Fusarium root rot of soybean—occurrence, impact, and relationship with soybean cyst nematode
Diaz Arias, Mercedes
Fusarium species are ubiquitous soilborne pathogens that can cause devastating and difficult-to-manage damping-off, root rot, wilt, or sudden death syndrome (SDS) in soybeans (Armstrong, 1950; French and Kennedy, 1963; Rupe, 1989). At least 12 different species of Fusarium have been reported to be associated with soybean roots (McGee, 1992); among these species and the diseases they cause, the economic impact is widely recognized only for SDS; economic impacts of Fusarium wilt and root rot are much less well documented. Fusarium root rot is widespread in US (Yang and Feng, 2001). F. oxysporum complex and F. solani complex are generally believed to be the major species causing root rot symptoms (Nelson, 1999), but other species may be pathogenic. These Fusarium species are not well identified and no comprehensive evaluations of their impact on yield have been undertaken, and their pathogenic capabilities are extremely variable. These knowledge gaps seriously hinder efforts to manage the diseases effectively. Observations suggest that there are interactions among Fusarium root rot and soybean cyst nematode (Heterodera glycines) (Nelson, 1999), but these interactions have not been verified or measured. The variable nature of Fusarium root rot occurrence may be better explained through more detailed knowledge of the important species and clarification of the importance of SCN-Fusarium interactions. Understanding this variability is an important step toward effective management of the disease.