possesses resistance to specific races of rust, virus, and anthracnose. Eldorado has a large, mottled, dry‐bean seed that meets industry standards for packaging and canning quality in the pinto bean seed class.