Elite Soybean Cultivars Research Articles

Molecular basis of the low linolenic acid trait in soybean EMS mutant line RG10

AbstractA possible solution to stability problems is to genetically reduce the content of linolenic acid in soybean seed. RG10 is a low linolenic acid line (<25 g/kg) produced by ethyl methane sulfonate (EMS) treatment of the low linolenic acid EMS mutant line C1640. The objective of this study was to determine the molecular basis of the low linolenic acid trait in RG10. Sequence analyses of mutant RG10 and wild‐type OX948 ω‐fatty acid desaturase (Fad3) genes showed that the low level of linolenic acid in RG10 is likely a result of mutations in two Fad3 genes. A mutation in the Fad3A gene introduces a stop codon in exon 6 that would prematurely terminate translation and a second mutation in the 5′ splice site of intron 5 of the Fad3B gene may result in abnormal mRNA splicing products. Both mutations would result in a non‐functional enzyme. Molecular markers developed for these mutations should simplify and accelerate introgression of the RG10‐based low linolenic acid trait into elite soybean cultivars.

Cloning and sequence diversity analysis of GmHs1 pro-1 in Chinese domesticated and wild soybeans

Soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is the most important pathogen in soybean production worldwide and causes substantial yield losses. An apparent narrow genetic base of SCN resistance was observed in current elite soybean cultivars, and searching for novel SCN resistance genes as well as novel resistance sources rather than focusing on the two important genes rhg1 and Rhg4 has become another major objective in soybean research. In the present paper we report a 1,477 bp Hs1pro-1 homolog, named GmHs1pro-1. This gene was cloned from soybean variety Wenfeng 7 based on information for Hs1pro-1, a beet cyst nematode resistance gene in sugar beet. It has two domains, Hs1pro-1_N and Hs1pro-1_C, both of which are believed to confer resistance to nematodes. Of the 1,477 bp sequence in GmHs1pro-1, an open reading frame of 1,314 bp, encoding a protein with 437 amino acids, was flanked by a 5′-untranslated region of 27 bp and a 3′-untranslated region of 135 bp. Fourteen single-nucleotide polymorphisms (SNPs) were observed in 44 soybean accessions including 23 wild soybeans, 8 landraces, and 13 soybean varieties (or lines), among which 5 in wild soybeans and 3 in landrace accessions were unique. Sequence diversity analysis on the 44 soybean accessions showed π = 0.00168 and θ = 0.00218 for GmHs1pro-1; landraces had the highest diversity, followed by wild soybeans, with varieties (or lines) having the lowest. Although we did not detect a significant effect of selection on GmHs1pro-1 in the three populations, sequence diversity, unique SNPs, and phylogenetic analysis indicated a slight domestication bottleneck and an intensive selection bottleneck. High sequence diversity, more unique SNPs, and broader representation across the phylogenetic tree in wild soybeans and landraces indicated that wild collections and landrace accessions are invaluable germplasm for broadening the genetic base of elite soybean varieties resistant to SCN.

Genetic characterization of ninety elite soybean cultivars using coefficient of parentage

The objective of this work was to estimate the coefficient of parentage and to understand the genetic structure of 90 elite soybean cultivars, which are adapted to different Brazilian environments. A total of 4,005 coefficients of parentage (f) were obtained and used to group the cultivars by UPGMA method. The constructed dendrogram showed several related cultivar groups which shared similar ancestors and clearly showed the genetic structure of the main Brazilian cultivars. Effective population sizes (Ne) were also estimated for cultivars in different generations. The average f = 0.2124 value, obtained from cultivars classified into four decades according to the release year, suggested effective soybean population sizes of 11 and 13 calculated using arithmetic and weighted means, respectively. The relatively small Ne and the high parentage coefficient support the conclusion that there is a high similarity degree among the main soybean cultivars in Brazil.

Intra‐Cultivar Variation for Seed Weight and Other Agronomic Traits within Three Elite Soybean Cultivars

ABSTRACTDespite its importance, exploitation of intra‐cultivar variation has been very limited due to the belief that elite cultivars are highly homogeneous. The main objective of this study was to investigate the presence of exploitable intra‐cultivar variation for seed weight, maturity, and other agronomic traits within elite soybean cultivars released for their superior productivity and resistance to various diseases. Single‐plant progeny lines, selected at very low plant density from within these cultivars, were evaluated for seed weight, maturity, plant height, lodging, and seed yield in row‐plot replicated randomized complete block designs across years. For seed weight, the magnitude of intra‐cultivar variation across years between the largest‐ and the smallest‐seeded lines averaged 36 mg seed−1 for Benning, 22 mg seed−1 for Cook, and 45 mg seed−1 for Haskell. For maturity, the magnitude of intra‐cultivar variation was 5 d in Benning, 4 d in Cook, and 7 d in Haskell. Furthermore, we discovered intra‐cultivar variation for plant height within Cook and Haskell, and for lodging within Haskell. This study is the first one to report evidence of significant intra‐cultivar variation for seed weight, maturity, plant height, and lodging within soybean cultivars. The results suggest that cultivars may not be permanent records with nonexistent variation but genetic material that can be upgraded to maintain uniformity in the long term and further improve desirable agronomic or seed‐trait characteristics.

Yield Potential and Waterlogging Tolerance of Selected Near-Isogenic Lines and Recombinant Inbred Lines from Two Southern Soybean Populations

A quantitative trait locus (QTL) for waterlogging tolerance has been identified in a northern cultivar Archer. In the current study, Archer was crossed with two southern elite soybean cultivars A5403 and P9641 to investigate the efficiency of marker-assisted selection and phenotypic selection for waterlogging tolerance and to assess the value of waterlogging tolerance for soybean yield improvement. Near-isogenic lines (NILs) were created using the linked simple sequence repeat (SSR) marker Sat_064 for the waterlogging tolerance QTL from each of the F6-derived populations. Concurrently, 103 and 67 recombinant inbred lines (RILs) were also generated from Archer × A5403 and Archer × P9641, respectively. Significant variations in seed yield or plant injury were observed among the NILs and RILs under waterlogging stress. The 29 most tolerant and 29 most sensitive NILs and RILs were selected on the basis of waterlogging injury ratings and evaluated under irrigated and waterlogged conditions in Arkansas and Missouri in 2002 and 2003. The most tolerant lines produced an average of 60.9% of their irrigated yield, as compared with only 32.6% and 53.9% by the most sensitive lines and the commercial checks, respectively. Waterlogging injury scores for the tolerant lines, checks, and sensitive lines were 3.6,4.3, and 6.6, respectively, following the same trend as their yield reductions. A genotype-by-environment interaction (G × E) analysis showed that some of the selected lines were highly stable in response to waterlogging stress across environments. Breeding selection for the waterlogging tolerance can be performed in the field based on seed yield and plant injury scores.

Environmental Influences on Isoflavones and Saponins in Soybeans and Their Role in Colon Cancer

Soybeans have long been recognized as an excellent source of high-quality protein. The soybean also contains a wide variety of chemical compounds that have potent bioactivity. Among these compounds are the isoflavones and the saponins. The goal of our research was to quantify isoflavone and saponin concentrations in elite soybean cultivars grown in different environments and to identify a naturally occurring high and low variety that could be used in animal studies of colon cancer. We observed significant environment x genotype interactions for the cultivars and selected 2 that provided the range of concentration for isoflavones and saponins. These were grown in an adequate quantity for animal studies, which are ongoing. We explored the influence of isoflavones and saponins on human colon tumor cells in culture, Caco-2, to determine potential mechanisms through which these compounds influence the carcinogenic process. We observed the inhibition of Caco-2 cell proliferation by isoflavones and saponins, suggesting a protective effect of these compounds in colon cancer. Using purified soy saponins, we found no negative effects on mouse growth, organ weights, or intestinal morphology when the diet contained up to 3% saponins by weight. Hence, soy isoflavones and saponins are likely to be protective of colon cancer and to be well tolerated. Continuing studies will explore the cancer-protective effects of these compounds in animal models.

Divergent selection at ultra-low plant density for seed protein and oil content within soybean cultivars

Soybean [ Glycine max (L.) Merr.] seed is a major source of protein for animal feed and oil for human consumption. Selection within elite soybean cultivars for the improvement of agronomic and seed traits is assumed to be ineffective due to the belief that cultivars are highly homogeneous. Previously reported data suggest that latent variation among the single plant selections within a cultivar exists and that mechanisms that generate de novo variation may also be present. The main objective of this study was to perform divergent single-plant selection at ultra-low plant density and investigate the presence of genetic variation for seed protein and oil within three elite soybean cultivars. A secondary objective was to investigate the variation for fatty acid composition. In 1995, single plants from the three cultivars were grown in a honeycomb design using a plant-to-plant spacing of 0.9 m. A total of 333 plants from ‘Benning’, 392 plants from ‘Haskell’, and 371 plants from ‘Cook’ were evaluated. Divergent single-plant selection for protein and oil content was performed to select a total of 20 plants for high or low protein and 20 plants for high or low oil from each cultivar. The selected plants were further evaluated in replicated row-plot experiments for 3 years. Our results indicate that single-plant selection at low plant density was successful in discovering significant variation for seed protein and oil within each of the three soybean cultivars. For protein content, the magnitude of intra-cultivar variation between the highest- and lowest-protein lines averaged 19 g kg −1 across the three cultivars and ranged from 13 to 24 g kg −1. For oil composition, the magnitude of variation between the most divergent lines averaged 12 g kg −1 across the three cultivars and ranged from 9 to 14 g kg −1. Significant variation among the selected progeny lines was also discovered for specific fatty acid composition. The magnitude of intra-cultivar variation averaged from 6 to 29 g kg −1 across the five fatty acids of soybean. The genetic variation discovered within the soybean cultivars is most likely due to latent variation and/or newly created variation. Our data provide evidence that single-plant selection at ultra-low plant density within elite cultivars can be effective in improving the seed composition of a soybean cultivar.

A study on the effect of genotypes, plant growth regulators and sugars in promoting plant regeneration via organogenesis from soybean cotyledonary nodal callus

We have developed an efficient protocol for callus induction and plant regeneration in three elite soybean cultivars (Williams 82, Loda and Newton). The technique is most novel in that the shoot buds developed from the nodal callus. Callus induction and subsequent shoot bud differentiation were achieved from the proximal end of cotyledonary explants on modified Murashige and Skoog (MS) media containing 2.26 μM 2,4-dichlorophenoxy-acetic acid (2,4-D) and 8.8 μM benzyladenine (BAP), respectively. Varying the carbon source optimized the regeneration system further. Among the various carbon sources tested, sorbitol was found to be the best for callus induction and maltose for plant regeneration.

Genetic Diversity among Elite Brazilian Soybean Cultivars with Narrow Genetic Base

This study was carried out to assess the genetic diversity among elite soybean cultivars with narrow genetic base using prediction techniques involving data from genealogy and agronomic traits. These predictions were then compared to the agronomic diversity observed by growing the derived cross progenies. The cultivars FT-Cristalina, Doko RC, IAC-12, UFV-10 were selected based on their genetic diversity obtained from molecular markers.

Simple Sequence Repeat Diversity among Soybean Plant Introductions and Elite Genotypes

The use of molecular markers to facilitate the introgression of plant introduction (PI) germplasm into elite soybean [Glycine max (L.) Merr.] cultivars will depend on the amount of polymorphism that exists between elite genotypes and PIs. The objective of this study was to assess the simple sequence repeat (SSR) diversity of 39 elite soybean genotypes (Elites) and 40 PIs that were selected for high yield potential. A total of 397 alleles were detected among the 79 genotypes at 74 SSR marker loci. The number of alleles detected among the PIs was 30% greater than that detected among the Elites. There were 138 alleles specific to the PIs that occurred across 60 SSR loci and 32 alleles specific to the Elites that occurred across 27 SSR loci. Average marker diversity among the PIs was 0.56 and ranged from 0.0 to 0.84. Average marker diversity among the Elites was 0.50 and ranged from 0.0 to 0.79. Genetic similarity estimates based on simple matching coefficients revealed more genetic diversity among the PIs than among the Elites. The greatest genetic diversity was between the PIs and Elites. The ability of SSRs to distinguish among elite soybean genotypes and PIs with agronomic merit may assist with the transfer of favorable alleles from PIs into elite soybean cultivars.

Soybean Pedigree Analysis Using Map‐Based Molecular Markers: I. Tracking RFLP Markers in Cultivars

The history of soybean [Glycine max (L.) Merr.] cultivar development is relatively short. Approximately 80% of the germplasm present in modern cultivars can be traced back to just 12 ancestral lines which were introduced into the USA in the early 1900s. This limited number of ancestral contributors and short history make soybean a promising system for marker‐facilitated, pedigree‐based, genetic analysis. The overall objectives of this project were to (i) identify a core set of markers that would be useful for pedigree‐based analyses of elite soybean cultivars, (ii) trace markers and chromosomal regions from ancestral to descendent cultivars, (iii) determine if the observed and theoretical contribution of parental genomes to cultivar progeny were comparable, and (iv) demonstrate the utility of pedigree‐based or codescent mapping in the detection of putative linkages between molecular markers and phenotypic traits. Sixty‐four soybean lines including ancestral and milestone cultivars were analyzed at 217 RFLP loci to identify a core set of markers to use in evaluating these, and other elite breeding lines. A core set of 97 polymorphic loci were identified for genetic analysis. Results demonstrated that genomic regions contributed by a parent can be traced, often for more than a generation. Six generations of cultivar development were included in this analysis, and one RFLP allele, R013‐l‐b, could be traced through all six generations. Results also revealed that two pedigrees, that of Lincoln and Ogden, could not be supported by RFLP analysis, although it is possible that the pedigrees reported are correct and the incorrect accessions are maintained in the USDA collection. Comparison of the predicted amount of germplasm contributed by a parent, and the amount observed by RFLP analysis revealed that in only four out of 26 instances did one parent provide more genetic information than expected. Codescent analysis of markers and phenotypes demonstrated putative linkages with B and Dtl. The ability to follow regions of chromosomes from parent to offspring through multiple generations should provide an understanding of what transpired at the molecular level during the breeding of cultivars over the last 55 yr. Graphical genotypes of the cultivars analyzed in this study, and the raw RFLP data, are available for electronic transfer.