Objective 1. Compare performance of soybeans with resistance gene PI88788 to new resistance sources.
Based on survey work and 2020 field trials, a field with SCN pressure has been established at the Carvel Research and Education Center in Georgetown, DE. Four hybrids with differing resistance genes will be set up in a randomized complete block design with five replications. Ideally, treatments will include PI89772, Peeking, and PI88788 resistance sources. Plots will be approximately 25 ft in length and 10 ft wide. After seed is planted, soybean seedlings will be monitored for stand emergence, height, and disease symptoms throughout the duration of the trial. Currently PI89772 is only available in a 2.3 maturity group bean. While it is unrealistic for this maturity group to be planted in our region, the goal is to assess nematode reproduction and the viability of this resistance gene so we have an idea about performance as it becomes available in maturity groups more appropriate to our region. Due to differences in maturites, plots may be hand harvested at appropriate timing for each maturity group, dried for 24 hours, and all samples will be processed through a small plot combine following the final hand harvest.

Objective 2. Assess resistance gene effects on field populations of soybean cyst nematode.
Within each of the 20 treatment plots, a plot-representative soil sample will be collected by combining 30-40 soil cores per plot at three time points throughout the growing season. Plots will be assessed for nematode populations at the time of planting, approximately 30 days after planting, and at harvest. Samples will be submitted to the North Carolina Department of Agriculture Nematode assay service to be processed. Population counts will be provided for SCN, root knot nematode, lesion, lance, ring, spiral, and stubby root nematodes. Additionally, plants will be destructively sampled approximately 30 days after emergence to count live female cysts on the roots.

Objective 3. Share research findings through extension events and survey farmers regarding their concern towards soybean cyst nematode population increases and knowledge of resistance gene sources.
Findings from this project will be shared through the University of Delaware’s Weekly Crop Update which reaches over 700 growers, consultants, and stakeholders and provides a platform to discuss disease concerns and other production issues. Data will also be shared through training events and extension presentations such as Mid Atlantic Crop School, and the 2023 Delaware Ag Week. At University of Delaware hosted field days and commodity meetings, growers will be given a brief questionnaire to better understand concerns regarding nematode management and to investigate knowledge bases surrounding SCN resistance genes. In 2020, the United Soybean Board gave funding to the SCN Coalition to widen its reach to all states as data has shown that resistance gene PI88788, used in >90% of SCN-resistant soybean cultivars, is beginning to lose effectiveness. Dr. Koehler is a member of the SCN Coalition and questions used in this survey may include a set of questions released by the SCN Coalition to understand grower choices, perceptions, and
understanding of SCN host resistance.

Update:

View uploaded report

Soybean cyst nematode (SCN) (Heterodera glycines) is consistently ranked among the top destructive soybean pathogens across the United States and is the most significant nematode pest affecting soybeans in Delaware and the Eastern Shore of Maryland. SCN has been present in Delaware since 1979 prompting growers to rely on resistant varieties, primarily using the PI88788 resistance source. However, additional control strategies are needed as SCN populations have begun reproducing readily on these once resistant cultivars. A five-replication field trial was conducted in 2021 and 2022 to evaluate two additional resistance genes, Peking and PI89772, compared to lines with PI88788, for stand emergence, control of SCN, and yield differences. Soybean maturity group had the largest impact on yield, but the PI89772 resistance gene had the lowest numerical value of SCN at the end of the season in both years and numerically lower nematode reproductive factor than PI88788. If PI89772 is introduced to maturity groups appropriate for the region, this resistance source should be considered as an option to alternate with PI88788 in effort to reduce in-season nematode population increases.