Objective 1.
Lines segregating for SDS resistance derived from E07080 were evaluated for resistance reactions in a SDS disease nursery in Michigan. The 320 lines were split into two groups and the first 153 lines were used to map resistance genes and the second 167 lines were used to validate genes mapped in the first group. The 153 lines from the first group were genotyped with 5,361 genetic markers. Analyses of the SDS resistance of lines together with the marker data resulted in the identification of SDS resistance genes on six chromosomes. These newly identified genes will be useful in breeding new SDS resistant varieties.

Using the results from 2014 tests, MSU has started fine mapping of resistance genes from the two resistance sources. This is being done by phenotyping plants with recombination in the genetic regions where the SDS resistance genes are located. To ensure reliable phenotyping, susceptible and resistant checks were planted close to each plant to monitor the pathogen distribution in the disease nursery. Both the genotype and phenotype from each plant in every heterozygous line were collected and used for the subsequent analysis which is still ongoing.

Minnesota screened a population developed by crossing the parents Minsoy X Noir 1 for SDS root and leaf symptoms in a greenhouse. In this population, the genetic locations of two resistance genes were identified for root resistance and seven genes for foliar resistance. The seven genes for foliar resistance together explained 79% of the phenotypic variation for these symptoms. These greenhouse tests were done because two years of field tests were unsuccessful due to hail damage and deer feeding.

Objective 2
During 2014 and 2015, populations of near isogenic lines (NILs) were tested in multiple field environments in Illinois and Michigan through collaborations with UIUC, USDA-ARS, SIU, and MSU. These populations had been developed through backcrossing previously mapped SDS resistance genes into various genetic backgrounds and experimental lines within the populations were segregating for the resistance genes of interest. During 2014, we were able to confirm SDS resistance genes on chr 17, 10 and 1 in the confirmation tests. In 2015, none of the genes were confirmed. The inconsistent results from these studies show the need to conducting multi-year, multi-location trials to evaluate SDS resistance.

Objective 3
During the past year, RNA-Seq technology was used to assess the gene expression of soybean roots and leaves in response to the infection by Fusarium virgulifome, the causal agent of SDS. Using bioinformatics tools, 2490 differentially expressed genes were identified between infected and non-infected tissues (control) of NILs. Data analysis between leaves and roots showed that some genes are uniquely expressed in particular tissues. While genes involved in signaling such as hormone signaling pathways are induced in roots, other genes involved in reducing the toxin damage are induced in leaves reflecting different resistance mechanisms.