Soybean Cyst Nematode (<em>Heterodera glycines </em> Ichinohe) Virulence Assay against Resistance Sources in Nebraska

Soybean cyst nematode (SCN, Heterodera glycines Ichinohe), one of the major yield-limiting pathogens of soybean, is currently found in 60 counties of Nebraska that produce more than 90% of the state’s soybean. Often, yield loss occurs without any above-ground symptoms, which makes it difficult to manage. The primary management option is the use of SCN-resistant varieties. Several soybean plant introductions serve as resistance sources against SCN. Unfortunately, the single source, PI 88788, is used in approximately 90% of resistant varieties and its prolonged use has increased the virulence status of SCN in the U.S. A study was conducted to assess the virulence status of Nebraska SCN populations on available resistant sources. 50 soil samples submitted by the Nebraska soybean producers in 2021, 2022, and 2023, through the Nebraska Soybean Board-supported SCN testing program, were randomly selected, tested for virulence, and assigned to HG Type. The results indicated the dominance of HG Type 2.5.7, followed by HG Type 1.2.5.7 suggesting increasing reproduction of SCN on the PI 88788, PI 209332, PI 548316, and Peking sources of resistance. To increase the lifespan of deployed resistance genes, it is necessary to rotate resistance sources while exploring alternate options to PI 88788. The second study assessed the genotypic diversity of SCN in Nebraska. Based on partial mitochondrial COI, two different haplotype groups were observed among 46 SCN populations, suggesting comparatively low SCN genetic diversity in the state. 44 samples clustered together to form a single dominant haplotype, while two samples constituted a less common haplotype group with four nucleotide substitutions. Continuous monitoring of SCN virulence phenotype and genotype diversity is important and has implications for the sustainable management of SCN in Nebraska soybean fields. Advisor: Dylan Mangel