Effect of F. Virguliforme and H. Glycines On Soybean.

Fusarium virguliforme, the soilborne fungus which causes sudden death syndrome (SDS) of soybean, and Heterodera glycines Ichinohe, soybean cyst nematode (SCN), are two economically important pathogens in the Midwest. The pathogens are often found together in soybean (Glycine max (L.) Merr.) fields. This study was conducted to determine the effect genotype, F. virguliforme populations, and H. glycines populations have on yield and to examine the interaction between the two pathogens. In 2008 and 2009, four genotypes with different levels of resistance to SDS and H. glycines were planted at seven environments. F. virguliforme and H. glycines soil populations were quantified at planting, midseason and harvest. At the end of the growing season, area under the disease progress curve, F. virguliforme root population, and H. glycines reproductive index were determined and plots harvested for seed yield. Soil populations of F. virguliforme and H. glycines at planting, harvest, and midseason varied across environments. Within environments, generally, they were not significantly different. Genotype performance in seed yield varied within and across environments. As disease pressure increased, the performance of resistant genotypes increased compared to genotypes varieties. Genotypes resistant to SDS yielded higher than susceptible genotypes. There were negative correlations between yield and disease rating and F. virguliforme soil population at planting. F. virguliforme soil populations at planting and midseason were positively correlated to H. glycines populations at planting. Resistance to SDS and H. glycines is important in protecting yields in fields with a history of the two diseases. This information will improve decisions regarding cultivar selection to minimize losses to SDS and H. glycines.