Location: Soybean and Nitrogen Fixation Research2010 Annual Report
1a. Objectives (from AD-416)
Objective 1, the improvement of yield potential, will deal with QTL analysis of breeding populations derived from exotic germplasm and with a method to identify appropriate exotic germplasm for study. Objective 2, the improvement of seed composition, will focus on raising oleic acid content of soy oil, reducing phytate in the protein meal, and in determining the impact of altered seed composition on vulnerability to disease. Objective 3, the improvement of drought tolerance, will identify QTLs for drought tolerance derived from exotic germplasm and test a rapid screening method that may streamline breeding for drought tolerance.
1b. Approach (from AD-416)
The research will be accomplished by combining conventional breeding technology with Quantitative Trait Loci (QTL) analysis and near isogenic line development. Drought tolerance is treated as a topic distinct from yield, because it is the greatest agronomic limitation to soybean production in the USA. Using molecular marker technology in combination with field and lab studies, we will assess the genetic potential of accessions in the USDA soybean germplasm collection for improving soybean yield potential, seed composition, disease resistance, and drought tolerance. We will identify the genomic location of alleles which govern these traits.
3. Progress Report
Soybean is among the least diverse crops in the USA. Such narrow genetic diversity renders a crop vulnerable to changing pests and environmental extremes, also limits the ability of breeders to improve the crop. New genetics are needed to address this diversity problem. This project will i) identify exotic germplasm in the soybean collection which carry key economic traits, ii) determine the genomic location of the genes governing these traits using DNA markers, and iii) use DNA markers and diverse breeding lines derived from exotic germplasm in practical crop improvement. The primary traits of interest, corresponding to the three objectives of this project, are improved seed yield, improved seed composition, and improved drought tolerance. Approximately 20,000 experimental yield plots were grown in pursuit of project objectives. Research was carried out at 5 diverse sites in North Carolina. To improve drought tolerance, more than 5000 yield plots were evaluated at a drought-prone field site. To improve yield using exotic germplasm, Quantitative Trait loci (QTL) populations and related advanced breeding lines carrying exotic pedigree were grown in more than 7000 yield plots. As a part of that effort, 7 USDA-ARS lines tracing to high-yielding exotic Japanese varieties were grown in 13 locations of the USDA Southern Uniform test VIII. Their average yield was 93% of the checks. Four new USDA-ARS lines tracing 25% ancestry to Japanese varieties were grown in the regional USB Southern Diversity Trials and outyielded the check by 3 bu /ac. For the first time, 14 lines with 50% exotic G. soja pedigree were included in this USB regional test. Yields were about 70% of the best check, but two lines yielded 100% of the N7103 G. max parent. Ten additional new lines with 25% of their pedigree tracing to Japanese varieties were tested in 2 NC environments and averaged 5 to 8 bu./ac better than the cultivar Young in each environment. The use of F2 bulk yield as a criterion for selection of superior breeding populations derived from exotic germplasm was evaluated. The F2 generations of 5 different bi-parental combinations were tested in field experiments. Percentages of mid-parent heterosis ranged from 2 to 13%. Further efforts to confirm the use of this method are in progress. To improve end use qualities of soybean (nutritional and value-added traits), quantitative-real time polymerase chain reaction assays were developed and verified to quantify the growth of the fungal pathogens Cercospora kikuchii causal agent of leaf blight and purple seed stain, and Diaporthe phaseolorum var. meridionalis, causal agent of southern stem canker and seed decay. Further efforts have produced q-RT PCR primers and assays to measure the expression of 15 defense genes and 4 reference genes in soybean leaves and seeds. A detached seed assay for pathogen inoculation studies was developed. The defense responses of soybean elicited in both leaves and detached seeds have been described in a manuscript submitted for publication.
1. Drought-tolerant germplasm developed. A new generation of breeding lines was developed and tested for drought response. In regional and local testing, two of them, N01-11136 and N01-11771, were slow wilting and showed a substantial yield benefit when grown under dry conditions. They also yielded reasonably well in good environments which had minimal stress conditions. These genetic materials have been made available to commercial breeders as parental stock.
2. QTLs for the canopy wilting trait reported. Two major QTL for soybean wilting were discovered. Drought tolerance is a very difficult for commercial breeders to select upon. These QTL offer a short cut method to facilitate use of drought tolerant germplasm in breeding without resort to development of drought field-testing sites.
3. Good yielding breeding lines developed from wild soybean (G.Soja). New breeding lines have been developed which trace 50% of their ancestry to the wild soybean. These lines yield approximately 70% of the best checks and 100 % of the max parent used to develop the breeding lines. This is an unprecedented success in the use of wild soybean in plant breeding. These new lines and the breeding methodology used to develop them will be a great new resource for the soybean industry.
4. A productive soybean line with increased stearic acid has been developed. The line, N08-2607, has a stearic acid content in seed oil of 11%, which is 3 fold greater than standard soybean oil. This line will be publicly released as a germplasm in the next year. A mutant SCAPD gene is responsible for this increase. Another high stearic mutant line, TCJWB03-806-7-19, has been developed. This mutation is at a different gene locus than the N08-2607 mutant. When the two genes are combined in a single line, stearic acid is increased to 17%. Stearic acid, unlike palmitic acid, is a saturated fatty acid that is not associated with increases in blood cholesterol and increased risk for coronary heart disease. A “heart healthy” high- stearic soybean oil will provide oil processors and food manufacturers with a saturated oil that can be used to replace high-palmitic tropical oils in margarines, shortenings, and food products that require shortening.
5. The effect of seed fatty acid content and seed defense gene expression on the growth in seeds of the fungal pathogens Cercospora kikuchii and Diaporthe phaseolorum var. meridionalis was investigated. ARS researchers at Raleigh, NC found that increased oleate in seeds grown at warmer temperatures was associated with higher expression of the stearoyl acyl carrier protein desaturase alleles GmSACPD-A/B, that seeds with higher oleate supported increased growth of C. kikuchii, while seeds with higher linoleate supported increased growth of D. phaseolorum, and that seeds produced at either a warm or a cool relative to normal temperature had, prior to inoculation, down-regulated PR1, PR3, PR4, and PR10 defense gene expression. Taken together, the data suggests that both the oleate and linoleate content and defense gene expression are likely key factors controlling the initial growth of these pathogens in infected soybean seeds.
Carter Jr, T.E., Rzewnicki, P.E., Burton, J.W., Villagarcia, M.R., Bowman, D.T., Taliercio, E.W., Kwanyuen, P. 2010. Registration of N6202 soybean germplasm with high protein, good yield potential, large seed and diverse pedigree. Journal of Plant Registrations. 4:73-79.