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Terry L. Niblack Terry L. Niblack
Professor of Soybean Cyst
Nematode Management
Department of Crop Sciences
(217) 244-5940
tniblack@illinois.edu

Most SCN-Resistant Soybean Varieties Are NOT Resistant to SCN. 2005 Update on SCN Races in Illinois.

Yes, you read the title right: no matter what the seed label says, most soybean cyst nematode (SCN)-resistant soybean varieties are NOT resistant to SCN. At least, not to the SCN populations we have in Illinois.

How can this be? The nematodes have changed.

The last time there was a good survey of SCN races1 in Illinois was in 1989-902. Back then, 88 of 102 counties contained one or more fields known to be infested with SCN. The results of the survey showed that 64% of the SCN populations in Illinois were classified as race 3. That meant, basically, that nearly two-thirds of the SCN in Illinois could not attack any known resistant varieties.

What about the one-third that could attack resistant varieties? These were classified as races 1, 2, 4, and 5. And although this sounds like many SCN populations were able to attack and damage resistant varieties, actually most of them would be classified as "weak" today. In fact, only one SCN population (from Grundy County) was a "strong" race 1 that could be expected to damage race 3-resistant soybean.

What has happened in the last 15 years?

But, just because these SCN populations can attack resistant varieties doesn't necessarily mean they can reduce soybean yield. That depends on three other factors:

How can you make sure the varieties you're using ARE resistant to SCN? The following recommendations correspond to the three factors listed in the paragraph above:

figure 1

Figure 1: In 2004, over 630 SCN-resistant varieties were tested for their levels of resistance to an SCN population representing a common type in Illinois (type 2, or old race 1). We found that most varieties were not resistant to this type, and therefore not resistant to most SCN populations in Illinois. HR = highly resistant; R = resistant; MR = moderately resistant; LR = low resistance; and NR = no effective resistance.

1As you know, we don't talk about races in Illinois anymore. For further information on why, see Niblack et al., 2002. A revised classification scheme for genetically diverse populations of Heterodera glycines. Journal of Nematology 34:279-288. Available online at http://palmm.fcla.edu/nematode/.

2 For further information, see Sikora, E., and Noel, G. R. 1991. Distribution of Heterodera glycines races in Illinois. Supplement to Journal of Nematology 23:624-628. Available online at http://palmm.fcla.edu/nematode/.

 
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