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Two infectious root diseases that cause significant yield losses worldwide in soybean (Glycine max [L.] Merr.) are charcoal rot caused by Macrophomina phaseolina (Tassi) Goid. and the soybean cyst nematode, caused by Heterodera glycines Ichinohe. The objective of this research was to evaluate resistance to charcoal rot in a set of 120 soybean accessions reported to have resistance to one or more races of soybean cyst nematode so that lines with combined resistance could be identified. These accessions were screened in an infested field in 2006 and 2007. Charcoal rot severity ranged from 1 to 5, where 1 is resistant and 5 susceptible. The results showed that out of the 120 soybean accessions tested for charcoal rot resistance 12 were identified to have moderate levels of resistance, 51 had moderate susceptibility, and 60 were susceptible. Furthermore, the accessions with moderate resistance to charcoal rot had resistance for one to two races of soybean cyst nematode. Within the lines identified with moderate resistance to charcoal rot, nine had a yellow seed coat, a desirable agronomic trait. These lines can be used as parents in soybean breeding programs for developing soybean cultivars with combined resistance to both charcoal rot and soybean cyst nematode.

Isoflavones are secondary metabolites that are abundant in soybean and other legume seeds providing health and nutrition benefits for both humans and animals. The objectives of this study were to construct a single nucleotide polymorphism (SNP)-based genetic linkage map using the ‘Forrest’ by ‘Williams 82’ (F×W82) recombinant inbred line (RIL) population (n = 306), map quantitative trait loci (QTL) for seed daidzein, genistein, glycitein, and total isoflavone contents in two environments over two years (NC-2018 and IL-2020), identify candidate genes for seed isoflavone. The FXW82 SNP-based map was composed of 2075 SNPs and covered 4029.9 cM. A total of 27 QTL that control various seed isoflavone traits have been identified and mapped on chromosomes (Chrs.) 2, 4, 5, 6, 10, 12, 15, 19, and 20 in both NC-2018 (13 QTL) and IL-2020 (14 QTL). The six QTL regions on Chrs. 2, 4, 5, 12, 15, and 19 are novel regions while the other 21 QTL have been identified by other studies using different biparental mapping populations or genome-wide association studies (GWAS). A total of 130 candidate genes involved in isoflavone biosynthetic pathways have been identified on all 20 Chrs. And among them 16 have been identified and located within or close to the QTL identified in this study. Moreover, transcripts from four genes (Glyma.10G058200, Glyma.06G143000, Glyma.06G137100, and Glyma.06G137300) were highly abundant in Forrest and Williams 82 seeds. The identified QTL and four candidate genes will be useful in breeding programs to develop soybean cultivars with high beneficial isoflavone contents.

Charcoal rot is a major disease of soybean (Glycine max) caused by Macrophomina phaseolina and results in significant loss in yield and seed quality. The effects of charcoal rot on seed composition (seed protein, oil, and fatty acids), a component of seed quality, is not well understood. Therefore, the objective of this research was to investigate the impact of charcoal rot on seed protein, oil, and fatty acids in different soybean genotypes differing in their charcoal rot susceptibility under irrigated and non-irrigated conditions. Two field experiments were conducted in 2012 and 2013 in Jackson, TN, USA. Thirteen genotypes differing in charcoal rot resistance (moderately resistant and susceptible) were evaluated. Under non-irrigated conditions, moderately resistant genotypes showed either no change or increased protein and oleic acid but had lower linolenic acid. Under non-irrigated conditions, most of the susceptible genotypes showed lower protein and linolenic acid but higher oleic acid. Most of the moderately resistant genotypes had higher protein than susceptible genotypes under irrigated and non-irrigated conditions but lower oil than susceptible genotypes. The different responses among genotypes for protein, oil, oleic acid, and linolenic acid observed in each year may be due to both genotype tolerance to drought and environmental conditions, especially heat differences in each year (2012 was warmer than 2013). This research showed that the increases in protein and oleic acid and the decrease in linolenic acid may be a possible physiological mechanism underlying the plant’s responses to the charcoal rot infection. This research further helps scientists understand the impact of irrigated and non-irrigated conditions on seed nutrition changes, using resistant and susceptible genotypes.

Soybean seed isoflavones are affected by various factors, but their responses to phosphorus (P) fertilization is largely unknown. A field experiment was conducted at Jackson and Milan in Tennessee from 2008 to 2010 to investigate the effects of P application rates on concentrations and production of individual and total isoflavone in the form of aglycones in soybean seeds on low and high P soils under no-tillage. Five P application rates (0, 10, 20, 30, and 40 kg P ha−1) plus the University of Tennessee recommended P fertilizer rate based on initial soil-test P were arranged in a randomized complete block design with four replicates. Phosphorus application rates exerted more frequent and greater impacts on aglycone concentrations on the low testing P soil at Milan, particularly under the dry year of 2008. Application of 10–20 kg P ha−1 was adequate for producing high individual and total aglycone concentrations in seeds on the low testing P soil. Genistein concentration was more responsive to P fertilization than daidzein and glycitein concentrations. Individual aglycone concentrations were positively correlated (r = 0.25–0.91) among each other. Total aglycone was positively correlated with seed protein but not with oil in concentration. In conclusion, pre-plant fertilization of 10–20 kg P ha−1 is frequently beneficial for producing high concentrations of individual and total aglycones in soybean seeds on low P soils, particularly under dry years, without any significant reductions in other key quality attributes such as protein or oil.

Information on the effects of agricultural practices such as seeding rate (S), row spacing (RS), herbicide apical treatment (T), and nitrogen application (N) on soybean seed nutrition (protein, oil, fatty acids, sugars, and amino acids) is limited. Although seed composition (nutrition) constituents are genetically controlled, agricultural practices and environmental conditions significantly influence the amount and quality of seed nutrition. Therefore, the objective of this research was to understand the responses of these seed composition constituents to these practices, the environment, and cultivar differences. Two-field experiments were conducted, in 2015 and 2016, in Milan, TN, USA. The experiments were irrigated with four replications and included: two soybean cultivars, two seeding rates, three different row spacings, two N rates, and Cobra herbicide apical treatment. The results showed significant effects of S, RS, N, and T on some seed composition constituents, including protein, oleic, linolenic, and stearic acids, sugars, and some amino acids. The current research demonstrated that single or twin row with a seeding rate of 40,000 seeds ha&minus, 1 resulted in higher protein, oleic, some sugars, and some amino acids. However, a high seeding rate of 56,000 seeds ha&minus, 1 resulted in lower protein, oleic acid, some sugars, and some amino acids due to plant competition for soil nutrients. Herbicide apical application of Cobra1X resulted in higher linolenic acid and some amino acids. Application of nitrogen resulted in higher protein, linolenic, and some amino acids. This research is beneficial to the scientific communities, including breeders and physiologists through advancing knowledge on the interactions between cultivars and environment for seed nutritional quality selection, and to soybean producers through consideration of best agricultural management to maintain high seed nutritional qualities.

Charcoal rot, caused by the fungus Macrophomina phaseolina (Tassi) Goid., is a disease of soybean (Glycine max (L.) Merr.) that causes yield loss worldwide. The purpose of this research was to dete...

Charcoal rot (CR), caused by the fungus Macrophomina phaseolina (Tassi) Goid. is a pervasive disease of economic significance on soybeans (Glycine max (L.) Merr.). Similarly, drought is the leading cause of yield loss in soybean worldwide. In this study, CR severity and seed yield were determined in irrigated and non-irrigated environments in 2011, 2012, and 2013 for thirteen soybean genotypes, nine of which were previously determined to be drought tolerant (DT). The objectives were to determine the severity of CR in the putative DT genotypes and to determine the over-all effect of CR on yield in irrigated and non-irrigated environments. Colony Forming Units (CFUs) at reproductive stage R7 were used to assess disease severity and classify each genotype's response to CR. A stress tolerance index (STI) was used to determine the relative impact of soil moisture stress (i.e. no irrigation) on the 13 genotypes. Over all three years in both irrigated and non-irrigated environments, five genotypes were consistently rated as moderately resistant to CR (MRCR) and three genotypes were consistently rated as susceptible to CR (SCR), whereas the responses of the remaining five genotypes varied between MRCR and SCR. Averaged over the three years, there was a wide range (0.36–1.09) of STI values among genotypes. Even though there was a consistent trend, there was a very weak relationship between STI and CFU's at the R7 growth stage. Regression analysis indicated that as CFUs at R7 increased, seed yield decreased, although the relationship was not significant in every year and irrigation environment. Nonetheless, across all years and irrigation environments, a pooled (global) slope indicated a yield loss of 11.5 kg ha−1 for every 1000 CFUs at R7. These data indicated that as CFUs at R7 increased, seed yield decreased in both irrigated and non-irrigated environments. However, as the relationship between CR disease severity and DT was minimal, it may be necessary to select for resistance to both traits using environments where both soil moisture stress and CR are high.

Mycotoxins are toxic secondary metabolites commonly found in corn and known to cause health issues to human and animals. Information on the relationship between corn grain inoculated with mycotoxins and grain nutrients (protein, oil, fatty acids, sugars, and amino acids) in corn hybrids, especially stacked-gene hybrids is very limited. The objective of this study was to investigate the nutritional advantage of stacked-gene hybrids (Stgene) over non-genetically modified organisms (non-GMO) corn or glyphosate-resistant corn (RR). The experiment was conducted in two locations (clay and sandy soils) in 2011, irrigated, and inoculated with toxigenic Aspergillus flavus using four hybrids of stacked-gene, four of RR, and two non-GMO (conventional). Non-inoculated plots were used as control. The results showed that stacked-gene hybrids had no observable nutritional advantage over RR or non-GMO as all hybrid classes accumulated adequate nutrients in their grains; this effect could be due to adequate concentrations of nutrients in the soil. Higher levels of grain protein, carbohydrates (glucose, reducing sugars, and starch), oleic acid, total amino acids, and some minerals were observed under inoculated conditions in clay and sandy soils indicated a possible osmotic adjustment role of these compounds as stress indicators and osmoprotectants under inoculated conditions. Grain nutrients in clay soil were higher than those in sandy soils; nutrient differences could be due to sandy soil possibly suffering drier conditions, especially inoculated soil, reducing nutrient uptake and nutrients mobility to the grain. This study provides advanced knowledge on the relationship between grain nutrients and mycotoxins in corn hybrids. It is also useful to the corn breeders to understand the responses of grain nutrients to fungal diseases in corn hybrids.

The seed nutrition of crops is affected by global climate changes due to elevated CO2 and temperatures. Information on the effects of elevated CO2 and temperature on seed nutrition is very limited in spite of its importance in seed quality and food security. Therefore, the objective of this study was to evaluate the effects of elevated atmospheric CO2 and temperature on seed composition (protein, oil, fatty acids, and sugars) and mineral nutrition in two soybean cultivars under controlled environments. The treatments were ambient CO2 concentrations (360 μmol mol-1) and elevated CO2 concentration (700 μmol mol-1) as well as normal temperature (26/16°C) and elevated temperature (45/35°C). Plants were grown under greenhouse conditions until the R5 stage, and then, transferred to growth chambers until full maturity (R8). Elevated temperature or a combination of elevated temperature and elevated CO2 resulted in a decrease in seed protein and linolenic acid concentrations and an increase in oil and oleic acid in cultivars Williams 82 (MGIII) and Hutcheson (MG V). Seed sucrose, glucose, and fructose decreased, whereas raffinose and stachyose remained relatively stable. Minerals also decreased under elevated CO2 and temperature. Among those that decreased were N, P, K, Zn, Fe, and B. Natural abundance of 15N and 13C isotopes was altered only under high temperature, regardless of CO2 concentration, indicating that changes in nitrogen and carbon metabolism occurred at elevated temperature. The increase in oil and oleic acid and decrease in linolenic acid are desirable, as high oleic acid and low linolenic acid contribute to the stability and longer shelf-life of oil. The combination of low protein and high oil was due to the inverse relationship between them. This study showed that seed composition and seed mineral nutrients can be affected by elevated temperature alone or elevated CO2 and temperature. This information is beneficial for selecting varieties with high seed nutritional qualities and efficient mineral nutrient use and uptake, traits that are related to seed production, seed quality, and food security. Also, it provides further knowledge on the effect of climate change on seed quality.

Frogeye leaf spot (FLS) of soybean, caused by Cercospora sojina, has been a problem in the southern United States for many years and has recently become a greater problem in the northern United States. Cultivars resistant to FLS have been developed for planting in the southern United States and resistance in many of these cultivars is conditioned by the Rcs3 gene. This gene conditions immunity to all known races and isolates of the pathogen. Resistance to C. sojina in soybean genotypes (cultivars and breeding lines) adapted to north-central U.S. production region is unknown. The objectives of this study were to (i) identify maturity group (MG) III, IV, and V soybean genotypes resistant to C. sojina race 11 by field screening at multiple locations over years and (ii) determine whether FLS resistance in these genotypes is likely to be conditioned by the Rcs3 gene. In total, 1,350 genotypes were evaluated for resistance to race 11 in field trials, and 13 MG III, 45 MG IV, and 15 MG V genotypes did not develop symptoms of FLS. Of these, 54 were subsequently tested for the possible presence of Rcs3 using five molecular markers located within 2 centimorgans (cM) of the gene. None of the MG III genotypes tested had the Rcs3 haplotype of cv. Davis, the source of Rcs3; six of the MG IV genotypes and seven of the MG V genotypes had the Rcs3 haplotype. This is the first report of the presence of the Rcs3 haplotype in LN 97-15076 and S99-2281. The soybean genotypes predicted to have the Rcs3 gene and other genotypes with no FLS symptoms in field trials may be useful in developing soybean cultivars with broad resistance to FLS and adapted to the northern United States.

Phomopsis longicolla is a major seed pathogen of soybean (Glycine max) in hot, humid environments. The objective of this study was to monitor the infection and development of P. longicolla on vegetative and reproductive tissues of six cultivars and to determine the relationship between this infection and subsequent seed infection and seed germination. Cultivars were grown for 3 years (2002 to 2004) without irrigation or with irrigation applied at pre- plus postflowering or at postflowering growth stages. P. longicolla was isolated most frequently from leaf, stem, pod, root, and seed. Diaporthe phaseolorum and three unidentified Phomopsis sp. were also isolated. Diaporthe aspalathi, which previously has not been reported on soybean, was also recovered from leaf samples. These isolates, however, were recovered very infrequently. Recovery of P. longicolla from roots was much lower than from leaves, stems, and pods in all years and irrigation environments. The recovery of P. longicolla from seed was affected by irrigation environments. Seed from irrigated plots had more P. longicolla than that from nonirrigated plots. Isolation of P. longicolla from seed was negatively correlated with percentage of seed germination in irrigated environments but not in the nonirrigated environment. Pod infection was correlated with seed infection in all three irrigation environments. Even though infection of leaves and stems increased with increasing moisture availability, such infection did not consistently correlate with seed infection. Seed germination and seed infection were negatively correlated with percent hard seed. This study provided the first demonstration of the seasonal progression of P. longicolla on soybean cultivars grown under three irrigation environments.

Mengistu, A., Smith, J. R., Ray, J. D., and Bellaloui, N. 2011. Seasonal progress of charcoal rot and its impact on soybean productivity. Plant Dis. 95:1159-1166. The seasonal progress of charcoal rot (caused by Macrophomina phaseolina) was measured over two growing seasons in four separate experiments: irrigated infested, irrigated non-infested, non-irrigated infested, and non-irrigated noninfested. Disease was assessed at V5, R1, R3, R5, R6, and R7 growth stages based on colony forming units (CFU) of M. phaseolina recovered from the lower stem and root tissues and the area under the disease progress curve (AUDPC). The population density of M. phaseolina increased slowly from the V5 to R6 growth stages and then rapidly from the R6 to R7 growth stages for all genotypes in all four experiments. Yield loss due to charcoal rot ranged from 6 to 33% in irrigated environments. The extent of yield loss was affected by severity of charcoal rot, which in turn was affected by year. Yield loss due to charcoal rot was consistently measured in all paired comparisons in irrigated environments, suggesting that charcoal rot can be an important disease in irrigated environments. Disease severity based on CFU accounted for more yield loss variation (42%) than did the AUDPC (36%) when used to assess disease. Growth stage R7 was found to be the optimum stage for assessing disease using CFU. In addition, screening soybean genotypes under irrigation environment may have utility in breeding programs where there is a need for evaluating soybean genotypes for both disease resistance and yield. Charcoal rot of soybean (Glycine max (L.) Merr.), caused by Macrophomina phaseolina (Tassi) Goid., is a disease of economic

Information is limited about phosphorus (P) fertilization effects on soybean seed composition. A field experiment was conducted to investigate the effects of P application rates on the concentrations of various fatty acids, protein, and oil in soybean under no-tillage on low and high testing P soils at Jackson and Milan, Tennessee from 2008 through 2011. Five P rates 0, 10, 20, 30, and 40 kg·P·ha-1 plus the recommended P fertilizer rate based on soil P testing results were arranged in a randomized complete block design with four replicates. Protein, oil, and fatty acid concentrations in seed responded differently to P fertilization. In general, protein concentrations were enhanced but oil levels decreased with increased P application rate. Palmitic and oleic concentrations responded positively to P application rate up to a certain level. However, the response of linolenic acid concentration was inconsistent (negative or positive). Stearic concentration was not influenced by P fertilization. Application of 10 kg·P·ha-1 resulted in higher production of protein and palmitic, oleic, and linolenic acids than zero P and the higher P application rates as well on the P deficient soil. Excessive P application rates could lower seed yield and the quality of some attributes in seed. In conclusion, linoleic acid concentration, a key quality attribute in soybean seed for human and animal consumption, can sometimes be enhanced by P fertilization; the indigenous soil P level and P application rate should be taken into account in breeding soybean cultivars with low linolenic acid level.

Interest in using harvest aids (defoliants or crop desiccants) such as paraquat, carfentrazone-ethyl, glyphosate, and sodium chlorate (NaClO3) have become increasingly important to assure harvest efficiency, producer profit, and to maintain seed quality. However, information on the effects of harvest aids on seed nutrition (composition) (protein, oil, fatty acids, sugars, and amino acids) in soybean is very limited. The objective of this research was to investigate the influence of harvest aids on seed protein, oil, fatty acids, sugars, and amino acids in soybean. Our hypothesis was that harvest aid may influence seed nutrition, especially at R6 as at R6 the seeds may still undergo biochemical changes. Field experiments were conducted in 2012 and 2013 under Midsouth USA environmental conditions in which harvest aids were applied at R6 (seed-fill) and R7 (yellow pods) growth stages. Harvest aids applied included an untreated control, 0.28 kg ai ha&minus, 1 of paraquat, 0.28 kg ai ha&minus, 1 of paraquat, and 1.015 kg ai ha&minus, 1 of carfentrazone-ethyl (AIM), 6.72 kg ai ha&minus, 1 sodium chlorate, 1.015 kg ai ha&minus, 1 carfentrazone-ethyl, and 2.0 kg ae ha&minus, 1 glyphosate. Results showed that the application of harvest aids at either R6 or R7 resulted in the alteration of some seed composition such as protein, oil, oleic acid, fructose, and little effects on amino acids. In addition, harvest aids affected seed composition constituents differently depending on year and growth stage. This research demonstrated the possible alteration of some nutrients by harvest aids. This research helps growers and scientists to advance the understanding and management of harvest aids and investigate possible effects of harvest aids on seed nutrition.

Mengistu, A., Kelly, H. M., Bellaloui, N., Arelli, P. R., Reddy, K. N., and Wrather, A. J. 2014. Tillage, fungicide, and cultivar effects on frogeye leaf spot severity and yield in soybean. Plant Dis. 98:1476-1484. Frogeye leaf spot (FLS) of soybean, caused by Cercospora sojina, has been a problem in the southern United States for many years but has become an increasing problem in the northern United States more recently, causing significant yield losses. This increase in disease severity in the northern United States has been attributed to increased utilization of no-till planting and changes in climate. A field study was conducted at the University of Tennessee, Research and Education Center in Milan, TN from 2007 to 2010 to determine severity in tilled and no-till plots treated with or without fungicide at R3 and R5 growth stages. Three FLS-susceptible cultivars, one each in Maturity Groups III, IV, and V, were treated with pyraclostrobin (Headline) fungicide. Analysis of variance using the area under the disease progress curve (AUDPC) indicated no significant difference (P ≤ 0.05) in disease severity between tilled and no-till plots without fungicide. Fungicide did not significantly reduce disease under no-till, but did under tilled plots. This is the first study showing that no-till plots did not reduce or enhance the severity of FLS when no fungicide was applied. Fungicide application significantly reduced (P ≤ 0.05) disease severity and AUDPC and increased yield in tilled plots. The yield gains in tilled, fungicide-treated plots ranged from 1 to 17%. When fungicide was applied, disease severity was not reduced as significantly in no-till as in treated tilled plots, suggesting that fungicide programs under a notill system may require further study to minimize the risk of FLS

Charcoal rot (CR) disease caused by Macrophomina phaseolina is responsible for significant yield losses in soybean production. Among the methods available for controlling this disease, breeding for resistance is the most promising. Progress in breeding efforts has been slow due to the insufficient information available on the genetic mechanisms related to resistance. Genome-wide association studies (GWAS) enable unraveling the genetic architecture of resistance and identification of causal genes. The aims of this study were to identify new sources of resistance to CR in a collection of 459 diverse plant introductions from the USDA Soybean Germplasm Core Collection using field and greenhouse screenings, and to conduct GWAS to identify candidate genes and associated molecular markers. New sources for CR resistance were identified from both field and greenhouse screening from maturity groups I, II, and III. Five significant single nucleotide polymorphism (SNP) and putative candidate genes related to abiotic and biotic stress responses are reported from the field screening; while greenhouse screening revealed eight loci associated with eight candidate gene families, all associated with functions controlling plant defense response. No overlap of markers or genes was observed between field and greenhouse screenings suggesting a complex molecular mechanism underlying resistance to CR in soybean with varied response to different environments; but our findings provide useful information for advancing breeding for CR resistance as well as the genetic mechanism of resistance.

The timing of harvest is a major factor affecting seed quality in soybean, particularly in Midsouthern USA, when rain during harvest period is not uncommon. The objective of this research was to evaluate the effects of time of harvest on soybean seed quality (seed composition, germination, seed coat boron, and lignin) in high germinability (HG) breeding lines (50% exotic) developed under high heat. The hypothesis was that seeds of HG lines possess physiological and genetic traits for a better seed quality at harvest maturity and delayed harvest. A 2-year field experiment was conducted under irrigated conditions. Results showed that, at harvest maturity, the exotic HG lines had higher seed protein, oleic acid, sugars, seed coat boron, and seed coat lignin, but lower seed oil compared with the non-exotic checks (Control), confirming our hypothesis. At 28 days after harvest maturity (delayed harvest), the content of seed protein, oleic acid, sugars, seed coat boron, and seed coat lignin were higher in some of the HG lines compared with the checks, indicating a possible involvement of these seed constituents, especially seed coat boron and seed coat lignin, in maintaining seed coat integrity and protecting seed coat against physical damage. Highly significant positive correlations were found between germination and seed protein, oleic acid, sugars, and seed coat boron and seed coat lignin. Highly significant negative correlation was found between germination and oil, linoleic acid, seed coat wrinkling, shattering, and hard seed. Yields of some HG lines were competitive with checks. This research demonstrated that time of harvesting is an important factor influencing seed protein and oil production. Also, since high oleic acid is desirable for oxidative stability, shelf-life and biodiesel properties, using HG lines could positively influence these important traits. This result should suggest to breeders of some of the advantages of selecting for high seed coat boron and lignin, and inform growers of the importance of timely harvest for maintaining high seed quality.

Although the Early Soybean Production System (ESPS) in the Midsouthern USA increased seed yield under irrigated and non-irrigated conditions, heat stress and drought still lead to poor seed quality in heat sensitive soybean cultivars. Our breeding goal was to identify breeding lines that possess high germination, nutritional quality, and yield potential under high heat and dryland production conditions. Our hypothesis was that breeding lines derived from exotic germplasm might possess physiological and genetic traits allowing for higher seed germinability under high heat conditions. In a two-year field experiment, breeding lines derived from exotic soybean accessions, previously selected for adaptability to the ESPS in maturity groups (MG) III and IV, were grown under non-irrigated conditions. Results showed that three exotic breeding lines had consistently superior germination across two years. These lines had a mean germination percentage of greater than 80%. Two (25-1-1-4-1-1 and 34-3-1-2-4-1) out of the three lines with ≥80% germination in both years maintained high seed protein, oleic acid, N, P, K, B, Cu, and Mo in both years. Significant (P < 0.05) positive correlations were found between germination and oleic acid and with K and Cu in both years. Significant negative correlations were found between germination and linoleic acid, Ca, and hard seed in both years. There were positive correlations between germination and N, P, B, Mo, and palmitic acids only in 2013. A negative correlation was found between germination and green seed damage and linolenic acid in 2013 only. Seed wrinkling was significantly negatively correlated with germination in 2012 only. A lower content of Ca in the seed of high germinability genotypes may explain the lower rates of hard seed in those lines, which could lead to higher germination. Many of the differences in yield, germination, diseases, and seed composition between years are likely due to heat and rainfall differences between years. The results also showed the potential roles of seed minerals, especially K, Ca, B, Cu, and Mo, in maintaining high seed quality. The knowledge gained from this research will help breeders to select for soybean with high seed nutritional qualities and high germinability.

Phomopsis seed decay (PSD) caused by Diaporthe longicolla has been documented as part of a soybean (Glycine max) fungal disease complex that affects the quality of soybean seed. Soybean-producing countries that have not yet documented the presence of PSD impose soybean seed import restrictions to protect their soybean production. The purpose of this study was to determine the frequency of occurrence of Diaporthe spp. in Paraguay. In 2006, 16 isolates of Diaporthe were recovered for the first time from soybean seed in San Alberto, Paraguay in the south-eastern section of the country. The 16 isolates were used to inoculate mature pods harvested from greenhouse grown PSD-susceptible soybean cultivar ‘Maverick’. Among the16 isolates, six isolates (TN 214, TN 218, TN 224, TN 226, TN 227 and TN 229) caused infection on both pods and seeds within pods. Two groups of isolates were identified based on conidial types: isolates that produced only α conidia and isolates that produced both α and β conidia. The...

Alternative methods are needed to assess the severity of charcoal rot disease [Macrophomina phaseolina (Tassi) Goid] in soybean [Glycine max (L.)] plant tissue. The objective of this study was to define the relationship between light reflectance properties and microsclerotia content of soybean stem and root tissue. Understanding that relationship could lead to using spectral reflectance data as a tool to assess the severity of charcoal rot disease in soybean plants, thus reducing human bias associated with qualitative analysis of soybean plant tissue and cost and time issues connected with quantitative analysis. Hyperspectral reflectance measurements (400-2490 nm) were obtained with a non-imaging spectroradiometer of non-diseased and charcoal rot diseased ground stem and root tissue samples of six soybean genotypes (“Clark”, “LD00-3309”, “LG03- 4561-14”, “LG03-4561-19”, “Saline”, and “Y227-1”). Relationships between the reflectance measurements and tissue microsclerotia content were evaluated with Spearman correlation (rs) analysis (p < 0.05). Moderate (rs = ±0.40 to ±0.59), strong (rs = ±0.60 to ±0.79), and very strong (rs = ±0.80 to ±1.00) negative and positive statistically significant (p < 0.05) monotonic relationships were observed between tissue spectral reflectance values and tissue microsclerotia content. Near-infrared and shortwave-infrared wavelengths had the best relationships with microsclerotia content in the ground tissue samples, with consistent results obtained with near-infrared wavelengths in that decreases in near-infrared spectral reflectance values were associated with increases in microsclerotia content in the stem and root tissue of the soybean plants. The findings of this study provided evidence that relationships exist between tissue spectral reflectance and tissue microsclerotia content of soybean plants, supporting spectral reflectance data as a means for assessing variation of microsclerotia content in soybean plants. Future research should focus on the modelling capabilities of the selected wavelengths and on the feasibility of using these wavelengths in machine learning algorithms to differentiate non-diseased from charcoal rot diseased tissue.

Soybean seed is a major source of phytochemical compounds that impact human health nutrition and livestock meal. Charcoal rot is a disease caused by the fungus Macrophomina phaseolina (Tassi) Goid, and thought to infect the plants through roots by a toxin-mediated mechanism, resulting in yield loss and poor seed quality, especially under drought conditions. Limited information is available on the effect of charcoal rot on seed phytochemical compounds and mineral nutrition in soybean. Therefore, the objective of this research was to investigate the effect of charcoal rot infection on seed phenol, seed coat lignin, isoflavones, and minerals using susceptible (S) (DK 3964) and moderately resistant (MR) (AG 3905) maturity group (MG)III soybean cultivars to charcoal rot. A two-year field experiment was conducted, and infested soil with charcoal rot (infested soil conditions, INF) or control (non-infested soil conditions, NINF) was used. The results showed that the moderately resistant genotype had higher concentrations of seed phenolics, total isoflavones, and seed coat lignin under infested and non-infested conditions and under irrigated or non-irrigated conditions compared with the susceptible genotype. The same general trend was found for seed K, Ca, P, Mn, Zn, B, and Cu concentrations in the moderately resistant genotype compared with the susceptible genotype. Our research demonstrated that these seed phytochemical constituents may explain the differences between susceptible and moderately resistant cultivars and may play an important role in the resistance to charcoal rot.

Previous research has shown that the effect of potassium fertilizer on soybean ([Glycine max (L.) Merr.] seed composition (protein, oil, fatty acids, and isoflavones) is still largely unknown. Therefore, the objective of this research was to investigate the effects of potassium application on seed protein, oil, fatty acids, and isoflavones under Midsouth environmental conditions. A three-year experiment was conducted in two locations (Milan, TN and Jackson, TN). Potassium (K) rates were applied in the form of K2O at a rate of 0 (Control, C), 45 (T1), 90 (T2), 134 (T3), and 179 (T4) kg·ha-1 in a randomized complete block design. The results showed that increasing the K application rate did not result in consistent effects on yield. However, increasing K application rate did increase protein, oleic acid, and individual and total isoflavone concentrations at both locations in 2008 and 2009. In Jackson in 2010, the increase of K rate did not change oleic acid, but resulted in an increase in glycitein and genistein isoflavone concentrations. In 2010, increasing K application rate increased protein concentrations, decreased individual and total isoflavones, and did not change oleic acid concentration at Milan. At the highest rate of K, 179 kg·ha-1, yield and some seed composition constituents were negatively impacted. Generally, K concentration in leaves at V5, R1, R3, and seed at harvest maturity stage (R8) increased with the increase of K rate applications. The research demonstrated that K application can alter seed composition, but this alteration depended on location, environmental stress factors, mainly heat and drought, K level in soil, and K application rate. Higher rates of K application may negatively impact seed composition constituents.

Research on factors controlling production and quality of soybean seed phenolics is very limited. The objective of this research was to evaluate phenolic compounds (total phenol, lignin, and isoflavones), and cell wall boron (B) in seed of susceptible (S), moderately resistant (MR), and resistant (R) soybean genotypes to phomopsis seed decay disease under irrigated and non-irrigated conditions. Seeds were evaluated at harvest maturity stage (R8) and 15 days after harvest maturity to test for weathering effects. Results showed that the concentration of seed phenolic compounds was significantly (P ≤ 0.05) higher in R and MR genotypes than S genotypes under irrigated and non-irrigated conditions. Cell wall boron percentage was significantly higher and total boron was significantly lower in S genotypes than MR and R genotypes. The current research demonstrated that genotypes with higher phomopsis seed infection had lower phenolic compounds, indicating a possible association of these compounds with disease def...

The objective of this research was to evaluate the effect of drought and Phomopsis on seed composition constituents in Phomopsis susceptible (S), moderately resistant (MR), and resistant (R) soybean genotypes grown under irrigated and non-irrigated environments. Genotypes of maturity group (MG) III and V were grown under field conditions in 2003 and 2005. Seed protein, oil, fatty acids, sugars, and minerals were evaluated in seeds harvested at harvest maturity (R8) and 15 days after harvest maturity (delayed harvesting). The results showed that seed protein and oleic acid were higher in S than in MR or R genotypes at 15 days after harvest maturity in MG III in non-irrigated soybean. For MG V genotypes, seed protein, oil, and oleic acid were higher and linoleic and linolenic acids were lower in MR and R than in S in irrigated and non-irrigated soybean at harvest maturity and 15 days after harvest maturity. In MG III genotypes, seed sucrose, raffinose, and stachyose were higher in MR and R than in S genotyp...

Charcoal rot disease in soybean is caused by the fungus Macrophomina phaseolina, which is believed to infect plants from soil through the roots by a toxin-mediated mechanism. Soybean genotypes exist which are susceptible (S) or moderately resistant (MR) to charcoal rot, but the mechanism of resistance is not known. Significantly (p ≤ 0.05) higher levels of phenolics, seed coat lignin, isoflavones, sugars, and total boron were observed in MR genotype than in S genotype seeds under irrigated and nonirrigated and under experimental M. phaseolina infested and noninfested conditions, indicating a possible association of these substances with resistance to toxin-mediated infection.

The cause of poor seed quality (germination) of soybean produced in the Early Soybean Production System in the midsouth U.S.A. is still not completely understood. Temperature, solar radiation, and soybean genotype may all be important factors involved. The objective of this research was to evaluate seed composition, mineral level, and nitrogen assimilation in high and low germinability soybean plant introductions in a full-sunlight (unshaded) and a low-light intensity (shaded) environments. Shade netting was employed in field plots that reduced light intensity by about 50% and air temperature by about 10?F/6?C (10%). A two-year field experiment was conducted on soybean accessions with high germinability (PI 587982A and PI 603723), low germinability (PI 80480 and PI 84976-1), and on soybean cultivars (DSR-3100 RR STS and Pella 86). Results showed that shade resulted in higher total oil, linoleic and linolenic acids, and lower protein and oleic acid. Shade also resulted in lower nitrogen assimilation, leaf chlorophyll concentration, but unshade resulted in higher total seed boron, iron, and nitrogen concentrations. Seed structural boron was positively correlated with germination and protein. Structural boron percentage was consistently higher under shade than under unshade in PI 80480, PI 84976-1, DSR-3100 RR STS, and Pella 86, but consistently higher under unshade than under shade in higher germinability lines PI 587982A and PI 603723, suggesting that different distribution mechanisms of structural boron exist between genotypes. The positive correlation between germination and structural B and between protein and structural B signify a possible role of B in seed quality traits. Our research demonstrated that light intensity, combined with temperature, can alter seed constituents. Higher germinability lines had higher germination rates and lower percentages of hardseededness, desirable traits for soybean seed.

Frogeye leaf spot (FLS) of soybean [Glycine max (L.) Merr.], caused by Cercospora sojina K. Hara, has been a problem in the southern United States for many years. Cultivars resistant to FLS have been developed for planting in this area, and resistance in many of these cultivars is conditioned by the Rcs3 allele at the Rcs3 locus, which provides immunity to all known races of the pathogen. Frogeye leaf spot has recently become a greater problem in the northern United States, and few C. sojina resistant cultivars and breeding lines adapted to this area have been identified. The objectives of this study were to (i) identify maturity group (MG) 00 to VII accessions resistant to C. sojina race 11 by field screening at multiple locations over years and (ii) determine if FLS resistance in these accessions is likely to be conditioned by the Rcs3 allele. A total of 522 accessions were evaluated for reaction to race 11 in field trials in Missouri and Illinois during 2006 and 2007, and 84 of these lines did not develop symptoms of FLS and were field screened for reaction to natural inoculum in Tennessee during 2008. Nine accessions of the 84 lines were susceptible. The remaining 75 were subsequently tested for the possible presence of Rcs3 using five molecular markers located within 2 cM of the gene. Of these 75 accessions, only PI 437726, PI 438302B, and PI 494851 had the Rcs3 haplotype of the cultivar Davis, the source of Rcs3. The soybean accessions predicted not to have the Rcs3 allele and with no FLS symptoms in field trials may also be useful in developing soybean cultivars with resistance to FLS.

One hundred and eighty-two microsatellites or simple-sequence-repeat (SSR) markers for Macrophomina phaseolina were developed. These were tested on 24 isolates of M. phaseolina obtained from seven plant species, and the genetic variation of isolates was studied in relation to potential biological processes that could be affected in this fungus. A total of 120 SSR markers were polymorphic, amplifying >90% of the 24 isolates tested. Thirty percent of the markers showed multiple alleles on individual samples. A large number of markers showed unique alleles in isolates collected from pumpkin and snap bean. DNA sequences corresponding to 43 markers had significant hits on BLAST xa nd⁄or BLAST2GO, and the polymorphism of 36 of those markers showed specific allele patterns for one or more plant host origin of the isolates. Additional tests on growth rate and copper resistance of the isolates identified markers that could be related to those traits. In addition, 27 markers were monomorphic and amplified all 24 isolates. Whereas polymorphic markers can be used for population genetics studies of M. phaseolina, the group of 27 monomorphic markers could help in the fast identification of this species in clinical specimens. The SSR markers developed here will enrich the limited molecular marker resource in M. phaseolina and could be used as the basis for more in-depth studies of the host-pathogen interactions of M. phaseolina.

Information on the effect of sulfur (S) or sulfur+nitrogen (S + N) on soybean seed composition is scarce. Thus, the objective of this study was to investigate the effects of S, and S + N fertilizers on soybean [(Glycine max (L.) Merr.)] seed composition in the Early Soybean Production System (ESPS) under irrigated (I) and nonirrigated (NI) environments. Two separate field experiments were conducted from 2005 to 2007. One experiment was irrigated, and the second experiment was nonirrigated. Under I condition, S at a rate of 44.8 kg/ha alone or with N at 112 kg/ha resulted in a consistent increase in seed protein and oleic acid concentrations, and a decrease in oil and linolenic acid concentrations compared with the control (C). For example, in 2006 and compared with the C, application of S + N increased the percentage up to 11.4% and 48.5% for protein and oleic acid, respectively. However, oil concentration decreased by 3%. Protein and oleic acid increase were accompanied by a higher percentage of leaf and seed N and S. Under NI conditions, seed protein and oleic acid concentrations were significantly higher in C than in any S or S + N treatments, but the oil and linolenic acid concentrations were significantly lower. The results indicate that specific rate of S alone or S + N combined can alter seed composition under irrigated or nonirrigated conditions. This knowledge may help plant breeders to develop and release cultivars to suit specific target locations to grow new value-added soybeans or select for specific seed composition traits under specific environmental stress factors such as drought.

Information on the effect of planting date and irrigation on soybean [Glycine max (L.) Merr.] seed composition in the Early Soybean Production System (ESPS) is deficient, and what is available is inconclusive. The objective of this research was to investigate the effects of planting date on seed protein, oil, fatty acids, sugars, and minerals in soybean grown under irrigated (I) and non-irrigated (NI) conditions. A 2-yr field experiment was conducted in Stoneville, MS in 2007 and 2008. Soybean was planted during second week of April (early planting) and second week of May (late planting) each year. Results showed that under irrigated condition, early planting increased seed oil (up to 16% increase) and oleic acid (up to 22.8% increase), but decreased protein (up to 6.6% decrease), linoleic (up to 10.9% decrease) and linolenic acids (up to 27.7% decrease) compared to late planting. Under I conditions, late planting resulted in higher sucrose and raffinose and lower stachyose compared with early planting. Under NI conditions, seed of early planting had higher protein (up to 4% increase) and oleic acid (up to 25% increase) and lower oil (up to10.8% decrease) and linolenic acids (up to 13% decrease) than those of late planting. Under NI, stachyose concentration was higher than sucrose or raffinose, especially in early planting. Under I, early planting resulted in lower leaf and seed B, Fe, and P concentrations compared with those of late planting. Under NI, however, early planting resulted in higher accumulation of leaf B and P, but lower seed B and P compared with those of late planting. This research demonstrated that both irrigation and planting date have a significant influence on seed protein, oil, unsaturated fatty acids, and sugars. Our results suggest that seed of late planting accumulate more B, P, and Fe than those of early planting, and this could be a beneficial gain. Limited translocation of nutrients from leaves to seed under NI is undesirable. Soybean producers may use this information to maintain yield and seed quality, and soybean breeders to select for seed quality traits and mineral translocation efficiency in stress environments.

Phomopsis seed decay (PSD) of soybean (Glycine max L. Merr) is primarily caused by Phomopsis longicolla. Currently, percent seed infection is used as a method for evaluating resistance to PSD. However, researchers need a common system for classifying soybean genotypes for their reaction to P.longicolla that is consistent across environments. The purpose of this research was: (i) to evaluate the reaction of a select set of soybean accessions to P. longicolla, and (ii) determine the effects of irrigation and two harvest regimes (normal and delayed) on seed infection. We propose a classification system for comparing reactions to P. longicolla among accessions based on a Phomopsis seed infection index (PSII), derived by dividing the percent seed infection of each accession by percent seed infection values of susceptible standards selected within early and late maturity groups. Percent seed infection by P. longicolla infection was greater when accessions were irrigated during the growing season and harvested at normal maturity. Some lines such as MO/PSD-0259 were rated as resistant to P. longicolla (7% seed infection) when not irrigated and harvested at maturity, but were rated as susceptible (39% seed infection) with irrigation and delayed harvest. The resistance ratings to P. longicolla using percent seed infection and PSII varied among accessions. SS93-6012, for example, had similar ratings for both (9% seed infection and 16% PSII). PI 416942 exhibited some resistance to P. longicolla based on percent seed infection (8%), but no resistance based on PSII (32%). Accessions PI 594478, Delmar, SS93-6012, SS93-6181, PI 594603A, and PI 594712 were classified by PSII as moderately resistant under irrigation and with delayed harvest. These results indicate that simple comparisons of percent seed infection among accessions without irrigation, without delayed harvest, and without a standard control of a similar maturity group might result in false conclusions about resistance to P. longicolla.

Effects of crop rotation on soybean (Glycine max (L) Merr.) seed composition have not been well investigated. Therefore, the objective of this study was to investigate the effects of soybean-corn (Zea mays L.) rotations on seed protein, oil, and fatty acids composition on soybean. Soybeans were grown at Stoneville, MS, from 2005 to 2008 in five different scheduled cropping sequences. In 2007, following three years of rotation with corn, seed oleic acid percentage was significantly higher in any crop rotation than continuous soybean. The increase of oleic fatty acid ranged from 61 to 68% in 2007, and from 27 to 51% in 2008, depending on the rotation. The increase of oleic acid was accompanied by significant increases in seed concentrations of phosphorus (P), iron (Fe), and boron (B). In 2007, the increase of P ranged from 60 to 75%, Fe from 70 to 72%, and B from 34 to 69%. In 2008, the increase of P ranged from 82 to 106%, Fe from 32 to 84%, and B from 62 to 77%. Continuous soybean had higher linoleic:oleic ratio and linoleic: palmitic + stearic + oleic ratio, indicating that relative quantity of linoleic acid decreased in rotated crops. The total production of protein, oil, stearic and oleic fatty acids was the lowest in continuous soybean. The total production of palmitic acid was inconsistent across years. The results show that soybeancorn rotation affects seed composition by consistently increasing seed oleic fatty acid, P, Fe, and B concentrations. Higher oleic acid, unsaturated fatty acid, is desirable for oil stability and long-shelf storage. The mechanisms of how these nutrients are involved are not yet understood.

SUMMARYSeed composition in soybean [Glycine max (L) Merr.] has not been well investigated under charcoal rot infestation under irrigated and non-irrigated conditions. The objective of the present experiment was to assess seed composition and nitrogen fixation under these conditions. No significant differences in protein levels in the moderately resistant germplasm line DT97-4290 were observed under these conditions. Under irrigation, protein concentration was significantly (P⩽0·05) higher for the susceptible cultivars Egyptian and Pharaoh under non-infested than infested conditions. The opposite response for protein was observed under non-irrigated conditions for Pharaoh. Oleic acid concentration was significantly (P⩽0·001) higher in susceptible cultivars under infested conditions. The concentration of linolenic acid in susceptible cultivars was significantly lower under infested conditions. The enrichment of Delta 15N in susceptible cultivars under infested conditions indicated that nitrogen fixation was substantially inhibited, but soil nitrogen was used for compensating for atmospheric nitrogen inhibition. These results indicate that charcoal rot infection may alter seed composition and nitrogen fixation in soybean. The alteration in seed composition depended on cultivar susceptibility to charcoal rot and irrigation management.

Charcoal rot (Macrophomina phaseolina (Tassi) Goid) of soybean (Glycine max (L.) Merr.) is a disease of economic signifi cance throughout the world. Progress in developing resistant gen- otypes has been hampered because of a lack of reliable and effi cient methods for assessment of soybean genotypes. Researchers need a com- mon system for classifying soybean genotypes for their reaction to M. phaseolina that is consis- tent across environments. We propose a classi- fi cation system based on a colony-forming unit index (CFUI), derived by dividing the colony- forming unit (CFU) value of a given genotype by the CFU value of a susceptible standard. Four other assessment methods were compared and correlated to CFUI: percent height of stem discoloration measured at R7, foliar symptoms taken at R7, area under the disease progress curve based on foliar symptom data collected four times during the growing season up to R7, and the intensity of internal root and stem dis- coloration taken at R7 (root and stem severity (RSS)). Twenty-four soybean genotypes in Matu- rity Groups III through V were evaluated in 2002 and 2003 in naturally and artifi cially infested fi elds. Based on the CFUI, four genotypes were classifi ed as moderately resistant to M. phaseo- lina. Among the disease assessment methods, RSS had the highest correlation with CFUI (r = 0.71 in 2002 and r = 0.69 in 2003). The CFUI provided a good measure of disease resistance across environments but was still time con- suming. The RSS provided a less-accurate but more-rapid alternative that may be suitable for some breeding strategies.

In the midsouth USA, soybean is produced either under irrigated or non-irrigated conditions. The objective of this experiment was to show the utility of supplemental irrigation as an alternative to full-season and non-irrigation to achieve high yield and high seed composition. The effects of irrigation and cultivar differences on soybean yield and seed composition were conducted. Two cultivars (Dwight and Freedom) and three irrigation regimes (full-season irrigation, FS; reproductive stage/supplemental irrigation, RI; and non-irrigation, NI) were used. Protein percentage was higher in Dwight under FS and RI than NI. In Freedom, protein percentage was higher under NI than under FS and RI. Under NI, Freedom had higher protein percentage than Dwight, especially in 2004, but lower oil in 2003 and 2004. Cultivars showed significant differences in fatty acids. Yield in Freedom under FS and RI was not significantly different. Nitrogen fixation was substantially higher under NI conditions. The results indicate that irrigation management and cultivar selection significantly affect seed composition and yield. Protein increase in Freedom under non-irrigated conditions may benefit producers for high protein seed under dry-land conditions. Supplemental irrigation at the reproductive stage may be a possible alternative for full season irrigation for the cultivar Freedom.

The objective of this research was to create a soybean [Glycine max (L.) Merr] genetic resource in the form of a publicly available, well-characterized mapping population specific to maturity groups (MG) used in the early soybean production system. A total of 568 simple sequence repeat (SSR) markers were tested for polymorphism between soybean breeding line DS97-84-1 (MG IV) and germplasm line DT97-4290 (MG IV). A 90-genotype subset of an F2 population from a cross between these lines was evaluated for genetic linkage using 162 polymorphic SSRs, plant height, pod color (L2/l2), flower color (W1/w1) and stem termination (Dt1/dt1). A 1514 cM (Kosambi) genetic map covering 65% of the soybean genome based on 157 linked SSR markers was created. Comparison with the composite soybean genetic map was used to verify map order. Loci for pod color, flower color and stem termination fell in the expected position on the map indicating this is a normally segregating mapping population. Loci for height were identified on linkage groups C2, D1a, D1b, H, L, M and O. MG IV and V soybean genotypes are critical for the early soybean production system widely used in the midsouthern US. However, only two mapping populations have been reported in Soybase for MG IV and V genotypes. Additionally, the parents used in this cross are known to differ in their response to soybean cyst nematode and charcoal rot, which constitute two major pathology threats to Midsouth soybean production. The population and map reported herein represent an important genetic resource for the early soybean production system.

The new Early Soybean Production System (ESPS), developed in the Midsouth USA, including the Mississippi delta, resulted in higher yield under irrigated and non-irrigated conditions. However, information on the effects of the agricultural practices such as row-type (RT: twin- vs. single-row), row-spacing, (RS), seeding rate (SR), soil-type (ST) on seed nutrition under the ESPS environment in the Mississippi delta is very limited. Our previous research in the Mississippi delta showed these agricultural practices altered seed nutrients in one cultivar only. However, whether these effects on seed nutrients will be exhibited by other soybean cultivars with earlier and later maturities across multiple years are not yet known. Therefore, the objective of this research was to evaluate the effects of agricultural practices and cultivar (Cv) differences on seed nutrition in clay and sandy soils under ESPS environment of high heat and drought. Two field experiments were conducted; one experiment was conducted in 2009 and 2010, and the other in 2008, 2009, and 2010 under irrigated conditions. Soybean were grown on 102 cm single-rows and on 25 cm twin-rows with 102 cm centers at seeding rates of 20, 30, 40, and 50 seeds m(-2). Two soybean cultivars (94M80 with earlier maturity; and GP 533 with later maturity) were used. Results showed that increasing seeding rate resulted in increases of protein, sucrose, glucose, raffinose, B, and P concentrations on both single- and twin-rows. However, this increase became either constant or declined at the higher rates (40 and 50 seeds m(-2)). Protein and linolenic acid concentrations were higher in GP 533 than in 94M80 on both row-types, but oil and oleic acid concentrations were in 94M80 than GP 533. Generally, cultivar GP 533 accumulated more seed constituents in seeds than 94M80. In 2010, there were no clear responses of seed nutrients to SR increase in both cultivars, perhaps due to drier year and high heat in 2010. It is concluded that RT and SR can alter seed nutrition under clay and sandy soils, especially under high heat and drought conditions as in the Mississippi delta.

Information on the effects of management practices on soybean seed composition is scarce. Therefore, the objective of this research was to investigate the effects of planting date (PD) and seeding rate (SR) on seed composition (protein, oil, fatty acids, and sugars) and seed minerals (B, P, and Fe) in soybean grown in two row-types (RT) on the Mississippi Delta region of the Midsouth USA. Two field experiments were conducted in 2009 and 2010 on Sharkey clay and Beulah fine sandy loam soil at Stoneville, MS, under irrigated conditions. Soybean were grown in 102 cm single-rows and 25 cm twin-rows in 102 cm centers at seeding rates of 20, 30, 40, and 50 seeds m–2. The results showed that in May and June planting, protein, glucose, P, and B concentrations increased with increased SR, but at the highest seeding rates (40 and 50 seeds m–2), the concentrations remained constant or declined. Palmitic, stearic, and linoleic acid concentrations were the least responsive to SR increases. Early planting resulted in higher oil, oleic acid, sucrose, B, and P on both single and twin-rows. Late planting resulted in higher protein and linolenic acid, but lower oleic acid and oil concentrations. The changes in seed constituents could be due to changes in environmental factors (drought and temperature), and nutrient accumulation in seeds and leaves. The increase of stachyose sugar in 2010 may be due to a drier year and high temperature in 2010 compared to 2009; suggesting the possible role of stachyose as an environmental stress compound. Our research demonstrated that PD, SR, and RT altered some seed constituents, but the level of alteration in each year dependent on environmental factors such as drought and temperature. This information benefits growers and breeders for considering agronomic practices to select for soybean seed nutritional qualities under drought and high heat conditions.

Previous studies have shown that oil concentration and fatty acid profile (composition) change with genotype, environment (mainly heat and drought), and geographical location. The changes in fatty acid composition under these conditions affect fatty acid stability, creating a challenge to the oil processing industry to predict production and oil quality under different environmental conditions. Oil with a lower stability index is subject to oxidation, resulting in degradation of oil, oil-derived products, biodiesel, and biodegradable lubricants. Therefore, the oxidative stability of oil and fatty acid has become a subject of intensive research and a major goal of soybean breeding programs, biotechnology, and soybean oil industry. This chapter summarizes the effects of two major environmental factors; heat and drought on oil content and fatty acid composition in conventional soybean genotypes and gives up to date information on altered fatty acid soybean genotypes on the horizon.

Nontarget injury from glyphosate drift is a concern among growers using non-glyphosate-resistant (non-GR) cultivars. The effects of glyphosate drift on nitrate assimilation and nitrogen fixation potential, nodule mass, and yield of non-GR soybean were assessed in a field trial at Stoneville, MS. A non-GR soybean cultivar 'Delta Pine 4748S' was treated with glyphosate at 12.5% of use rate of 0.84 kg of active ingredient/ha at 3 (V2), 6 (V7), and 8 (R2, full bloom) weeks after planting (WAP) soybean to simulate glyphosate drift. Untreated soybean was used as a control. Soybeans were sampled weekly for 2 weeks after each glyphosate treatment to assess nitrate assimilation and N2 fixation potential. Nitrate assimilation was assessed using in vivo nitrate reductase assay in leaves, stems, roots, and nodules. Nitrogen fixation potential was assessed by measuring nitrogenase activity using the acetylene reduction assay (ARA). Nitrogen content of leaves, shoots, and seed and soybean yield were also determined. In the first sampling date (4 WAP), glyphosate drift caused a significant decrease in NRA in leaves (60%), stems (77%), and nodules (50%), with no decrease in roots. At later growth stages, NRA in leaves was more sensitive to glyphosate drift than stems and roots. Nitrogenase activity was reduced 36-58% by glyphosate treatment at 3 or 6 WAP. However, glyphosate treatment at 8 WAP had no effect on nitrogenase activity. Nitrogen content was affected by glyphosate application only in shoots after the first application. No yield, seed nitrogen, protein, or oil concentration differences were detected. These results suggest that nitrate assimilation and nitrogen fixation potential were significantly reduced by glyphosate drift, with the greatest sensitivity early in vegetative growth. Soybean has the ability to recover from the physiological stress caused by glyphosate drift.

Recent advances in soybean breeding have resulted in genotypes that express the slow-wilting phenotype (trait) under drought stress conditions. The physiological mechanisms of this trait remain unknown due to the complexity of trait × environment interactions. The objective of this research was to investigate nitrogen metabolism and leaf and seed nutrients composition of the slow-wilting soybean genotypes under drought stress conditions. A repeated greenhouse experiment was conducted using check genotypes: NC-Roy (fast wilting), Boggs (intermediate in wilting); and NTCPR94-5157 and N04-9646 (slow-wilting, SLW) genotypes. Plants were either well-watered or drought stressed. Results showed that under well-watered conditions, nitrogen fixation (NF), nitrogen assimilation (NA), and leaf and seed composition differed between genotypes. Under drought stress, NF and NA were higher in NTCPR94-5157 and N04-9646 than in NC-Roy and Boggs. Under severe water stress, however, NA was low in all genotypes. Leaf water potential was significantly lower in checks (-2.00 MPa) than in the SLW genotypes (-1.68 MPa). Leaf and seed concentrations of K, P, Ca, Cu, Na, B were higher in SLW genotypes than in the checks under drought stress conditions. Seed protein, oleic acid, and sugars were higher in SLW genotypes, and oil, linoleic and linolenic acids were lower in SLW genotypes. This research demonstrated that K, P, Ca, Cu, Na, and B may be involved in SLW trait by maintaining homeostasis and osmotic regulation. Maintaining higher leaf water potential in NTCPR94-5157 and N04-9646 under drought stress could be a possible water conservation mechanism to maintain leaf turgor pressure. The increase in osmoregulators such as minerals, raffinose and stachyose, and oleic acid could be beneficial for soybean breeders in selecting for drought stress tolerance.

These data demonstrate occurrence of natural infection of SVNaV in soybean under greenhouse conditions during winter in the absence of field-grown soybeans or any infected host plant within the greenhouse. The observations point to the likelihood that overwintering viruliferous adult thrips may have the potential to serve as a local source of SVNaV; however, the epidemiological significance needs to be determined. Accepted for publication 5 October 2015. Published 14 October 2015.

Limited information is available on the effects of foliar boron (B) application on soybean seed composition. The objective of this research was to investigate the effects of foliar B on seed composition (protein, oil, fatty acids, and sugars). Our hypothesis was that since B is involved in nitrogen and carbon metabolism, it may impact seed composition. A repeated greenhouse experiment was conducted where half of the soybean plants was exposed to water stress (WS) and the other half was well-watered. Foliar boron (FB) in the form of boric acid was applied twice at a rate of 1.1 kg ha(-1). The first application was during flowering stage, and the second application was during seed-fill stage. Treatments were water stressed plants with no FB (WS-B); water stressed plants with FB (WS+B); watered plants without FB (W-B), and watered plants with FB (W+B). The treatment W-B was used as a control. Comparing with WS-B plants, B concentration was the highest in leaves and seed of W+B plants (84% increase in leaves and 73% in seed). Seeds of W+B plants had higher protein (11% increase), oleic acid (27% increase), sucrose (up to 40% increase), glucose, and fructose comparing with W-B. However, seed stachyose concentrations increased by 43% in WS-B plants seed compared with W-B plants. Cell wall (structural) B concentration in leaves was higher in all plants under water stress, especially in WS-B plants where the percentage of cell wall B reached up to 90%. Water stress changed seed δ(15)N and δ(13)C values in both B applied and non-B applied plants, indicating possible effects on nitrogen and carbon metabolism. This research demonstrated that FB increased B accumulation in leaves and seed, and altered seed composition of well-watered and water stressed plants, indicating a possible involvement of B in seed protein, and oleic and linolenic fatty acids. Further research is needed to explain mechanisms of B involvement in seed protein and fatty acids.

Charcoal rot of soybean, caused by Macrophomina phaseolina (Tassi) Goidanich, has been a problem for soybean farmers in the United States for many years. However, recently its incidence and severity has increased in midwestern and north-central states. Most management strategies, including chemical and biological methods and other cultural options, have been ineffective in controlling this disease. Furthermore, soybean is often planted every other year or in monoculture. Although genetic resistance would be the most sustainable control strategy, resistant commercial soybean cultivars are presently unavailable. The objective of this test was to identify resistant accessions from the USDA soybean germplasm collection in Maturity Groups (MG) 00 to VII by field screening in five environments. A total of 628 accessions were evaluated using established methods for reaction to this disease in Missouri and Illinois (2008 to 2009), and in Tennessee (2009). In 2010, accessions with disease severity reactions of 1 to ≤ 2 were selected for further evaluation in Tennessee. Among the 45 accessions identified as resistant and moderately resistant (1 to ≤ 2), ten were further assessed using colony forming units recovered from ground root and stem tissues which was then converted to colony forming unit index (CFUI) and validated their resistance using this bioassay. All ten had CFUI levels ranging from 0 to 18.2, which were significantly lower (P ≤ 0.05) than the moderately resistant accession, DT97-4290, with 31.8. Four selected accessions, PI594302 (MG VII), PI567562A (MG IV), PI506764 (MG VII), and PI567334 (MG VI), had significantly lower (P ≤ 0.05) CFUI of 0, 0.8, 0.8, and 1.5, respectively. This is the first report of soybean accessions with better levels of resistance than the standard released germplasm, DT97-4290. These accessions can serve as additional sources of charcoal rot resistance in future breeding programs. Accepted for publication 20 January 2013. Published 18 March 2013.

Frogeye leaf spot (FLS) caused by Cercospora sojina Hara is a disease of soybean [Glycine max (L.) Merr.] that causes significant seed yield loss in warm, humid environments worldwide. The Rcs3 gene in soybean has been reported to condition resistance to all known races of C. sojina. The objectives of this study were to: (i) identify maturity group (MG) I to VI accessions resistant to C. sojina race 11 by field screening at two locations; and (ii) determine if the FLS resistance of the symptomless soybean accessions is likely to be conditioned by the Rcs3 allele. A total of 260 accessions including 12 differentials were evaluated for reaction to race 11 in field trials in Missouri and Illinois during 2009, and 20 accessions that did not develop symptoms were retested in 2010 to validate their resistance. The 20 accessions remained resistant and were tested for the potential presence of Rcs3 allele using molecular markers; and none was predicted to carry the Rcs3 allele. These accessions may contain novel loci for FLS resistance and may be used to broaden the base for developing soybean cultivars with frogeye leaf spot resistance. Accepted for publication 16 April 2012. Published 21 May 2012.

Seed-borne diseases of soybeans caused by Phomopsis longicolla (Phomopsis seed decay), Cercospora kukuchii (purple seed stain), and M. phaseolina (charcoal rot) are economically important diseases that affect seed quality. Commercial cultivars marketed as resistant to all three diseases are not available. Reactions of 27 maturity group (MG) III, 30 early MG IV, 33 late MG IV, and 53 MG V genotypes were evaluated for resistance to these pathogens during the 2006 to 2008 growing season in the same field that had been in no-till production, not irrigated, and naturally and artificially infested. There was great variation in seed infection among genotypes and years, indicating the value of screening genotypes over multiple years. Some genotypes were resistant to these pathogens in one, two, or in all three years. Genotypes, DP 3478 (early MG IV), and RO1-769F (MG V) were resistant and DG4460 was moderately resistant to P. longicolla infection across three years. Genotypes AG3705 and FFR3990 (MG III) and DC20300, DC7816, Stoddard, and Ozark (MG V), were resistant to C. kukuchii infection during all three years. Ten genotypes in MG III, eight in early MG IV, seven in late MG IV, and 14 in MG V had no seed infection by M. phaseolina in all three years. These results indicate that seed infection comparison to these pathogens among genotypes should be made over several years, or false conclusions about resistance to any of the three pathogens may be made when disease is assessed for limited period of time. The genotypes identified as having resistance to each or combinations of the seed-borne diseases across the three years could be useful as a source for resistance in improving soybean seed quality. Accepted for publication 20 December 2012. Published 21 March 2012.

Charcoal rot, caused by Macrophomina phaseolina, significantly reduces yield in soybean more than most other diseases in the midsouthern United States. There are no commercial genotypes marketed as resistant to charcoal rot. Reactions of 27 maturity group (MG) III, 29 Early MG IV, 34 Late MG IV, and 59 MG V genotypes were evaluated for M. phaseolina between 2006 and 2008 in a non-irrigated, no-till field that had been artificially infested for three years. There was significant variation in root colonization among genotypes and years, indicating the value of screening genotypes over multiple years. Based on CFUI there was no genotype that was consistently immune to charcoal rot each year. However, there were a total of six genotypes (one genotype in MG III, one in Late MG IV, and four in MG V) that were identified as moderately resistant. Some of the commercial and public genotypes were resistant to M. phaseolina at levels equal to or greater than the standard DT97-4290, a moderately resistant cultivar. The genotypes identified as having moderate resistance across the three years could be useful as sources for developing resistant soybean genotypes. Accepted for publication 27 July 2011. Published 26 September 2011.

All current commercial soybean cultivars are susceptible to charcoal rot, a disease caused by Macrophomina phaseolina. Efforts to manage this disease through non-genetic means have not been effective. However, the combined effects of tillage, cover crop and herbicide use, and their roles in the population dynamics of this fungus have not been fully investigated. A field experiment was conducted in 2002 through 2004 at Stoneville, MS, to determine the population dynamics of Macrophomina phaseolina (Tassi) in soybean stem and root tissues at harvest and in soil at planting and harvest as affected by tillage, cover crop, and herbicide. The tillage treatments were conventional tillage (CT) and no-tillage (NT); the cover crops were hairy vetch, rye, and no cover crop; and the herbicide treatments were glyphosate- and non-glyphosate-based applications. Analysis of variance indicated that there was an effect due to tillage, cover crop, and tillage by year interaction on colony forming units (CFU) of M. phaseolina recovered from soybean tissue. Colony forming units in soybean tissue were greater under the CT than NT and were greater for hairy vetch and no cover crop than rye. Regardless of the cover crop system used, CFU in tissue was greater for CT in 2002 than in 2003 and 2004. Application of glyphosate did not affect the CFU in stem and root tissues or in the soil. The CFU from soil at harvest was significantly higher than at planting. The CFU in soil at planting and harvest was only affected by tillage and not by cover crop system. The CFU from stem and root tissues was greater than in soil suggesting that quantification of CFU in tissue may provide a better estimate of treatment effects at harvest. These results also suggest that charcoal rot may be better managed in the NT rather than in the CT system. Accepted for publication 11 December 2008. Published 30 January 2009.

Soybean [Glycine max (L.) Merr.] seed produced in high-temperature, high-humidity production environments is prone to have substandard germination. Hardseededness, wrinkled seed coats, and infection by Phomopsis longicolla Hobbs are all known to affect soybean seed germinability. Ancestors of modern U.S. soybean cultivars may lack the necessary variability to impart high germinability to new cultivars without the introgression of new genetic diversity. The purpose of this research was to identify soybean germplasm possessing positive traits affecting high seed germinability for seed produced under high-temperature environments, such as in the early soybean production system (ESPS) of the midsouthern United States. Seed was produced in the ESPS for 486 U.S. plant

Frogeye leaf spot, caused by Cercospora sojina, is an economically important foliar disease of soybean (Glycine max (L.) Merr.) in areas where growing conditions are warm and humid. During a survey conducted in 2000 and 2001 in soybean fields in Wisconsin, reddish brown, circular to angular spots varying in diameter from 1 to 5 mm were observed on soybean leaves in four fields in Dane and Iowa counties, and in five and six fields in Lafayette and Green counties, respectively. Soybean plants were in growth stages between R3 and R5 during sampling. Disease incidence ranged from 30 to 100% with 5 to 10% of leaf area covered with leaf spot in 2000. In 2001, trace levels of the disease were detected in Dane County, but no symptomatic plants were present in the other counties. Symptomatic leaves were collected from all locations in 2000 and Dane county in 2001. Ten leaves were randomly picked from all samples for each year, placed in a 100 × 15 mm petri dish dampened with Whatman No.1 filter paper, and incubated overnight at 24°C. Fungal sporulation developed after 24 h. Fifteen spores were removed from the 10 leaves, placed on acidified potato dextrose agar (APDA), and incubated in the dark at 24°C. Cultures with dark pigmentation and associated conidia and conidiophores were observed after 3 weeks. The conidiophore, spore type, and leaf symptoms correspond to the description of C. sojina (1). Conidiophores were light-to-dark brown, one to four septate, and fasciculate. The conidiophores were also geniculate and measured 52 to 120 x 4 to 6 μm. Conidia were 0 to 10 septate, hyaline, elongate to fusiform, and measured 40 to 60 x 6 to 8 μm. Cultures were maintained on APDA, and spores for inoculations were produced on this medium. Spores from the 2000 cultures were harvested, bulked together, and used for pathogenicity tests. Pathogenicity tests were conducted in a growth chamber using a known susceptible soybean cultivar, Blackhawk. Ten-cm-diameter pots each containing 4 plants was used. Twenty plants were inoculated and 20 served as noninoculated controls. Ten-day-old plants were inoculated with a spore suspension of 3 × 105 spores/ml by spraying inoculum over the entire leaf surfaces with a spray atomizer. Control plants were sprayed similarly with sterile distilled water. Plants were incubated in an enclosed, transparent fiberglass box with a humidifier that provided 95 to 100% humidity. Lighting in the growth chamber was adjusted to 18-h light and 6-h dark during the inoculation period. Plants were removed from the box after 48 h and placed in a growth chamber with a 12-h photoperiod. The light output in the growth chamber was 300 μmol·m-2·s-1 and the temperature was maintained at 24 ± 3°C. The experiment was repeated once. Typical field symptoms appeared on each of the inoculated plant 8 days after inoculation, while the controls expressed no leaf symptoms. C. sojina was reisolated from all symptomatic plants. To our knowledge, this is the first report of C. sojina from soybean in Wisconsin. Reference: (1) D. V. Phillips. Frogeye leaf spot. Page 20 in: Compendium of Soybean Diseases. 4th ed. G. L. Hartman, J. B. Sinclair, and J. C. Rupe, eds. American Phytopathological Society, St. Paul, MN, 1999.