Synergism in the interaction of Fusarium virguliforme with Heterodera glycines in sudden death syndrome of soybean

Abstract

Sudden death syndrome (SDS) of soybean caused by Fusarium virguliforme has increased in geographical distribution in the North Central region of the U.S. The disease often co-occurs with the widely distributed Heterodera glycines. The extensiveness of the interaction of SDS and H. glycines at different soil moisture levels is not fully defined. Further, it is not clear if Meloidogyne spp., that recently is more frequently observed in soybean areas, forms a disease complex with F. virguliforme. In a multi-factor factorial-designed mi-croplot experiment, SDS symptoms and yield parameters were determined following infestation with F. virguliforme and either H. glycines or M. incognita at different soil moisture regimes in different microbial backgrounds rendered by soil fumigation. On soybean ‘Williams 82’, susceptible to the three pathogens, H. glycines increased severity of foliar symptoms of SDS irrespective of being naturally present or added to previously fumigated soil, while yield parameters declined in the plots co-infested with F. virguliforme. This increase was synergistic in some contexts as determined by Gowing’s formula. In pre-season-fumigated soil, only plants in plots concomitantly inoculated with H. glycines and F. virguliforme had more severe SDS than plots with no nematode or M. incognita amendment when the plots were heavily watered (P < 0.01). No synergism between F. virguliforme and M. incognita was detected. The results provided the conceptual framework of the synergistic interaction of H. glycines and F. virguliforme in a disease complex under different soil moisture conditions.