Soybean [Glycine max (L.) Merr.] yield, when regressed on water needed to replenish 0 to 100% seasonal evapotranspiration (ET), generates an estimate of season‐specific water‐use efficiency (WUE). The impact of unpredictable water deficits might be lessened if high‐yielding genotypes had a smaller beta. Our objective was to determine the genetic basis of beta and carbon isotope discrimination (CID), a theorized indicator of transpiration efficiency (TE). A ‘Minsoy’ × ‘Noir 1’ population of 236 recombinant inbred lines (RILs), genotyped at 665 loci, was evaluated in six water treatments (100, 80, 60, 40, 20, and 0% ET) for 2 yr. Water stress was mild in 1994, but high temperatures and no rainfall in 1995 led to a drought so severe that the 100% ET treatment required 41 cm of irrigation. The 1995 yield‐to‐water regression was highly linear (28 kg ha−1 cm−1). Genotype × water (G × W) interaction was due to genotypic heterogeneity in beta The CID vs. beta correlation was low (r = 0.26), so selection for better leaf TE may not improve crop WUE. Selection of low beta (less sensitivity to drought) will be difficult, given the yield beta vs. yield correlation (r = 0.71). The major quantitative trait loci (QTL) for yield beta, yield, and CID were coincident with maturity and/or determinancy QTLs, except for a CID QTL in linkage group U09‐C2, but it had no effect on beta Genetic improvement of soybean yield performance under drought would be better achieved by coupling a high‐yield grand mean with a high‐ (not low‐) yield beta

are homozygous and their genotypes can be reproduced by different research groups for repeated experiments Molecular markers provide a rapid approach to breeding for dein a variety of environments (Mather and Jinks, 1977). sired agronomic traits. To use them, it is necessary to determine the linkage between quantitative trait loci (QTLs) and such markers. The

Many agronomic traits of interest to plant breeders are quantitative. Recombinant inbred (RI) lines are particularly useful in genetic mapping studies of quantitative traits. A recombinant inbred population was derived from the Glycine max (L.) Merr. parents ‘Minsoy’ and ‘Noir 1’. This soybean population was used to investigate the genetic basis of several agronomic traits: days to flower (Rl), days to maturity (R8), reproductive period (RS‐R1), plant height, lodging score, height divided by lodging (the ability of tall plants to stand upright), seed protein content, seed oil content, seed size, yield, seed number, yield divided by height (the yield from short plants), leaf width, leaf length, and leaf area. In this RI population, transgressive segregation was observed for all of these traits. As expected, height and lodging were correlated, as were height and maturity; height and maturity with yield; and leaf length and width with leaf area. Height divided by lodging and yield divided by height showed little correlation with other traits, indicating that these traits measured new plant phenotypes. A genetic map was constructed for this population, with restriction fragment length polymorphism markers, simple sequence repeat markers and classical markers. Approximately 2000 cM of linkage was defined. The data were used to identify quantitative trait loci (QTLs) by linking quantitative phenotypes to qualitative genetic markers. for many traits, a few QTLs accounted for a large proportion of the variation observed. QTLs for most of the traits were associated with three linkage groups, often with the same genetic locus within the linkage group. At the level of resolution of the genetic map for this population, it was not possible to determine whether these QTLs have pleiotrophic effects or are clusters of separate, tightly linked genes. The data suggest that separation of QTLs for different traits (such as maturity or lodging and yield) may be difficult, but that this RI population will be useful in resolving questions concerning marker assisted selection of quantitative traits.

Soybean improvement via plant breeding has been critical for the success of the crop. The objective of this study was to quantify genetic change in yield and other traits that occurred during the past 80 yr of North American soybean breeding in Maturity Groups (MGs) II, III, and IV. Historic sets of 60 MG II, 59 MG III, and 49 MG IV soybean cultivars, released from 1923 to 2008, were evaluated in field trials conducted in 17 U.S. states and one Canadian province during 2010 to 2011. Averaged over 27 MG II and MG IV and 26 MG III site-years of data, the estimated rates of yield improvement during the 80 yr were 23 kg ha -1 yr -1 for MGs II and III, and 20 kg ha -1 yr -1 for MG IV cultivars. However, a two-segment linear regression model provided a better fit to the data and indicated that the average current rate of genetic yield gain across MGs is 29 kg ha -1 yr -1 . Modern cultivars yielded more than old cultivars in all environments, but particularly in high-yielding environments. New cultivars in the historic sets used in this study are shorter in height, mature later, lodge less, and have seeds with less protein and greater oil concentration. Given that on-farm soybean yields in the United States are also increasing at a rate of 29 kg ha -1 yr -1 , it can be inferred that continual release of greater-yielding cultivars has been a substantive driver of the U.S. onfarm realized yield increases.

Soybean [Glycine max (L.) Merr.] seeds contain high levels of protein and oil useful for human consumption. Increasing emphasis in breeding programs to produce soybeans with specific protein or oil content for specialty markets demands that more efficient manipulation of these traits be achieved. The objective of this study was to evaluate eight different soybean populations from the midwestern USA for genetic markers linked to seed protein and oil content. The populations were derived from the breeding programs at the Univ. of Minnesota, the Univ. of Nebraska, and Purdue Univ.‐USDA‐ARS. Each population consisted of between 69 and 100 individuals and was mapped with 21 to 85 restriction fragment length polymorphism markers. The F2‐derived populations were grown in field tests in 1992, 1993, and 1994 in the state in which they originated. Single factor analysis of variance was used to detect significant associations between markers and traits. Environmentally stable and environmentally sensitive quantitative trait loci (QTL) were identified for both protein and oil contents in all eight populations. The identified QTL were sensitive to both environment and genetic background although some common QTL were identified in multiple populations across several years. The results show that a number of QTL affect these traits and that markers could potentially be used in breeding programs designed to alter the seed protein and oil content.

Mutagenized populations have become indispensable resources for introducing variation and studying gene function in plant genomics research. In this study, fast neutron (FN) radiation was used to induce deletion mutations in the soybean (Glycine max) genome. Approximately 120,000 soybean seeds were exposed to FN radiation doses of up to 32 Gray units to develop over 23,000 independent M2 lines. Here, we demonstrate the utility of this population for phenotypic screening and associated genomic characterization of striking and agronomically important traits. Plant variation was cataloged for seed composition, maturity, morphology, pigmentation, and nodulation traits. Mutants that showed significant increases or decreases in seed protein and oil content across multiple generations and environments were identified. The application of comparative genomic hybridization (CGH) to lesion-induced mutants for deletion mapping was validated on a midoleate x-ray mutant, M23, with a known FAD2-1A (for fatty acid desaturase) gene deletion. Using CGH, a subset of mutants was characterized, revealing deletion regions and candidate genes associated with phenotypes of interest. Exome resequencing and sequencing of PCR products confirmed FN-induced deletions detected by CGH. Beyond characterization of soybean FN mutants, this study demonstrates the utility of CGH, exome sequence capture, and next-generation sequencing approaches for analyses of mutant plant genomes. We present this FN mutant soybean population as a valuable public resource for future genetic screens and functional genomics research.

We identified QTL associated with protein and amino acids in a soybean mapping population that was grown in five environments. These QTL could be used in MAS to improve these traits. Soybean, rather than nitrogen-containing forages, is the primary source of quality protein in feed formulations for domestic swine, poultry, and dairy industries. As a sole dietary source of protein, soybean is deficient in the amino acids lysine (Lys), threonine (Thr), methionine (Met), and cysteine (Cys). Increasing these amino acids would benefit the feed industry. The objective of the present study was to identify quantitative trait loci (QTL) associated with crude protein (cp) and amino acids in the 'Benning' × 'Danbaekkong' population. The population was grown in five southern USA environments. Amino acid concentrations as a fraction of cp (Lys/cp, Thr/cp, Met/cp, Cys/cp, and Met + Cys/cp) were determined by near-infrared reflectance spectroscopy. Four QTL associated with the variation in crude protein were detected on chromosomes (Chr) 14, 15, 17, and 20, of which, a QTL on Chr 20 explained 55 % of the phenotypic variation. In the same chromosomal region, QTL for Lys/cp, Thr/cp, Met/cp, Cys/cp and Met + Cys/cp were detected. At these QTL, the Danbaekkong allele resulted in reduced levels of these amino acids and increased protein concentration. Two additional QTL for Lys/cp were detected on Chr 08 and 20, and three QTL for Thr/cp on Chr 01, 09, and 17. Three QTL were identified on Chr 06, 09 and 10 for Met/cp, and one QTL was found for Cys/cp on Chr 10. The study provides information concerning the relationship between crude protein and levels of essential amino acids and may allow for the improvement of these traits in soybean using marker-assisted selection.

The economic and environmental costs of weed management in soybean (Glycine max [L.] Merr.) have led to interest in developing weed suppressive soybean varieties to enhance traditional herbicide and tillage‐based approaches. We evaluated 104 inbred progeny from three crosses among elite soybean lines to determine optimal selection criteria for weed suppressive ability (WSA). We grew the lines in 1996 and 1997 at Becker, MN, an irrigated sandy site, and Rosemount, MN, a rainfed silt loam site, in a split‐plot, with and without white mustard (Brassica hirta Moench). We measured soybean height 7 wk after emergence (WAE), light interception 5 and 7 WAE, specific leaf area 7 WAE, and date of full bloom. We harvested aboveground mustard biomass 8 WAE and calculated each soybean line's WSA as the difference between mustard biomass when grown in competition with that line and the overall mean mustard biomass. We estimated genetic correlations between soybean morphological traits, WSA, and the agronomic traits lodging, maturity date, and yield. Soybean early height's heritability true(h2=0.64true) and genetic correlation with WSA (r = 0.81) made it an ideal selection criterion. Indirect selection on height increased predicted selection efficiency by 70% relative to direct selection on mustard dry weight. Restricted index selection combining information on early height and lodging or yield eliminated undesirable correlated responses of lodging and yield while maintaining genetic gain for early height and WSA. Nevertheless, continuing rapid gains in agronomic performance while incorporating WSA may be difficult.