The purpose of the Regional Soybean Cyst Nematode (SCN) Test is to evaluate the best experimental SCN resistant soybean lines, maturity group I to IV, developed by public researchers in the U. S. and Canada. Policies for the Regional SCN Tests are the same as those used by the USDA Uniform Soybean Tests Northern Region.
Yield is measured after the seeds have been dried to a uniform moisture content and is recorded in bushels (60 pounds) per acre.
Maturity is the date when 95% of the pods have ripened. Delayed leaf drop and green stems are not considered in assigning maturity. Maturity is expressed as days earlier (-) or later (+) than the reference variety.
Height is the average length in inches from the ground to the tip of the main stem at maturity.
Seed quality is rated according to the following scores considering the amount and degree of wrinkling, defective seed coat (growth cracks), greenishness, and moldy or rotten seeds. Threshing or handling damage is not included, nor is mottling or other pigment.
1 = Very good 2 = Good 3 = Fair 4 = Poor 5 = Very poor
Seed Composition is measured on samples submitted to the USDA-ARS National Center for Agricultural Utilization Research, Peoria, Illinois. A 25-gram sample of clean seed is prepared by taking an equal volume or weight of seed from each replication. Protein and oil percentages are measured on these samples using infrared reflectance.
Lodging is rated at maturity according to the following scores:
1 = Almost all plants erect.
2 = All plants leaning slightly or a few plants down.
3 = All plants leaning moderately (45 degrees), or 25% to %0% of the plants down.
4 = All plants leaning considerably, or 50% to 80% of the plants down.
5 = Almost all plants down.
SCN/DISEASE SCREENING
Indiana’s greenhouse test: Soil from each field location is brought to the laboratory and used to test each SCN soybean line for resistance to the SCN population found in that field. Seeds of each soybean line are germinated in sand. When seedlings are several inches tall, sand is washed from the roots. Each seedling is placed in a 1-inch cell of a seedling tray partially filled with a soil: sand (1:3) mixture, 1 ml of inoculum is pipetted over the roots and additional soil/sand mixture is added to the cell. Three replicates of each entry are set up in this fashion. Inoculum is prepared by extracting cysts from field soil. Eggs and juveniles are released by dissolving the cuticle with sodium hypochlorite and mechanical crushing. Inoculum is adjusted to a concentration of 2000-3000 per ml. Plants are grown for a period of 8-10 weeks at a temperature around 75 F. When it is judged that development of second generation SCN females has taken place, roots are gently dipped in water to remove soil and sand. Entries are then rated as resistant (R), moderately resistant (MR), moderately susceptible (MS) or susceptible (S) based on the following scheme of a visual inspection of the roots. The entry is considered resistant if the total number of females on the root is judged to be less than 10, moderately resistant if number of females is 11-20, moderately susceptible if 21-50 and susceptible if higher than 50.
Illinois Sudden Death Syndrome rating: Plots were scored in the field by Southern Illinois University. All disease scores were interpolated to the R6.2 growth stage.
DI = SDS Disease Incidence (% of plants with visible symptoms).
DS = SDS Disease Severity (1 = mild chlorosis, 5 = severe leaf scorch, 9=premature plant death).
DX = SDS Disease Index (DI*DS/9)
Illinois SCN rating: SCN root score based on 0=0 cysts; 1=1-5 cysts; 2=6-10 cysts; 3=11-30 cysts; and 4=30+ cysts per plant (average of 5 plants per replication).