Screened 280 ancestral lines for resistance or partial resistance to P. ultimum pv ultimum, P. irregulare (Duplicate runs of rice inoculum assay) and F. graminearum (Duplicate runs - rice inoculum and rolled towel assays). Association mapping of phenotypic data with genotypic detected no significant marker trait associations for partial resistance to F. graminearum. Population size and/or marker density combined with environmental error in measurement of traits resulted in insufficient power to detect significant marker-trait associations
Measures of resistance included reduced root necrosis score and maintenance of relative root weight and relative root length when inoculated plants are compared to uninoculated. Association mapping detected significant marker associated with reduced root necrosis, relative root weight and root length at a single position and multiple markers for maintenance of relative root dry weight.

As alternative approach to association mapping, six crosses were made between diverse sources, resistant and susceptible lines, for use in biparental mapping. Growout of seed from crosses (F1) will be conducted in South American location to make seed available for 2016 growing season.

Pinpointed location of RpsUN1 to a 6.5-cM region between two SSR markers, Satt159 and 03_0250, on chromosome 3 and RpsUN2 to a 3.0-cM region between 16_1275 and Sat_144 on chromosome 16. Haplotype analysis comparing this region between PI 567139B and other genotyped soybean accessions has identified RpsUN1 and RpsUN2 as unique and are present only in PI567139B.
Introgressed RpsUN1 and RpsUN2 into elite breeding lines.

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Minnesota
During this project year tests of multiple methods of inoculation with F. graminearum were conducted to validate the methodology, effectiveness, and consistency, to be used to conduct screening for resistance to seed, seedling, and root rot caused by F. graminearum. Based on these tests, the rolled towel assay and rice inoculum method were selected as the most reliable screening methods for assessing root rot and root development.

Utilizing these methods, rolled towel assay and rice inoculum methods, we completed phenotyping and association mapping of first and second runs of screening in 280 ancestral lines for resistance or partial resistance to P. sojae and F. graminearum.

Association mapping analysis was conducted on results obtained in P. sojae and F. graminearum phenotyping indicating the location of markers for partial resistance to F. graminearum. In 280 ancestral lines two categories of marker were identified that indicated resistance to F. graminearum, one marker identified on chromosome 8 indicating resistance to root necrosis and 10 markers associated with reduced susceptibility for reduction in root mass. These markers may also be good targets for genomic selection for root rot resistance. Association mapping of phenotypic data for P.sojae partial resistance did not detect significant marker train associations for resistance to P. sojae although phenotyping indicated that 280 lines differed widely in response to P.sojae inoculation. To examine this phenomenon more closely we have elected to examine the results of biparental crosses between cultivars exhibiting a wide divergence of responses to P.sojae inoculation. Completed six crosses of lines with divergent resistance characteristics, resistant and susceptible, for use in biparental mapping of resistance and partial resistance to P. sojae.

First run consisting of one rep of evaluation of 280 lines for resistance or partial resistance to P. ultimum is underway.


Purdue:
Generate a higher resolution genetic and physical map and finer mapping of these two genes, RpsUN1 and RpsUN2. RpsUN1 gene has been narrowed from an ~1,300-kb region to an ~150.8-kb region. RpsUN2 gene was narrowed from an ~ 64-kb region down to ~35.6-kb region.

Identify possible candidate genes in the interval region by quantitative real-time PCR gene expression and further analysis of candidate genes in the RpsUN1 and RpsUN2 regions. Expression data demonstrate that only a single gene Glyma.03g034600 in the RpsUN1 region showed enhanced expression pattern after inoculation with P. sojae race 17. By contrast, three genes Glyma.16g215200, Glyma.16g215000 and Glyma.16g214900, in the RpsUN2 region showed enhanced pattern in response to P. sojae race 25. These are candidates for further validation.

Crossed and backcrossed RpsUN1 and RpsUN2 donor lines with four Purdue elite lines, and got the three backcrossing introgression lines with RpsUN1 and RpsUN2 genes, respectively.