R. Jay Goos

Association mapping of iron deficiency chlorosis loci in soybean (Glycine max L. Merr.) advanced breeding lines.

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.

Genome-Wide Association Analysis Identifies Candidate Genes Associated with Iron Deficiency Chlorosis in Soybean

Iron deficiency chlorosis (IDC) is a significant 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. Two populations [2005 (n = 143) and 2006 (n = 141)] were evaluated in replicated, multilocation IDC trials. After controlling for population structure and individual relatedness, and selecting statistical models that minimized false positives, 42 and 88 loci, with minor allele frequency >10%, were significant in 2005 and 2006, respectively. The loci accounted for 74.5% of the phenotypic variation in IDC in2005 and 93.8% of the variation in 2006. Nine loci from seven genomic locations were significant in both years. These loci accounted for 43.7% of the variation in 2005 and 47.6% in 2006. 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 significant markers in one or both populations.

FIELD AND LABORATORY STUDIES COMPARING NUTRISPHERE-NITROGEN UREA WITH UREA IN NORTH DAKOTA, ARKANSAS, AND MISSISSIPPI

Nitrification and ammonia volatility are two important impediments to nitrogen (N) use efficiency and crop uptake around the world. Nutrisphere® is a relatively new product whose manufacturer claims both nitrification and urea volatilization inhibiting properties. Urea coated with Nutrisphere is and the resulting fertilizer is called Nutrisphere®-N urea, or Nutrisphere-N (NSN). Eight field studies on spring (Triticum aestivum L.) or durum [T. turgidum L. subsp duram (Desf.) Husn.] wheat in North Dakota, three field studies in Mississippi/Arkansas on rice (Oryza sativa L.), four laboratory experiments in North Dakota and one in Arkansas were conducted to determine the nitrification and urea volatilization inhibiting ability of NSN compared with urea alone. Results of field and laboratory experiments revealed that the product has no nitrification or urea volatilization inhibiting properties at the recommended rates and spring wheat and rice did not benefit from the application of NSN to urea.

SEED TREATMENT, SEEDING RATE, AND CULTIVAR EFFECTS ON IRON DEFICIENCY CHLOROSIS OF SOYBEAN

Iron (Fe) deficiency chlorosis of soybean (Glycine max L. Merr.) is a common problem in the North Central United States. The objectives of these studies were to determine the effectiveness of seed treatment, seeding rate, and cultivar on the severity of chlorosis and yield of soybean grown in wide (76-cm) rows. A study in 1998 showed an early-season reduction in chlorosis when the seed of a susceptible variety (‘Glacier’) was treated with FeEDDHA, but not with Fe citrate. Studies in 1999 showed increases in leaf chlorophyll, crop height, and yield, as seeding rate of Glacier soybean was increased. Studies in 2000 compared the effectiveness of cultivar selection (Glacier, Council, Traill), seeding rate (370,000 versus 740,000 seed ha−1), and FeEDDHA seed treatment (0 versus 0.56 kg ha−1) on chlorosis severity and yield. Cultivar selection was the most effective tool in reducing chlorosis. Chlorosis was the lowest, and yields the highest with the most resistant cultivar, Traill, followed by the moderately resistant cultivar, Council. Increased seeding rate reduced chlorosis of all cultivars and increased the yield of Traill and Glacier. FeEDDHA seed treatment reduced chlorosis at the 2–3 trifoliolate and increased yield at one site. Cultivar selection was the most effective tool for reducing chlorosis, but increased seeding rates gave additional reduction in chlorosis. Chlorosis reduction by 0.56 kg ha−1 of FeEDDHA was short-lived. Higher rates may be needed.

Greenhouse Evaluation of Controlled-Release Iron Fertilizers for Soybean

Abstract Iron (Fe) deficiency chlorosis is a widespread problem for soybean [Glycine max L.(Merr.)] production in the North Central region of the United States. Fertilization options are limited due to the high cost of soil-applied chelates, and inconsistent crop response to foliar sprays. The objective of this study was to evaluate the response of soybean to several inorganic and organic Fe sources applied alone or coated with Polyon® organic polymers. Three greenhouse experiments were performed, using an alkaline Ulen sandy loam soil. Chlorosis was severe in all three experiments. Most of the products tested, such as uncoated ferrous sulfate, polymer-coated ferrous sulfate, or polymer-coated urea-ferrous sulfate, gave small increases in leaf chlorophyll content at the unifoliate or first trifoliolate stage, but not at the second or third trifoliolate stages. The most dramatic increases in leaf chlorophyll content and dry matter production were observed when the soil was amended with uncoated FeEDDHA or with a polymer-coated mixture of ferrous sulfate, ammonium sulfate, and citric acid. It was concluded that polymer-coated ferrous sulfate-ammonium sulfate-citric acid deserves further evaluation.

Effects of Fertilizer Additives on Ammonia Loss after Surface Application of Urea–Ammonium Nitrate Fertilizer

The purpose of this study was to measure the effect of additives on ammonia loss when used with urea–ammonium nitrate fertilizer (UAN). The fertilizer additives were ammonium thiosulfate (ATS), calcium thiosulfate (CaTS), N-(N-butyl) thiophosphoric triamide (Agrotain, AG), AG + CaTS, or a maleic-itaconic copolymer (Nutrisphere-N, NSN). Four greenhouse studies were conducted, with small fertilizer droplets applied to bare soil, large fertilizer droplets applied to bare soil, small fertilizer droplets applied to soil with 50% straw cover, and large fertilizer droplets applied to soil with 50% straw cover. Ammonia volatilizing from the soil surface was trapped in phosphoric acid and determined by steam distillation. Averaged across all four experiments, the percentage reductions of ammonia loss after 14 days, compared to unamended UAN, were 40% for UAN + ATS, 40% for UAN + CaTS, 51% for UAN + AG, 65% for UAN + AG + CaTS, and 11% for UAN + NSN.

Preliminary evaluation of the soil application value of crambe meal.

Crambe (Crambe abyssinica L.) is a specialty oilseed crop. By‐product crambe meal has a high glucosinolate content, restricting its use for animal feed. The purpose of this study was to evaluate crambe meal for various types of soil application. When incubated with soil, crambe meal mineralized more slowly than soybean meal, with an average of 38% of the added nitrogen (N) from crambe meal appearing as mineral N after 12 weeks of incubation, compared with 57% for soybean (Glycine max L. Merr.) meal. Sulfur mineralization from crambe meal was rapid. Bioassays indicated no phytotoxicity to seedlings from crambe meal. In a second experiment, high rates of crambe meal inhibited the nitrification of urea added to soil, but this effect was short‐lived. In a third experiment, crambe meal–ferrous sulfate mixtures applied to calcareous soil partially alleviated iron deficiency chlorosis of soybean, but the response was less than observed with iron–ethylenediaminedi(o‐hydroxyphenylacetic) acid.

EVALUATION OF SOYBEAN CULTIVARS FOR RESISTANCE TO IRON DEFICIENCY CHLOROSIS IN ROWS VERSUS HILLS

Selection of a resistant cultivar is the most practical control measure for iron deficiency chlorosis in soybean (Glycine max L. Merr.). Plant breeders routinely evaluate cultivars for chlorosis resistance in hill plots, but this procedure may overestimate the chlorosis resistance of a cultivar. The objective of this research was to compare the chlorosis scores of soybean cultivars differing in chlorosis resistance, planted in conventional 76-cm rows, or with two, four, or eight plants per hill. In both 2001 and 2002, it was estimated that three plants per hill would give average chlorosis scores most similar to that observed in 76-cm rows. The highest overall precision was given with row plots, and the lowest with two plants per hill. Hill plots are more space-efficient than row plantings, but are much more easily lost due to animal predation.