Effect of Soybean Cultivars Moderately Resistant to Soybean Cyst Nematode on SCN Populations and Yield

Spread of soybean cyst nematode Heterodera glycines (SCN) to much of the soybean (Glycine max) growing region in the Midwest has created a persistent and significant annual yield loss for soybean. Host resistance has been the primary means of reducing yield loss to SCN. It is not known how moderately resistant cultivars fit into the management of SCN. Moderately resistant cultivars can have high yield potential, but nematode reproduction is greater than on resistant cultivars. Moderate resistance is defined by a SCN female index (FI) of 10 to 29 in standardized tests, whereas cultivars with an FI < 10 are considered resistant. Two each of SCN-resistant, moderately resistant, and susceptible (FI > 60) cultivars were planted in the same plots for two soybean crops in annual rotation with corn. The SCN population was reduced 80 and 54% by resistant and moderately resistant cultivars, respectively, and increased 189% by the susceptible. Yields of the resistant and moderately resistant were 8.2 and 11.8 bu/acre better, respectively, than for the susceptible. All plots were planted to a susceptible cultivar in the final year of the study, and demonstrated there was a carry-over effect from previous cultivars. Following resistant and moderately resistant cultivars, yields of the susceptible were 6.6 and 4.3 bu/acre above following susceptible cultivars. This study showed that moderately resistant soybean cultivars can be an effective tool for improving profitability of soybean. Accepted for publication 9 April 2008. Published 18 June 2008.