Maturity Group Effect On Sudden Death Syndrome Foliar Symptom Severity in Iowa.

Sudden death syndrome (SDS) of soybean, caused by Fusarium virguliforme, causes significant yield losses in Iowa each year. The disease causes both root and foliar symptoms; foliar symptoms may develop as early as flowering, although onset is independent of the reproductive age of the plant. The relationship between disease development and plant growth stage may have an effect on severity of yield loss. Currently, cultivar selection is the most efficient way to manage SDS; however no information exists regarding maturity group and its effect on SDS in Iowa. Our hypothesis was that soybean cultivars belonging to earlier maturity groups will experience lower incidence, severity, and yield loss from SDS than later maturing cultivars. The objective was to evaluate differences in SDS foliar symptom severity and soybean yield among cultivars of earlier, optimum, and later maturity groups in Iowa. Experiments were conducted at two locations with a history of SDS. The experimental design was a randomized complete block in a split plot arrangement with four replications. The main plot consisted of three maturity groups with the sub plot consisting of a factorial combination of four cultivars within each maturity group (two resistant and two susceptible to SDS) and with and without SDS inoculum. Flooding in 2008 caused variable plant development and may have influenced the results. There was no effect of SDS inoculum on SDS severity. Yield was negatively correlated with disease severity; the optimum and later maturing soybean cultivars had the highest yields and averaged 417 kg ha^-1 more than the earlier maturing soybean cultivars. Consistently, resistant cultivars demonstrated lower disease severity than susceptible cultivars with the highest disease severity observed for early maturing susceptible cultivars. Research will continue in 2009 and data from both years will be presented.