T. C. Helms

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.

Reaction of Soybean Cultivars to Isolates of Fusarium solani from the Red River Valley

Five isolates of Fusarium solani, originally isolated from diseased soybean roots in the Red River Valley (RRV) of Minnesota and North Dakota, were evaluated for their ability to cause symptoms on 10 genetically diverse soybean cultivars. Taproots of 2-week-old plants were inoculated with F. solani-infested oat kernels, and 3 and 10 weeks later, plants were evaluated for root rot and foliar symptoms. At 3 weeks after inoculation, taproots of all cultivars had extensive reddish brown to black lesions; root rot severity (1-6 scale) ranged from 4.8 to 5.1, and 3.5% of the plants had died. Foliar symptoms were not observed. At 10 weeks after inoculation, all cultivars showed extensive decay of taproots and >50% of lateral roots were necrotic; root rot severity (1-4 scale) ranged from 2.7 to 3.7, and 42.5% of the plants had died. Foliar symptoms were first observed between the R-1 to R-6 growth stages (about 5 weeks after inoculation) on the lower leaves and consisted of chlorosis at the margins that progressed inward. Veins initially were green, but leaves eventually became chlorotic, then necrotic, and fell with petioles still attached to the stem. In some cases, all of the foliage died. There was no significant (P = 0.05) isolate × cultivar interaction for root rot at 3 or 10 weeks after inoculation or for severity of foliar symptoms. Thirty-three cultivars commonly grown in southern Minnesota and the RRV were evaluated for reaction to one isolate of F. solani. Root rot severity ranged from 4.2 to 5.7 (1-6 scale) and 3.5 to 4.0 (1-4 scale), at 3 and 9 weeks after inoculation, respectively, and >50% of the plants died by 9 weeks after inoculation. Severity of foliar symptoms was low. These results indicate that isolates of F. solani from the RRV cause root rot and foliar symptoms on soybean and that cultivars grown in the region lack resistance to this pathogen. Foliar symptoms were not identical to those associated with sudden death syndrome.

Effect of Sclerotinia Stem Rot on Yield of Soybean Inoculated at Different Growth Stages

The effects of Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, on yield of soybean were evaluated in the field with two cultivars in maturity group 0. Plants were inoculated at two growth stages, R3 and R5, using two inoculation methods. Seed weight, seed and pod numbers, seed protein, and oil content were measured. The effects of disease on yield were variable. Disease resulted in significant seed weight loss, with reductions per diseased plant ranging from 18.8 to 38.6%. The estimated yield loss per 10% disease incidence ranged from 83.2 to 229.0 kg/ha, with an average loss of 136.6 kg/ha for four field experiments. A reduction in the number of seeds and pods per plant and seed oil content occurred in some, but not all, experiments. Seed protein was not affected. When disease reduced seed weight, seed and pod numbers, or oil content, there was no growth stage × treatment interaction in the experiments, indicating that inoculation at R5 compared with R3 had a similar effect on yield.

Genetic variance, coefficient of parentage, and genetic distance of six soybean populations

Plant breeders would like to predict which biparental populations will have the largest genetic variance. If the population genetic variance could be predicted using coefficient of parentage or genetic distance estimates based on molecular marker data, breeders could choose parents that produced segregating populations with a large genetic variance. Three biparental soybean Glycine max (L.) Merr. populations were developed by crossing parents that were closely related, based on pedigree relationships. Three additional biparental populations were developed by crossing parents that were assumed to be unrelated. The genetic variance of each population was estimated for yield, lodging, physiological maturity, and plant height. Coefficient of parentage was calculated for each pair of parents used to develop the segregating populations. Genetic distance was determined, based on the number of random amplified polymorphic markers (RAPD) that were polymorphic for each pair of parents. Genetic distance was not associated with the coefficient of parentage or the magnitude of the genetic variance. The genetic variance pooled across the three closely related populations was smaller than the genetic variance pooled across the three populations derived from crossing unrelated parents for all four traits that were evaluated.

Impact of Rag1 Aphid Resistant Soybeans on Binodoxys communis (Hymenoptera: Braconidae), a Parasitoid of Soybean Aphid (Hemiptera: Aphididae)

ABSTRACT Multiple strategies are being developed for pest management of the soybean aphid, Aphis glycines Matsumura; however, there has been little published research thus far to determine how such strategies may influence each other, thereby complicating their potential effectiveness. A susceptible soybean (Glycine max L.) variety without the Rag1 gene and a near isogenic resistant soybean variety with the Rag1 gene were evaluated in the laboratory for their effects on the fitness of the soybean aphid parasitoid, Binodoxys communis (Gahan). The presence or absence of the Rag1 gene was verified by quantifying soybean aphid growth. To test for fitness effects, parasitoids were allowed to attack soybean aphids on either a susceptible or resistant plant for 24 h and then aphids were kept on the same plant throughout parasitoid development. Parasitoid fitness was measured by mummy and adult parasitoid production, adult parasitoid emergence, development time, and adult size. Parasitoids that attacked soybean aphids on susceptible plants produced more mummies, more adult parasitoids, and had a higher emergence rate compared with those on resistant plants. Adult parasitoids that emerged from resistant plants took 1 d longer and were smaller compared with those from susceptible plants. This study suggests that biological control by B. communis may be compromised when host plant resistance is widely used for pest management of soybean aphids.

Seed iron in diverse soybean genotypes

ABSTRACT Iron (Fe) in the embryo fraction of soybean (Glycine max L.) seed is important for seedling growth. Seed Fe accumulation in 27 soybean genotypes differing in seed size was studied at two field locations. Mean seed weight was 148 mg seed−1 with mean individual genotypic values ranging from 68 to 217 mg seed−1. Percentage of total seed dry matter in the seed-coat fraction, which was inversely correlated with individual seed weight, was 8.2%, with mean individual genotypic values ranging from 7.0% to 12.4%. Mean seed-Fe concentration [Fe] was 65 μg Fe g−1, with individual genotypic values ranging from 48 to 81 μg Fe g−1. Seed Fe relative to dry-matter distribution was much more concentrated in seed coats than in embryos of all genotypes. Mean percentage of total seed Fe located in the seed-coat fraction was 29%, with mean genotypic values ranging from 23% to 38%. Neither seed-Fe characteristic was correlated with individual seed weight. Seed [Fe] was not correlated with seed-manganese (Mn) concentration [Mn]. Mean seed [Fe] for the 27 genotypes was different at the two locations, presumably due to differences in available soil Fe. Both genotype and environment affected seed [Fe] of soybean. Soybean seed coats, a major by-product after oil extraction, are a possible rich source of Fe for human nutrition.

Marker-assisted versus phenotypic selection for iron-deficiency chlorosis in soybean

Iron-deficiency chlorosis (IDC) is an important agronomic trait when soybean (Glycine max (L.) Merr.) is planted on calcareous soil. Breeders need confirmation that marker-QTL (quantitative trait loci) associations developed using association mapping, will be effective in a different set of genotypes than the ones used to identify those markers. Marker-QTL associations that had previously been identified in separate mapping experiments were evaluated. Marker-assisted selection (MAS) was compared to phenotypic selection (PS) to evaluate the association mapping approach to identifying markers. The PS or MAS criteria were used to select the 20 most IDC-tolerant and IDC-susceptible lines, based on three 2009 selection sites. Three sites in 2010 were used as validation to compare the effectiveness of the different selection criteria. A random sample (RS) was generated as a control. When validation was conducted averaged across three 2010 sites, PS was the best method to select for IDC with a mean of 1.78, compared to MAS with a mean of 2.05. Since PS was so effective the process of genotyping, which is required for MAS, was unnecessary. The additive effects of QTL that had been estimated from the original mapping experiments were biased upward when compared to QTL effects estimated from the 2009 data. Also, many markers in the target population of experimental lines did not have a gene frequency of 0.5, which greatly reduced the effectiveness of MAS.

Seed Zinc of Soybean as an Indicator of Zinc Status of the Mother Plant

ABSTRACT Evaluation of soybean (Glycine max L.) genotypes for iron (Fe) deficiency can be influenced by zinc (Zn) deficiency. Post-harvest analysis for seed-Zn concentration [Zn] is one way to assess the likelihood that Zn deficiency interfered with genotype assessment. A greenhouse study was conducted on a calcareous soil low in available Zn to determine the influence of ZnSO4 (0, 1, 2, 4, and 8 mg Zn kg−1) on growth and seed [Zn] of three soybean genotypes differing in seed size (BS-8920H—large; MK1009HP—intermediate; and EX9228N—small). Maximum seed yields were obtained with 2 mg ZnSO4-Zn kg−1 for all three genotypes. Severity of Zn-deficiency symptoms in the absence of Zn fertilizer was less pronounced in BS-8920H than in MK1009HP and EX9228N. The relative response to Zn fertilizer was also least with BS-8920H, the large-seeded genotype. However, critical seed [Zn] values were similar for the three genotypes. Seed [Zn] of 31 to 33 mg Zn kg−1 or greater indicated that seed yield was not affected by Zn deficiency. This adequacy range for seed [Zn] was markedly lower than a reportedly critical seed [Zn] value for soybean of 43 mg Zn kg−1. Seed [Zn] was determined in 27 soybean genotypes from two yield trials conducted on calcareous soils with 0.60 and 0.45 mg DTPA-Zn kg−1, respectively. Seed [Zn] data indicated that Zn deficiency had possibly affected seed yields of some genotypes at the lower soil-Zn site.

Cold Hardiness and the Effects of a Low-input Regime on 15 Tall, Warm-season, Native and Ornamental Grasses in the Upper Midwestern United States

Fifteen tall, warm-season, native and ornamental grasses were subjected to a 3-year, low-input, and cold hardiness trial conducted from 2010 to 2013 in zone 4a at Fargo and Mandan, ND. Grasses tested were big bluestem [species (Andropogon gerardii)], ‘Pawnee’ big bluestem (A. gerardii), silver banner grass (Miscanthus sacchariflorus), giant miscanthus (Miscanthus ·giganteus), hardy pampas grass, (Saccharum ravennae), and the following maidengrass (Miscanthus sinensis) cultivars: Silver Feather, Narrow Leaf, Blondo, Autumn Light, Condensatus, Grosse Fontaine, Morning Light, Gracillimus, Strictus, and Zebrinus. In addition to survival, the grasses were also rated for spring vigor and fall quality (0– 10 scale for both evaluations), fall leaf length, and fall flower height. The grasses received no management during the trial other than irrigation during the first season and weed control. The grasses were exposed to subsurface soil temperatures (at 6-inch depth) that reached as low asL8.6 C at the Fargo location andL6 C at the Mandan location. The study revealed that all big bluestem (species), ‘Pawnee’ big bluestem, and silver banner grass survived at both locations; silver banner grass scored the highest spring vigor ratings; silver banner grass and ‘Pawnee’ big bluestem scored the highest fall quality ratings; silver banner grass produced the longest fall leaf length; and ‘Pawnee’ big bluestem, big bluestem (species), and silver banner grass produced the tallest fall flowers.

Relative precision of linkage mapping in recombinant diploid populations

With the increased effort in mapping linked loci, it is important to understand how the precision of the estimate of linkage intensity is influenced by the level of inbreeding and the sample size. For discreet traits, such as molecular markers, the standard error of linkage intensity has been determined for an F2 and backcross population. However, the standard error of linkage intensity has not been determined for discreet traits in the case of the F3 population, double haploid or recombinant inbred lines. The objective is to provide information to aid plant scientists in planning mapping experiments where a given level of precision is desired when estimating the intensity of linkage between two loci for F2 and F3 populations as well as double haploid and fully inbred lines. The precision associated with the estimate of the intensity of linkage is shown graphically as the type of population, the sample size, the intensity of linkage and the linkage-phase is varied. For discreet traits, such as molecular m...