The soybean cyst nematode (SCN), Heterodera glycines, is a small, plant-parasitic roundworm that attacks the roots of soybeans. It is considered the most destructive pathogen of soybean, causing incredible yield losses each year. Most plant-parasitic nematodes can be observed only with magnification, but the adult females and cysts of SCN are visible to the unaided eye.
SCN can cause yield loss almost at any population density, but it often does not cause obvious symptoms, such as stunting or yellowing, until it reaches high numbers. Consequently growers and agronomists are strongly encouraged to collect soil samples to determine if SCN is present in a field. In the last 10 years, we discovered that there is a consistent, strong, positive correlation between increasing SCN population densities and increasing soil pH, so high pH spots in fields are good places to first look for the presence of SCN. The basis of the correlation between SCN population densities and soil pH is not currently known and the relationship is unusual and interesting. SCN reproduction is usually less on plants suffering from diseases and other production problems, and soybeans growing in areas of high soil pH often are stunted and yellow due to iron deficiency chlorosis caused indirectly by the high soil pH.
Additional research in the laboratory, in collaboration with other scientists, is defining the interactions of SCN with other soybean diseases and insect pests. We are studying interactions of H. glycines with the soybean brown stem rot (BSR) fungus, Cadophora gregata, and have discovered that SCN causes more rapid and greater infection by the fungus and more frequent and severe disease symptoms. Also, soybean varieties that are resistant to the BSR disease lose their resistance when they are infected with SCN.
Research also is underway in the laboratory to determine how SCN interacts with the soybean aphid, Aphis glycines, to affect the reproduction of the two pests as well as soybean growth and yield.