A. Hou

Genetic structure and diversity of cultivated soybean ( Glycine max (L.) Merr.) landraces in China

The Chinese genebank contains 23,587 soybean landraces collected from 29 provinces. In this study, a representative collection of 1,863 landraces were assessed for genetic diversity and genetic differentiation in order to provide useful information for effective management and utilization. A total of 1,160 SSR alleles at 59 SSR loci were detected including 97 unique and 485 low-frequency alleles, which indicated great richness and uniqueness of genetic variation in this core collection. Seven clusters were inferred by STRUCTURE analysis, which is in good agreement with a neighbor-joining tree. The cluster subdivision was also supported by highly significant pairwise Fst values and was generally in accordance with differences in planting area and sowing season. The cluster HSuM, which contains accessions collected from the region between 32.0 and 40.5°N, 105.4 and 122.2°E along the central and downstream parts of the Yellow River, was the most genetically diverse of the seven clusters. This provides the first molecular evidence for the hypotheses that the origin of cultivated soybean is the Yellow River region. A high proportion (95.1%) of pairs of alleles from different loci was in LD in the complete dataset. This was mostly due to overall population structure, since the number of locus pairs in LD was reduced sharply within each of the clusters compared to the complete dataset. This shows that population structure needs to be accounted for in association studies conducted within this collection. The low value of LD within the clusters can be seen as evidence that much of the recombination events in the past have been maintained in soybean, fixed in homozygous self-fertilizing landraces.

Sugar Variation in Soybean Seed Assessed with a Rapid Extraction and Quantification Method

Sugar content in soybean [Glycine max (L) Merr.] seed is an important quality attribute for soyfood and feed. Rapid extraction and quantification of soluble sugars in soybean seed are essential for large-scale breeding selections. In this study, using water as extractant combined with a high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) system, variability and repeatability of sugar content were tested in 20 diverse soybean genotypes. Individual sugars were clearly resolved and identified, including sucrose, stachyose, raffinose, glucose, fructose, and verbascose. Analysis of variance (ANOVA) revealed a highly reproducible estimation of sucrose, stachyose, and raffinose. PI 243545 was confirmed as a unique germplasm with the highest sucrose (105.48 mg/g) and total sugar (148.76 mg/g) content. Two low-oligosaccharide accessions, PI 200508 and 03CB-14, were confirmed with extremely low concentrations of raffinose and stachyose. PI 417559 was identified as a high glucose and fructose germplasm. The identified germplasm with unique sugar profiles will be valuable in breeding specialty soybeans for improved sugar content. The sugar testing method will facilitate the screening of seed sugar profiles in a large-scale soybean breeding program.

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

Abstract 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.

Irrigation and Planting Date Effects on Seed Yield and Agronomic Traits of Early-Maturing Soybean

ABSTRACT Soybean [Glycine max (L.) Merr.] growers in the mid-south United States have increasingly practiced early planting and double-cropping systems. Information on crop management is desired by soybean growers to improve production and profitability. Effects of irrigation and planting date on seed yield and other agronomic traits were investigated in soybean cultivars from eight maturity groups (MG) in 2002 and 2003 at two locations in Arkansas. The planting date (April, May, and June) and irrigation treatments significantly affected seed yield, plant height, and maturity. Significant effects were also observed for number of nodes, number of pods, and number of seeds per plant, whereas number of branches per plant was not affected by planting date and irrigation treatments. Irrigation improved seed yield by an average of 83% (986 kg/ha) in all experiments conducted across two years. Highest seed yield was achieved when soybeans were planted in May, followed by April and then by June planting. The MG V and VI cultivars, conventionally grown in Arkansas, produced higher seed yields than other maturity groups and were the most suitable cultivar selections when considering seed yield alone. Significant interactions were observed among planting date, irrigation, and maturity groups/genotypes. The MG IV was a better candidate for the double-cropping system (June-planting) because of its earlier maturity and high seed yield. For the early soybean production system (April-planting), MG I and II cultivars were potentially good selections because of their short growing periods and acceptable seed yields. The various planting dates and irrigation systems combined with proper cultivar selections provide soybean producers with more options for using the land and water efficiently.

Genetic Diversity Among Popular Historical Southern U.S. Soybean Cultivars Using AFLP Markers

ABSTRACT Modern soybean [Glycine max (L.) Merr.] breeding extensively uses as crossing parents superior cultivars and breeding lines with locally adapted desirable traits, which may lead to declined genetic diversity and increased frequency of fixed common alleles. The main objective of this research was to evaluate, via amplified fragment length polymorphism (AFLP) markers, the genetic diversity and the genetic relationships among the 38 most popular cultivars and lines in the southern United States. Genetic analysis using AFLP markers with 16 primer combinations revealed an average genetic distance of 0.124 among the 38 genotypes examined. Genetic diversity declined among cultivars released during the 1950s and 1960s compared to those released before the 1950s, but increased in the 1970s and peaked in the 1980s, followed by a decline again in the 1990s and 2000s. While 34 unique bands were identified, allelic frequency analysis revealed 50.8% of the 754 loci examined to be fixed in all 38 genotypes. Future parent selection for crossing should consider using genotypes of greater genetic distance and avoid using lines with common genetic background.

Planting Date and Irrigation Effects on Seed Quality of Early-Maturing Soybean in the Mid-South USA

ABSTRACT Information is lacking in soybean [Glycine max (L) Merr.] on whether or not variety selection and management practices can improve seed quality in early production systems. Effects of planting date, irrigation, genotype and maturity on seed quality traits in soybean were investigated in Arkansas for two years. Irrigation (I), planting dates (PD), and maturity groups/genotypes (MG/G) significantly affected seed quality traits. The MG/G, followed by I and PD treatments, made the largest contribution to variations in seed quality traits. Irrigation and late planting significantly improved seed standard and cold germination for most maturity groups. Irrigation also tended to increase seed protein content, whereas planting dates had no impact on seed protein and oil content. Both irrigation and planting dates had little or no effect on visual seed quality and seed pathogen infection. Maturity group and genotype significantly affected all seed quality traits. Late-maturing genotypes exhibited significantly higher standard and cold germination rate, fewer pathogen-infected seed, and better visual seed quality than early-maturing genotypes. Wide-row spacing improved seed germination. Seed germination and vigor of early-maturing genotypes decreased, whereas those of late-maturity genotypes improved when planting was delayed from April to June. Early-maturing genotypes were more responsive to irrigation when planted late. Significant correlation was found between cold and standard germination with other seed quality traits, including visual seed quality rating, disease-free seeds, and Phomopsis-infected seeds. We demonstrated that variety selection and irrigation were important in achieving high seed quality of early-maturing soybeans.

Interaction between two strains of Soybean mosaic virus in soybean

Interactions between two Soybean mosaic virus (SMV) strains, G1 and G7, were studied in nine soybean genotypes (Glycine max) using mixed or sequential inoculations. Six combinations of reactions to the two strains were observed when plants were inoculated with G1 or G7 individually: SS (‘Essex’, susceptible to both strains), RS (‘York’, ‘Prolina’, and ‘Dillon’, resistant to G1 and susceptible to G7), SR (L29 and CNS, susceptible to G1 and resistant to G7), RN (PI 96983, resistant to G1 and necrotic to G7), NR (PI 61944, necrotic to G1 and resistant to G7), and RR (V94-5152, resistant to both strains). When inoculated with mixed inoculum of G1 and G7, soybean genotypes of SS, RS, or SR reaction type exhibited susceptible (mosaic) symptoms; genotypes of RN and NR showed necrotic reaction (stem-tip necrosis); and the genotype of RR remained healthy (symptomless). Testing with strain-differentiating soybean genotypes confirmed the presence of both G1 and G7 strains in SS plants, only the mosaic-inducing strain G7 in RS or G1 in SR plants, and only the necrosis-inducing strain G7 in RN or G1 in NR plants. No virus was detected in RR plants. These results indicated that two mosaic-inducing strains could coexist in the same plant but that a mosaic- or necrotic-inducing strain was dominant over the avirulent strain. When inoculated sequentially with two mosaic strains, only the first strain was detected in the SS genotype, indicating cross-protection. Cross-protection was not observed with sequential inoculation of RS, SR, RN, or NR genotypes. Key words: soybean, Glycine max, Soybean mosaic virus, viral interaction, resistance. Les interactions entre deux souches du virus de la mosaïque du soja (VMS), G1 et G7, ont été étudiées chez neuf génotypes de soja (Glycine max), à l’aide d’inoculations mixtes ou séquentielles. Six combinaisons de réactions aux deux souches ont été observées lorsque les plants ont été inoculés individuellement avec G1 ou G7 : SS (‘Essex’, réceptif aux deux souches), RS (‘York’, ‘Prolina’ et ‘Dillon’, réfractaires à G1 et réceptifs à G7), SR (L29 et CNS, réceptifs à G1 et réfractaires à G7), RN (PI 96983, réfractaire à G1 et réaction nécrotique à G7), NR (PI 61944, réaction nécrotique à G1 et réfractaire à G7) et RR (V94-5152, réfractaire aux deux souches). Après avoir été inoculés avec un inoculum mixe de G1 et G7, les génotypes de soja de réactions SS, RS et SR affichaient des symptômes de réceptivité à la mosaïque. Chez les génotypes de réactions RN et NR, la réaction a été nécrotique (nécrose de l’extrémité des tiges). Quant aux génotypes de réaction RR, ils n’ont pas été infectés (aucun symptôme). Des essais effectués avec des génotypes du soja permettant la différenciation des souches ont confirmé la présence des souches G1 et G7 chez les plants du type SS, seulement celle de la souche G7 ou G1 provoquant la mosaïque chez les plants de types RS et SR, respectivement, et seulement la présence de la souche G7 ou G1 provoquant la nécrose chez les plants de types RN et NR, respectivement. Aucun virus n’a été détecté chez les plants du type RR. Ces résultats ont démontré que deux souches provoquant la mosaïque pourraient coexister dans un même plant, mais qu’une souche provoquant la mosaïque ou la nécrose prédominait sur la souche avirulente. Lorsqu’un plant était inoculé consécutivement avec deux souches de mosaïque, seule la première souche était détectée dans le génotype SS, ce qui indiquait une protection croisée. Cette protection croisée n’a pas été observée lors de l’inoculation séquentielle des génotypes RS, SR, RN ou NR. Mots-clés : soja, Glycine max, virus de la mosaïque du soja, interaction virale, résistance.