Soybean genotypes will be evaluated for resistance to soybean cyst nematode (SCN), Heterodera glycines, by growing the plants in infested soil-sand mix for approximately 30 days, after which the numbers of adult SCN females and cysts on the roots will be assessed. Subsequently, the reaction of individual plants of each soybean genotype to SCN will be classified based on the criteria presented by D.P. Schmitt and G. Shannon in "Differentiating Soybean Responses to Heterodera glycines races", 1992, Crop Science 32(1):275-277.
Two or three seeds of each soybean genotype to be evaluated will be planted directly into individual replicate cone-tainers filled with soil-sand mix infested with Race 3 SCN/HG Type 0 (or selected other SCN populations if desired and available); a minimum of five replicates per genotype is recommended. Additionally, three seeds of Lee, PI548402, PI88788, PI90763, PI437654, PI209332, PI89772, PI548316, PI438489B, and Pickett (the HG Type and race differential genotypes) will be planted into separate replicate cone-tainers filled with the same SCN-infested soil-sand mix. All cone-tainers will be placed in an arbitrarily determined position in a greenhouse waterbath and incubated at constant 27oC under natural lighting conditions. Cone-tainers initially will be observed every day, and the second and third seedlings that emerge within each cone-tainer will be removed. Consequently, only the first seedling that emerges in each cone-tainer will be used in the evaluation. After approximately 30 days, the number of females and cysts on each soybean root will be determined by direct visual observation, and each replicate plant of each genotype will be classified into categories based on the number of females and cysts formed on the genotypes relative to the number formed on Lee or Lee74, which are considered by most soybean breeders to be universal SCN-susceptible soybean genotypes. An HG Type/Race test will be conducted to confirm the HG Type/Race of SCN population used in the screen. The unused seed of the soybean genotypes will be returned to the client with the report of the results or will be destroyed at the end of the experiment, whichever the client desires.
If time and greenhouse space permit, the staff of the Tylka Nematology Laboratory will perform greenhouse screening for SCN resistance for private companies on a contract basis. The cost for evaluation of soybean genotypes, as described above, utilizing two categories - resistant (< 10% of Lee 74) or not resistant (> 10% of Lee 74) - is $5.00 per individual cone-tainer. Categorizing genotypes as resistant (< 10% of Lee 74), moderately resistant (> 10% but < 30% of Lee 74), moderately susceptible (> 30% but < 60% of Lee 74), and susceptible (> 60% of Lee 74) is $10.00 per individual cone-tainer. The cost for obtaining actual counts of the number of SCN females formed on each plant root is $15.00 per cone-tainer. There may be a $150 charge for cone-tainers containing the HG Type and SCN race differential soybean genotypes; check with Greg Tylka or Chris Marett.. One half of the charge is due at the time the experiment is initiated and the balance of the fee is due after the results are received by the client. Checks should be made to Iowa State University and mailed to Dr. Gregory L. Tylka, Department of Plant Pathology, 351 Bessey Hall, Iowa State University, Ames, IA 50011.