Iron defi ciency chlorosis (IDC) is a signifi cant yield-limiting problem in several major soybean [Glycine max (L.) Merr.] production regions in the United States. Soybean plants display a variety of symptoms that range from a slight yellowing of the leaf to interveinal chlorosis, to stunted growth that reduces yield. The objective of this analysis was to employ single nucleotide polymorphism (SNP)-based genome-wide association mapping to uncover genomic regions associated with IDC tolerance. A number of the loci discovered here mapped at or near previously discovered IDC quantitative trait loci (QTL). A total of 15 genes known to be involved in iron metabolism mapped in the vicinity (<500 kb) of signifi cant markers in one or both populations.

tion, foliar sprays, and seed treatment with FeEDDHA for reducing chlorosis and increasing the yield of soy-Iron-deficiency chlorosis is common when soybean [Glycine max bean planted in narrow rows. (L.) Merr.] is grown on calcareous soils. The objective of this study was to compare the relative effectiveness of cultivar selection, foliar sprays, and FeEDDHA seed treatment for reducing chlorosis and MATERIALS AND METHODS increasing the yield of soybean planted in 15-cm rows. Three cultivars Four field studies were conducted in eastern North Dakota ('Glacier', 'Council', and 'Traill') were grown in a factorial combinaduring the 1999 growing season on sites with a history of tion with two levels of foliar spray (control vs. two FeEDTA sprays) producing Fe-deficiency chlorosis in soybean. The selected and two levels of seed treatment (control vs. FeEDDHA seed treatment). The cultivars gave an expected chlorosis response, with Glacier site characteristics are shown in Table 1. Topsoil (0-15 cm) being the most susceptible, and Traill being the most resistant. Foliar samples were taken from 20 random areas within the experisprays significantly (P Յ 0.05) reduced chlorosis at two sites. Seed mental area, air-dried, crushed (Ͻ2 mm), mixed, subsampled, treatment with FeEDDHA did not reduce chlorosis although this and analyzed by routine soil tests for available nutrients treatment was effective in prior studies with soybean planted in 76-(Dahnke, 1988), CaCO 3 equivalent (Williams, 1949), saturacm rows. Iron treatments did not reduce the chlorosis scores of Glacier tion extract composition (Rhoades, 1982), and particle size to the level of Council or Traill without Fe treatments. Seed yields analysis using the hydrometer method (Day, 1965). The experwere significantly different for cultivars at all sites. Averaged across imental design was a complete factorial of three cultivars ϫ sites and Fe treatments, the yields were 1361, 1913, and 2203 kg ha Ϫ1 , two foliar spray treatments ϫ two FeEDDHA seed treatfor Glacier, Council, and Traill, respectively. Foliar sprays tended to ments. The treatments were arranged in a randomized comincrease the yield of Glacier at two sites and significantly increased plete block design with four replicates. The three cultivars, in the yield of all three cultivars at another site. The yield responses to order of increasing chlorosis resistance, were Glacier (Orf foliar sprays, when obtained, were about 300 kg ha Ϫ1 . FeEDDHAand Denny, 1997), Council (Helms and Halvorson, 1996), and seed treatment did not increase seed yield. Cultivar selection remains Traill (Helms and Nelson, 1998). Screening trials in the greenthe most practical control measure for Fe-deficiency chlorosis of soyhouse indicate that these three cultivars represent the range bean grown in narrow rows.

Association mapping is an alternative to mapping in a biparental population. A key to successful association mapping is to avoid spurious associations by controlling for population structure. Confirming the marker/trait association in an independent population is necessary for the implementation of the marker in other genetic studies. Two independent soybean populations consisting of advanced breeding lines representing the diversity within maturity groups 00, 0, and I were screened in multi-site, replicated field trials to discover molecular markers associated with iron deficiency chlorosis (IDC), a major yield-limiting factor in soybean. Lines with extreme phenotypes were initially screened to identify simple sequence repeat (SSR) markers putatively associated with the IDC. Marker data collected from all lines were used to control for population structure and kinship relationships. Single factor analysis of variance (SFA) and mixed linear model (MLM) analyses were used to discover marker/trait associations. The MLM analyses, which include population structure, kinship or both factors, reduced the number of markers significantly associated with IDC by 50% compared with SFA. With the MLM approach, three markers were found to be associated with IDC in the first population. Two of these markers, Satt114 and Satt239, were also found to be associated with IDC in the second confirmation population. For both populations, those lines with the tolerance allele at both these two marker loci had significantly lower IDC scores than lines with one or no tolerant alleles.

Grain protein of barley (Hordeum vulgare L.) produced for malting often is greater than the industry's acceptable standards of 135 and 130 g kg−1 for six‐rowed and two‐rowed barley, respectively. Environmental conditions such as low rainfall and high temperatures after anthesis often cause increased grain protein. This study was conducted at four dryland environments in North Dakota over 2 yr to compare the effects of N fertilization and planting date on agronomic and malt quality traits of two experimental barley genotypes inherently low in grain protein with two barley cultivars currently grown in the U.S. Midwest. Agronomic traits evaluated were grain protein, grain yield, kernel weight, and kernel plumpness. Malt quality traits evaluated were fine‐grind extract, soluble wort protein, diastatic power (DP), and ɑ‐amylase activity. Nitrogen rates ranged from 0 to 200 kg ha−1. Nitrogen significantly increased grain protein, grain yield, soluble wort N, DP, and ɑ‐amylase activity, and decreased kernel weight, kernel plumpness, and fine‐grind malt extract. Significant genotypes differences were observed for all traits. The N × genotype interaction was significant for all agronomic traits, soluble wort N, and DP. The standard cultivars had greater than the acceptable grain protein when fertilized with 150 or 200 kg N ha−1. Delaying planting significantly decreased grain yield and fine‐grind malt extract. Grain protein of the low‐protein genotypes was within the limit desired by the malting and brewing industry at all N rates and planting dates. Thus, protein levels acceptable to maltsters can be obtained for low‐protein barley genotypes when excessive N is available and growing conditions are unfavorable.

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