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EFFECT OF SOYBEAN CYST NEMATODE ON FUSARIUM
ROOT ROT OF SOYBEAN

EXECUTIVE SUMMARY
NORTH DAKOTA SOYBEAN COUNCIL
JUNE, 2017

Dr. Berlin D. Nelson Jr., Principal investigator, Plant Pathology, NDSU
Dr. Hui Yan, Research Scientist, Plant Pathology, NDSU

Furarium root rot caused by F. solani and F. tricinctum are two common and serious root rot pathogens of soybean in North Dakota. This disease occurs in both the seedling and adult stages. Although Fusarium is common on soybean plants, it does not always cause yield losses. Healthy, well growing plants can produce new roots and compensate for the loss of decayed roots. Plants are more likely to suffer from Fusarium root rot when there is a high amount of pathogen in the soil, and when plants are stressed by environmental factors such as a lack of water, high temperatures or biological factors such as presence of other pathogens. Soybean cyst nematode (SCN) is now common in many ND soybean fields. SCN causes wounds as they penetrate the roots and they change the physiology of the root while feeding. These effects of the nematode could increase the damage caused by Fusarium root rot. The goal of this research is to determine if the interaction of soybean cyst nematode with Fusarium root rot results in greater damage to the plant.

This research was initiated in June 2016 with a field experiment where soil was infested with F. solani and F. tricinctum alone or infested with both Fusarium and soybean cyst nematode at 5,000 eggs per 100 cc of soil. The SCN susceptible soybean Barnes was planted. Within three to four weeks most of the plants were dead or dying due to post-emergence damping off caused by both Fusarium species and surviving plants had such severe root rot that plants did not grow sufficiently to allow SCN to develop. Because of these results there were no significant effects from soybean cyst nematode in the field experiment. Similar but expanded experiments were conducted in the greenhouse with high and low inoculum levels of F. solani and F. tricinctum and several SCN egg levels. Emergence, plant height, root rot severity, root length, plant dry weight and root dry weight were measured over five weeks. There were similar trends in all experiments with generally lower measurements of plant growth associated with the addition of SCN to the soil when Fusarium was present, but not all differences between the two treatments were statistically significant. In some experiments with F. solani, the addition of SCN resulted in a significant reduction of plant height, dry weight, or a significant increase in root rot severity. In other experiments, the addition of SCN with F. tricinctum resulted in lower plant height, plant dry weight, root length and root dry weight compared to plants growing only with only F. tricinctum. These negative results on plant growth were usually greater with higher SCN egg levels.

In conclusion, at low levels of Fusarium inoculum and moderate to high egg levels of soybean cyst nematode, the interaction of these two pathogens can reduce plant growth and increase root rot severity. Because Fusarium root rot is common in this area, this data is another indication that the management of soybean cyst nematode should also focus on keeping egg levels low in infested fields to avoid interactions with soil borne fungal pathogens.