Location: Soybean/maize Germplasm, Pathology, and Genetics Research
2017 Annual Report
Objectives
Objective 1. Relate the spatial and temporal dynamics of soybean pathogens, pests, and associated microbial communities to soybean productivity. Subobjective 1.A. Determine if novel virulent or resistance-breaking soybean pathogens/pests have emerged within the U.S. and other parts of the world. Subobjective 1.B. Determine the impact of selected biocontrol and beneficial microbes to reduce the impact of soybean pathogens and pests. Subobjective 1.C. Characterize variability and shifts in the pathogenicity of Phakopsora pachyrhizi populations in the southern U.S. to guide breeding program decisions.
Objective 2: Identify, characterize, and develop improved resistance in soybean that can be used for sustainable disease management strategies that include effective host resistance and biological control. Subobjective 2.A. Identify or characterize pathogen/pest resistance using annual and perennial accessions from the USDA Soybean Germplasm Collection and selected breeding lines. Subobjective 2.B. Develop agronomically competitive soybean breeding lines with disease- or pest-resistance genes from adapted or unadapted germplasm accessions in the USDA Soybean Germplasm Collection. Subobjective 2.C. Investigate relationships between soybean yields and resistance to soybean cyst nematode and Phytophthora sojae in public breeding lines from the Northern Uniform/Preliminary Soybean Tests.
Approach
The distribution and abundance of soybean pathogens and pests will be monitored on multiple geographic scales using pathogen-specific and metagenomic assays. The impacts of beneficial and insect-borne microbes on soybean diseases and yields will be characterized in replicated trials over multiple years. Changes in pathogen virulence over time will be assessed using soybean lines expressing different pathogen resistance genes and pathogen populations collected from soybean fields each year. New sources of resistance to pathogens and pests will be identified and characterized in cultivated soybean and related annual and perennial accessions from the USDA Soybean Germplasm Collection through field and greenhouse evaluations. Regions of soybean chromosomes associated with pathogen/pest resistance will be identified using phenotypic assays and molecular marker analyses of derived mapping populations. Soybean lines shown to be resistant to soybean pathogens/pests will be used to produce breeding lines with enhanced resistance using phenotypic and marker-assisted selection techniques as appropriate.
Progress Report
Objective 1: Relate the spatial and temporal dynamics of soybean pathogens, pests, and associated microbial communities to soybean productivity. Research on developing models to examine movement of soybean rust spores was completed. Collections of pests from suction traps was complete up to 6/30/2017. Soybean leaf samples will be collected from production fields in 12 Illinois counties to assess the prevalence of soybean pathogens.
Objective 2: Identify, characterize, and develop improved resistance in soybean that can be used for sustainable disease management strategies that include effective host resistance and biological control. Field plots for evaluating diseases including Pythium root rot, Rhizoctonia root rot, Soybean vein necrosis, and sudden death syndrome were planted and inoculated. Some backcrosses for resistance to soybean aphids and to Phytophthora root and stem rot to elite soybean lines were completed. Propagation of a population of Glycine tomentella plants segregating for resistance to soybean sudden death syndrome was initiated for preparation of recombinant inbred lines. Soybean plants were inoculated with Soybean mosaic virus expression vectors to evaluate virus-based overexpression as a strategy to confirm biological functions of candidate genes predicted by QTL analysis and GWAS. One hundred and two (102) major ancestors of American public soybean cultivars developed prior to 1989 were screened for their responses to Pythium spp., resulting in the identification of 14 ancestral lines with partial resistance to an Illinois isolate of P. ultimum var. ultimum in greenhouse assays. Four of the most resistant lines were found to also be resistant to isolates of P. irregulare and P. sylvalticum. One-hundred forty-eight F1 seeds from crosses of different germplasm accessions and 6,160 breeding lines were planted in the field for agronomic and disease resistance evaluation. Selected lines and seeds harvested from selected plants will be advanced for further field testing and/or screened for resistance to pathogens in greenhouse assays.
Accomplishments
1. Identified accessions of wild perennial Glycine relatives of soybean with high levels of resistance to multiple populations of soybean cyst nematode (SCN). Soybean cyst nematode is a widely occurring and damaging pathogen that limits soybean production. Developing resistant cultivars is the most cost-effective method for managing this pathogen. Genes conferring resistance to SCN in soybean have been identified; however, there are SCN populations that overcome the most commonly used resistance genes. ARS scientists at Urbana, Illinois, cooperated with University of Illinois researchers to evaluate 223 plant introductions (PIs) of G. tomentella and 59 PIs of 12 other perennial Glycine species for responses to three SCN types, and a subset of 36 PIs to a fourth SCN type that overcomes all the resistance genes in soybean. Of the 223 G. tomentella PIs evaluated, 86 were resistant to three SCN types, 69 were resistant to two SCN types, and 22 were resistant to one SCN type. Of the other 12 perennial Glycine species, all PIs of G. argyrea and G. pescadrensis were resistant to all three SCN types. Of the 36 PIs challenged with the fourth SCN type, 35 were resistant, with 16 showing no cyst reproduction. Our study confirms that there are high levels of resistance to SCN among the wild perennial Glycine species. This represents an untapped resource for use in genetic studies and for improving resistance to SCN in soybean.
