Iowa fields are commonly infested with both SCN and brown stem rot (BSR). In the early 1990s, researchers observed that BSR-resistant soybean varieties had much greater than expected levels of BSR disease in fields infested with SCN than in those without SCN.
Research was initiated in the mid 1990s to study how SCN affects the fungus that causes BSR (Phialophora gregata, now sometimes called Cadophora gregata) and how the nematode affects BSR disease symptom development, infection and colonization by the BSR fungus, and soybean yield.
Key findings from the work are:
- In BSR-resistant soybean varieties, SCN infection resulted in significant increases in severity of the internal stem discoloration symptoms caused by the BSR fungus.
- SCN infection resulted in earlier infection and more widespread colonization by the BSR fungus in BSR-resistant soybean varieties.
- SCN increased BSR disease symptom development, and infection and colonization by the BSR fungus even in varieties with both BSR resistance and SCN resistance.
- The higher the SCN population, the greater the effect of SCN on BSR disease symptom development, and on infection and colonization by the BSR fungus.
Most of the research described above was done with the common genetic type of the BSR fungus, called “genotype A”. In 2000, another genetic type of the BSR fungus, genotype B, was reported. Genotype B causes no foliar disease symptoms and much less internal stem discoloration than genotype A. Research now is focusing on determining how SCN interacts with genotype B of the BSR fungus to affect BSR disease and yield loss.