Monday, August 9, 2010

Monitor resistant varieties for successful soybean cyst nematode management

Soybean cyst nematode (SCN), a small parasitic roundworm that attacks the roots of soybeans, is managed by crop rotation and growing SCN-resistant soybean varieties, yet it continues to be a significant threat to Minnesota soybean production.
University of Minnesota researchers are developing tools to maintain the productivity of SCN-resistant soybeans. SCN-resistant varieties are now widely grown in areas with SCN infestations and have dramatically improved yields. However, effective long-term SCN management will require wise use of the resistant varieties. The continued use of varieties with a single type of SCN resistance is likely to lead to genetic shifts in SCN populations. Most of the SCN-resistant varieties grown in Minnesota use the PI88788 resistance source with much fewer PI548402 (Peking) resistance-source varieties available. As a result of this selection pressure it should not be unexpected that SCN populations poorly controlled by resistant varieties have been in the state.  
A recent University of Minnesota survey found 67 percent of randomly sampled SCN populations could reproduce on resistance source PI88788 and 26 percent could reproduce on Peking resistance-source varieties—more disconcerting were several fields in which SCN could reproduce on soybean varieties of both resistance sources.
Public and private soybean breeding programs continue to find and incorporate new sources of SCN resistance to high-yielding varieties. Each year, University of Minnesota researchers evaluate these soybean varieties. Evaluations represent several maturity zones and SCN Hg types. Hg types ("Hg" stands for Heterodera glycines, the scientific name for SCN) are used to characterize which, if any, resistance sources can be attacked by a SCN population. These evaluations help producers select varieties that will perform well in their fields in the presence of ever-adapting nematodes. 
Soybean growers should be on the lookout for symptoms of injury to resistant soybeans. Stunted soybeans, potassium deficiency symptoms or yellowing of soybean top growth are clues that nematodes could be attacking soybean root systems. SCN symptoms in a field of resistant soybeans are an indication that it's time to make management changes.
University of Minnesota researchers are developing tools to maintain the productivity of SCN-resistant soybeans. Working in partnership with Minnesota Soybean Grower county association variety trials, University of Minnesota researchers are currently working to develop methods that soybean producers can use to detect developing resistance problems in their fields. 
For more information, visit the collaborative "Just for Growers: Minnesota Soybean Production" website at - 
By Bruce Potter, University of Minnesota Extension

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