Approximately 2.5 cm of washed pea gravel is added to Ray Leach Cones (20.6 cm long) to just above the drain holes. The cones are then filled with a sandy loam fumigated soil within 2 cm of the top. The cones are placed in the Ray Leach Trays (RL 98) in every other row (49 cones per tray).
Plastic ID stakes are placed in each cone and 3 soybean seeds of each tested genotype are planted in each cone and covered with a fumigated river sand. The first two cones in each test are known resistant and susceptible soybean cultivar checks. Extra rows of checks as well as a Race Determination Study is included in each test. Supplemental lighting is provided by 400-watt P.L. 90 Sodium Grow Lights. Seven to ten days after planting, seedlings are thinned to one per cone and inoculated with 2,000 cyst nematode eggs. The inoculum (2-4 ml depending on egg concentration) is dispensed with a digital pump, and placed next to the base of the seedling at a depth of 1 cm in the sand. The seedlings are lightly watered manually for 3 to 4 days after inoculation before placing the RL98 trays into the stainless steel trays. The stainless steel trays allow the seedlings to be watered uniformly from the bottom by filling the trays to cover the holes in the cones and soak for 2 hrs. prior to draining the water. Plants are fertilized weekly with a 20-20-20 (N=20%, P=8.7%, K=16.6%) fertilizer solution.
Thirty days after inoculation, roots from the check plants are examined for cyst nematode. If cyst nematode counts are high (15+) on the susceptible soybean check plants, the evaluation process begins. For evaluation, plant tops are excised and roots are gently washed free of soil. Root systems are examined under a lighted magnifying (20x) lens. When screening advanced breeding lines, a total cyst count per root system is obtained. For all other studies, the number of cyst nematodes on the resistant checks will determine the scale of R or S rating.
