Iowa State University has released two newly updated resources to help soybean growers (and crop consultants who advise farmers) fight soybean cyst nematode.
The first publication is an updated version of the annual ISU Extension publication Soybean cyst nematode-resistant soybean varieties for Iowa, Pm-1649. It's available from ISU Extension publications online or from your county Extension office. "This is the most recent compilation of information on SCN-resistant soybean varieties in maturity groups zero, 1, 2 and 3 available for Iowa growers," says Greg Tylka, ISU Extension nematologist and plant pathologist.
Some points to note about the information contained in this publication:
* There are 763 soybean varieties listed in the publication. That's a record high number for this annual publication—which dates back to 1991. There were 743 varieties in the list compiled at the end of 2006.
* Only 16 varieties in the current list have a specific resistance source listed other than PI88788—that's just 2% of the 763 varieties.
* There's only one CystX variety in maturity group zero/1 and only one such variety in maturity group 2 (both from Latham) in the current list.
* There are 11 varieties with Peking as the listed source of SCN resistance in the current list.
* There's one variety with Peking/PI88788 as the listed source of resistance in the current list.
* There are three varieties with Hartwig/Peking listed as the source of resistance in the current list.
* None of the maturity group 3 SCN-resistant varieties have anything other than PI88788 as the source of resistance.
Second new SCN publication also helpful
Another new publication from ISU Extension lists the results of Iowa State's SCN-resistant Soybean Variety Trial program for 2007. "This one is different from the other publication," says Tylka. "This one that lists and explains our SCN-resistant soybean variety trial results for 2007 is publication number IPM 52, revised January 2008."
The ISU variety trial results publication contains results of field testing of SCN-resistant soybean varieties entered in ISU tests at 10 locations throughout Iowa in 2007. Individual location results from the ISU SCN-resistant Soybean Variety Trial program have been available online since December and all results are now posted there.
Tylka lists some noteworthy points about these results:
* Three locations in 2007 ended up not being very useful because of low initial SCN population densities. Those locations were Council Bluffs, Manchester and Crawfordsville.
* The Vincent location in 2007 had an SCN population with greater than 10% reproduction on PI88788 in the HG type test (13.4%) and 0.1% reproduction on Peking. Sure enough, the top 2 yielding soybean varieties (and 3 of the top 4) at that location were varieties with SCN resistance derived from Peking. See the pages numbered 6 to 7 in the file online for results at the Vincent location.
* At the Cambridge location in 2007, the SCN population had 24.3% reproduction on PI88788 and 0.1% reproduction on Peking in the greenhouse HG type test, but the lone SCN-resistant soybean variety with Peking as the source of resistance at this location (Pioneer 93M53) finished in the middle of the pack for yield. The top 3 yielding SCN-resistant varieties (each with PI88788 as the source of resistance) averaged 65 bushels per acre. That's 10 bushels per acre more than the three top-yielding susceptible varieties shown at the bottom of the graphs and the tables. See pages 14 and 15 in the online publication for results from the Cambridge location.
* At the Mason City location in 2007, the SCN population in the field had less than 10% reproduction on PI8878 and Peking in the greenhouse HG type test, and the top two yielding SCN-resistant varieties had resistance from Peking. See pages numbered 8 and 9 in the online file for the Mason City location results.
So what does Tylka think the results from Vincent, Mason City and Cambridge tell researchers and farmers? He says, "The results indicate that the HG type or race—if you still refer to it as race—of SCN population in a field is an important predictor of yield for SCN-resistant soybean varieties growing in SCN-infested fields—unless it is not. What I mean is that the results tell us that yield of SCN-resistant varieties growing in SCN-infested fields is not just about the HG type of the SCN population in the field and the source of resistance in the soybean variety grown—it's just not that simple."