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ARS Home » Midwest Area » Urbana, Illinois » Soybean/maize Germplasm, Pathology, and Genetics Research » Research » Publications at this Location » Publication #180951
Title: THE ILLINOIS SCN TYPE TEST: PRACTICAL APPLICATION OF THE HG TYPE CLASSIFICATION SYSTEM

Author
item NIBLACK, TERRY - UNIV OF ILLINOIS
item NOEL, GREGORY
item BOND, JASON - UNIV OF ILLINOIS

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/2/2005
Publication Date: 3/2/2005
Citation: Niblack, T.L., Noel, G.R., Bond, J. 2005. The Illinois SCN type test: practical application of the HG type classification system. Proceedings of Southern Soybean Disease Workers. p. 14.

Interpretive Summary:

Technical Abstract: The HG Type classification system for soybean cyst nematode (SCN) populations is based on the female index, a measure of SCN virulence relative to the susceptible soybean cultivar Lee 74, on seven soybean plant introductions (PI): 1) 548402 (Peking); 2) 88788; 3) 90763; 4) 437654; 5) 209332; 6) 89772; and 7) 548316 (Cloud). These seven lines represent the sources of resistance that have been used to develop SCN-resistant cultivars in the United States, according to their publication in the journal Crop Science. Although still a bioassay and subject to difficulties associated with testing living organisms, the HG Type test avoids some of the problems inherent in the race classification scheme. One of these problems was the difficulty of adapting the test for different regions or countries, and interpreting the results. Another was the confusion that resulted when cultivars labeled as “resistant to race 3,” for example, were found to be susceptible to particular SCN populations identified as race 3. We have been working with the HG Type system to address these problems. Of the seven indicator lines, only three have been used to develop SCN-resistant soybean cultivars currently available in Illinois: PI 548402, PI 88788, and PI 437654 (indicator lines 1, 2, and 4). An incomplete HG Type test named the Illinois SCN Type test includes only these three indicator lines and Lee 74, and may include one or more additional cultivars for comparison. Conditions of the test are as specified for HG Type tests, except that it may be conducted in a hydroponic system so that labs without greenhouse facilities are able to perform it after training. The results can be used in conjunction with data from yield trials, SCN-resistance screening, and lists of sources of resistance to aid cultivar selection decisions. Similar adaptations can be made for use in other regions and other countries, where different sources of resistance may be used. Using the HG Type test, we have determined that the most common HG Types in Illinois are 0, 7, and 2.5.7. HG Type 0 populations are not virulent on any of the 7 sources of resistance, and HG Type 7 is virulent only on PI548316. HG Types 0 and 7 would both formerly have been called races 3 or 6 (not respectively). HG Type 2.5.7, virulent on PI88788, 209332, and 548316, would formerly have been called race 1 or 5. Because different SCN populations of the same type can differ widely, we screen cultivars labeled as “SCN resistant” to five different SCN populations, three of which are HG Type 0 or 7, and two HG Type 2.5.7, originating in different parts of Illinois to represent the types we find there. From 2001 to 2004, we screened all of the SCN-resistant cultivars entered in the Illinois State Variety Trials (636 in 2004) to all five SCN populations. Three years’ data have verified that SCN virulence on a particular source of resistance predicts virulence on cultivars derived from that source, but the cultivars themselves vary widely in their response to infection. In addition, up to half of the cultivars labeled “SCN resistant” are actually susceptible to our HG Type 0 or 7 populations. Combination of the Illinois SCN Type test and the SCN-resistance screening program has improved our ability to give reliable recommendations to soybean farmers in Illinois.