Sources of resistance, effect of maturity groups and marker-trait associations associated with Fusarium graminearum causing root rot of soybean (Glycine max)

Fusarium graminearum Schwabe is an important fungus causing root rot of soybean (Glycine max L.) in the United States. In this study, 248 accessions (including the susceptible check, ‘Williams 82’) from the USDA germplasm collection (MG 0 to V) were screened with a single isolate of F. graminearum using the inoculum layer inoculation method in the greenhouse to identify resistant parental materials. Disease severity was evaluated 21 days post-inoculation on a 1-to-5 rating scale and expressed as relative treatment effects (RTE). Eight accessions (PI437949, PI438292, PI612761A, PI438094B, PI567301B, PI408309, PI361090, and P188788) had significantly lower RTE when compared to ‘Williams 82’ based on 95% confidence intervals. Further, the effect of maturity groups (MG) was assessed on disease severity, and accessions belonging to MG 0 or I had significantly greater RTE than cultivars belonging to MGs II to V based on 95% confidence intervals. A genome-wide association study analysis was conducted using 42,079 single nucleotide markers and six marker-trait associations were identified that may be novel sources of F. graminearum resistance. The identification of new resistant parental materials and MTAs associated with resistance to F. graminearum will be useful in breeding programs for developing resistant cultivars.