Location: Soybean and Nitrogen Fixation Research2011 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, and also limits the ability of breeders to improve the crop. New genetics are needed to address 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. Research was carried out at 5 diverse sites in North Carolina. 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, 15 USDA-ARS lines tracing pedigree to high-yielding exotic Japanese varieties were grown across the South in USDA Southern Uniform Yield Trials. Thirty-two USDA-ARS breeding lines tracing at least 25% ancestry to Japanese varieties were grown in the regional United Soybean Board (USB) Southern Diversity Trials. Many of these new breeding lines outyield the standard check varieties. Started a Marker Assisted Backcrossing program to introgress two high oleic genes into advanced soybean breeding lines adapted to North Carolina. These genes (FAD2-1A and FAD2- 1B), when present together in a genotype, are able to produce soybean seed oil with greater than 70 percent oleic acid. The first backcross generation is now being propagated in North Carolina. Sequenced SACPD A, B and C genes in all of our genotypes which have high stearic oil and identified a potentially useful single nucleotide polymorphism (SNP) molecular marker in SACPD-B. This fall we will genotype and phenotype a population that is segregating for this SNP to determine if there is association between the molecular marker and the trait. A detached soybean seed assay using green, immature seeds harvested 35 days after flowering was optimized in order to study fungal seed colonization and host defense gene expression. Quantitative real time, reverse transcription polymerase chain reaction (qRT-PCR) technology was optimized to measure the expression of 15 seed defense genes, three reference genes, and the accumulation two fungal pathogens in inoculated seed tissue. A manuscript describing an analysis comparing defense gene expression in infected soybean leaves and seeds was published. Experiments to investigate the effects of temperature treatments during seed development on defense gene expression and pathogen colonization in seeds was completed. To improve drought tolerance, more than 5000 yield plots were evaluated at a drought-prone field site. From this work, 10 advanced breeding lines derived from exotic Asian germplasm were submitted toregional testing trials. DNA extraction and SNP analysis are in process for three QTL populations.
1. Drought-tolerant germplasm N05-7432 developed. Most U.S. soybean varieties are sensitive to drought. This exciting new slow-wilting drought-tolerant material is a clear exception to that trend. In 3 years of regional testing over 25 environments, ARS researchers at Raleigh, NC, showed that this drought tolerant line performs on a par with elite check cultivars when yield levels are high (greater than 55 bu./ac.). At lower yield levels, this new type yields more than 5 bu./ac. better than leading varieties. Its pedigree is unique in that it traces to two drought tolerant plant introductions maintained in the USDA soybean germplasm collection. This is an unprecedented success in drought tolerance breeding. This genetic material has been made available to commercial breeders as parental stock.
2. High-yielding genetically-diverse breeding lines developed from Japanese soybean varieties. The genetic base of US soybean is too narrow and threatens to curb breeding progress in the USA. ARS researchers at Raleigh, NC, are using the rich genetic diversity of the USDA germplasm collection to combat this problem. Recent developments clearly indicate that this approach works; recent seed-yield breakthroughs in the project are directly connected to the use of exotic Japanese soybean varieties as breeding stock. New breeding lines have been developed which trace 25% of their ancestry to these Japanese stocks and yield 10% better than the appropriate US check varieties. These results clearly show that Japanese yield enhancing genes from the USDA germplasm collection are poised to rectify important production problems that threaten U.S. agriculture. This is an unprecedented success in the use of exotic 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.
3. High temperature during soybean seed development reduces seed defense gene expression and increases seed colonization by fungal pathogens. ARS researchers at Raleigh, NC, found that in addition to altering seed fatty acid composition, temperature also altered seed defense gene expression and pathogen colonization after seeds were infected. Development of seeds exposed to a higher (34/26 degrees C day/night) temperature produced significantly lower levels of defense-related gene expression in seeds and increased colonization of seeds by the purple seed stain pathogen, Cercospora kikuchii, than seeds exposed to a lower (26/22 degrees C day/night) temperature. Results suggest a rationale by which global climate change might worsen plant-pathogen interactions and potentially crop productivity.
4. Development of new high oil soybean germplasm, NC Miller. Soybean is the most important oil crop in the USA. ARS researchers at Raleigh, NC, have developed a new maturity group V germplasm, NC Miller, which is high yielding and has higher oil content than the typical cultivars (21.6% oil content)now grown by farmers. This non-GMO germplasm provides an alternative to growers who are interested in organic soybean production and can also be desirable as parental stock in development of new cultivars.Upchurch, R.G. and Ramirez, M.E. 2010. Defense-related gene expression in soybean leaves and seeds inoculated with Cercospora kikuchii and Diaporthe phaseolorum var. meriodinales. Physiological and Molecular Plant Pathology. 75:64-70.