Complex quantitative traits of plants as measured on collections of genotypes across multiple environments are the outcome of processes that depend in intricate ways on genotype and environment simultaneously. For a better understanding of the genetic architecture of such traits as observed across environments, genotype-by-environment interaction should be modeled with statistical models that use explicit information on genotypes and environments. The modeling approach we propose explains genotype-by-environment interaction by differential quantitative trait locus (QTL) expression in relation to environmental variables. We analyzed grain yield and grain moisture for an experimental data set composed of 976 F 5 maize testcross progenies evaluated across 12 environments in the U.S. corn belt during 1994 and 1995. The strategy we used was based on mixed models and started with a phenotypic analysis of multienvironment data, modeling genotype-by-environment interactions and associated genetic correlations between environments, while taking into account intraenvironmental error structures. The phenotypic mixed models were then extended to QTL models via the incorporation of marker information as genotypic covariables. A majority of the detected QTL showed significant QTL-by-environment interactions (QEI). The QEI were further analyzed by including environmental covariates into the mixed model. Most QEI could be understood as differential QTL expression conditional on longitude or year, both consequences of temperature differences during critical stages of the growth.T HE incidence of genotype-by-environment interactions (GEI) for quantitative traits has important implications for any attempts to understand the genetic architecture of these traits by mapping quantitative trait loci (QTL) and also for the effectiveness of attempts to improve these traits by both conventional and markerassisted selection (MAS) breeding strategies. The literature on GEI and QTL-by-environment interactions (QEI) for quantitative traits in maize is ambiguous, with evidence in favor (Moreau et al. 2004) and against (Ledeaux et al. 2006) their importance. The diversity of the results for the importance of QEI for quantitative traits in crop plants observed in the literature strongly suggests that explicit testing for their presence, magnitude, and form is a critical step in any attempt to understand the genetic architecture of these traits. Further, theoretical considerations of the impact of different forms of QEI on the outcomes of MAS in plant breeding (Podlich et al. 2004;Cooper et al. 2002Cooper et al. , 2005Cooper et al. , 2006 motivate the development of methods for explicitly studying the importance of QEI as a component of the genetic architecture of quantitative traits.When QEI occurs and environmental covariables derived from geographical and weather information are available, QTL effects across environments can be tested for dependence on particular environmental covariables (Crossa et al. 1999;Malosetti et al. 2004;Varga...

Kinetically improved diacylglycerol acyltransferase (DGAT) variants were created to favorably alter carbon partitioning in soybean (Glycine max) seeds. Initially, variants of a type 1 DGAT from a high-oil, high-oleic acid plant seed, Corylus americana, were screened for high oil content in Saccharomyces cerevisiae. Nearly all DGAT variants examined from high-oil strains had increased affinity for oleoyl-CoA, with S 0.5 values decreased as much as 4.7-fold compared with the wild-type value of 0.94 mM. Improved soybean DGAT variants were then designed to include amino acid substitutions observed in promising C. americana DGAT variants. The expression of soybean and C. americana DGAT variants in soybean somatic embryos resulted in oil contents as high as 10% and 12%, respectively, compared with only 5% and 7.6% oil achieved by overexpressing the corresponding wildtype DGATs. The affinity for oleoyl-CoA correlated strongly with oil content. The soybean DGAT variant that gave the greatest oil increase contained 14 amino acid substitutions out of a total of 504 (97% sequence identity with native). Seed-preferred expression of this soybean DGAT1 variant increased oil content of soybean seeds by an average of 3% (16% relative increase) in highly replicated, single-location field trials. The DGAT transgenes significantly reduced the soluble carbohydrate content of mature seeds and increased the seed protein content of some events. This study demonstrated that engineering of the native DGAT enzyme is an effective strategy to improve the oil content and value of soybeans.

Surveys of pedigree usage indicate that breeding programs can generate genetic diversity in time. There are also concerns that genetic diversity is being lost. Previous studies of pedigree usage in U.S. maize (Zea mays L.) production have reviewed usage of publicly bred inbred lines. However, proprietary inbred lines were already contributing over 90% of U.S. maize production by 1985. This chronological study of germplasm usage compliments previous studies of genetic diversity in U.S. maize production by reporting the pedigree backgrounds of 68 proprietary, widely used maize hybrids released by Pioneer Hi‐Bred International during the period 1930 to 1999. Objectives are to identify founder sources for the hybrids and to reveal changes in founder contributions through time. We also compare founder usage with pedigrees of widely used U.S. public inbred lines to measure the extent of their reliance on common germplasm backgrounds. Pedigrees of the hybrids collectively traced to at least 61 founders. Several founders of the hybrids had complex pedigrees. Founder backgrounds of the hybrids could be traced to at least 22 landraces with additional contributions from other populations or landraces. Public lines used for comparison traced to 14 founders. Nine founders of the public lines were common in the era hybrids; five were unique to the public lines. Differences in founder contributions were evident for the era hybrids and the public lines. Significant contributions from both the private and public sectors were evident in the pedigrees of the era hybrids. Diversity in time was evident. Hybrids tended to associate by decade of initial release. Most new founder contributions occurred in the 1940s (35%), 1960s (36%), and 1980s (20%). Breeding networks have allowed germplasm that was once exotic to the central Corn Belt to contribute improved productivity in that region.

Despite the importance of grain yield potential to plant breeders and society in general, it has been difficult to identify grain yield quantitative trait loci (QTL) effective for marker‐assisted selection (MAS) across a wide range of genetic and/or environmental contexts. However, as genotyping becomes more cost effective, it might be feasible to use preliminary yield trials to model a target genotype within each context and immediately select the progeny that approach that target genotype in real time. In the present study, elite soybean cultivars with residual heterogeneity were leveraged as populations (the genetic context) to detect yield QTL within a limited set of environments (the environmental context), to model a target genotype, and to select subline haplotypes that comprised the target genotype. The yield potential of the selected subline haplotypes were then compared to their respective mother lines in highly replicated yield trials across multiple environments and years. Statistically significant yield gains of up to 5.8% were confirmed in some of the selected sublines, and two of the improved sublines were released as improved cultivars. This context‐specific MAS (CSM) approach might also be applicable to the more typical biparental and backcross populations commonly used in plant breeding programs. Factors that can affect the efficiency and applicability of CSM are discussed.

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and a decreasing supply (Golbitz, 1999), suggest that oil productivity of soybean should be improved. Previous Protein meal and oil are the two commodities produced from research indicated that seed oil concentration is consoybean [Glycine max (L.) Merr.] that give the crop its value. Increasing seed concentrations of either or both may add value. Objectives trolled by multiple genes with additive inheritance of this study were to investigate the effectiveness of recurrent half- (Brim, 1973). Broad sense heritability estimates (plot sib selection for increased seed oil, to evaluate the effect of tester oil mean basis) for oil content are relatively high (Burton, content on selection response, and to investigate testcross heterosis 1987) and range from 0.47 to 0.89. (Johnson et al., 1955; and inbreeding depression for seed oil content. A recurrent half-sib Kwon and Torrie, 1964;Shorter et al., 1976; Smith and selection system was devised for soybean and selection for increased Weber, 1968). Because of this high heritability, Burton oil content was conducted in a population for seven and three cycles and Brim (1981) developed a recurrent selection proceusing a high and a low-oil tester, respectively. The base population was dure for the rapid increase in oil content using a populaa high-oil composite with gray pubescence (tt) that was segregating for tion segregating for a male-sterile gene, ms 1 . Using this nuclear genetic ms 1 male sterility. In summer, the base population was planted in single plant hills and bordered with the tester (Ms 1 Ms 1 TT) in method, they showed that three cycles of recurrent sea random mating block in North Carolina. About 100 to 200 random lection increased seed oil content 11 g kg Ϫ1 seed and male-sterile plants with hybrid seeds were harvested. Half-sib families found realized heritability estimates for within-family derived from each male-sterile plant were then grown in Puerto Rico and mass selection to be 0.2 and 0.28, respectively. in winter. At maturity, seeds from tawny plants (tester hybrid) were In two populations derived from a base population used to identify half-sib families with high-oil content. Corresponding segregating for ms 1 male sterility, Priadi (1993) comgray plant hybrids from sib matings within the population were bulked pared half-sib family and single selfed-plant recurrent to start the next cycle of selection. Random progenies from the base selection for oil content. Six cycles of recurrent selection populations and selected progenies from each cycle of selection were resulted in a per cycle linear increase of 1.1 Ϯ 0.3 g kg Ϫ1 evaluated in a replicated field experiment at three locations in North Carolina. Cycle ϫ tester hybrids and cycle ϫ cycle sib hybrids were