Evaluation location: Illinois, United States
Study Name: Response of soybean accessions from southern China to races 1, 3, 7, and 25 of Phytophthora sojae. Hypocotyl Inoculation Technique with Zoospores. Zoospore suspensions were injected into soybean plants. Each plant was injected three times at 1 cm intervals below the cotyledonary node in the center of the hypocotyl. Plants were not watered for at least 12 hours after inoculation to avoid washing off the inoculum. Plant Technique and Greenhouse Environment: Ten seed of each soybean line were planted 2.5 cm deep in 10 cm plastic pots filled with sand. Pots were watered to saturation each day prior to plant emergence and following emergence. Plants were grown and inoculated in the greenhouse under a 14-hour photoperiod with temperatures ranging between 210C and 290C. Seedlings were inoculated 8 to 14 days after planting, when the unifoliolate leaves had just opened. Plants with enlarged hypocotyls or late emerging plants were removed from the pot prior to inoculation. Plant Response Rating: Plants were rated for their response to P. sojae 4 to 5 days after inoculation. The number of living and dead plants in each pot was recorded. Pots containing greater than 70% alive plants or plants with non-killing lesions were rated as resistant; pots containing less than 30% alive plants or plants with non-killing lesions were rated as susceptible; pots containing less than 70% alive plants or plants with non-killing lesions but greater then 30% alive plants or plants with non-killing lesions were rated as heterogeneous. Resistant and susceptible checks were included in each test to evaluate the virulence of the pathogen.