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ARS Home Midwest Area Urbana, Illinois Soybean/maize Germplasm, Pathology, and Genetics Research Research





- Clough, Steven
- 2023
- 2022
- Publications
- Plant Diseases (303)

Research Project: **Location:
                            Soybean/maize Germplasm, Pathology, and Genetics Research** Project Number: 5012-22000-023-000-D
                        
                        Project Type: In-House Appropriated Start Date: Apr 30, 2022
                        
                        End Date: Apr 29, 2027 **Objective:**
                        
                        Objective 1: Characterize emerging and endemic plant pathogens/pests used for identifying sources of resistance;
Objective 2: Identify and characterize resistance to pathogens/pests in Glycine species and map resistance loci to allow transfer into soybean;
Objective 3: Transfer putative resistance/defense alleles into elite soybean germplasm to validate effectiveness in reducing disease severity. **Approach:**
                        
                        The work will characterize two emerging soybean diseases and the pathogens that cause them (red crown rot by Calonectria ilicicola and red leaf blotch by Coniothyrium glycines), identify resistance against these two pathogens and root-knot nematode (Meloidogyne incognita), and transfer resistance into elite genetic material suitable for use in breeding programs. 

For red crown rot, lower stems of plants from fields in Illinois will be sampled (15-20 stems per 10-15 locations), isolates purified from infected tissue, and tested for virulence. For red leaf blotch, diseased leaf samples will be collected from soybean fields by our collaborator in Africa and purified isolates tested for virulence. The initial screening for red leaf blotch will use two isolates, one at Fort Detrick and one in Kenya. The goal for both pathogens is to recover 150 plus isolates for phenotyping and genotyping. Genetic characterization of C. ilicicola and C. glycines populations will be achieved through sequencing and using DNA single nucleotide polymorphisms marker analysis to estimate the parameters of genetic diversity and population structure and identify signatures of selection in these populations.

To evaluate resistance, experiments will be arranged in the following priority of testing: 1) released cultivars consisting of 25 public soybean cultivars, 2) a set of 70 ancestral lines, 3) a panel of 350 soybean plant introductions that have been identified as a genetically diverse core set, 4) a set of 100 G. soja accessions, and 5) a set of 200 accessions of perennial Glycine species. Having genotypic and phenotypic data on all accessions will allow for a genome wide association studies to identify resistance loci. 

The strategy for transferring resistance to breeder-friendly genotypes will be dependent on sources of resistance identified. Resistance in G. max and G. soja will be crossed to elite breeding material. If resistance is found only in perennial Glycine species, then intra and inter specific crosses and mapping will be made if possible. Resulting lines with partial resistance or specific resistance conditioned by single major genes will be selected. 

For root-knot resistance, we have F2:5 recombinant inbred lines (RILs) developed and resistant and susceptible G. latifolia accessions genotyped; preliminary mapping showed most of the resistance was controlled by a single locus on chromosome 13. We will do deep sequencing to continue to fine map this region until a small enough interval is identified to allow for prediction of candidate resistance genes. For phenotyping additional RILs, seeds will be scarified, pregerminated, and then planted in sand in polyvinyl tubes. Three weeks after transplanting, the seedlings will be inoculated with freshly prepared egg suspensions at a rate of 2,000 M. incognita eggs per plant. Candidate genes showing polymorphisms between resistant and susceptible accessions will be designed into Agrobacterium transformation vectors for transformation into susceptible G. max cultivar Williams 82. Lines homozygous for the transgene will be evaluated for resistance as described above.


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