Growth room bioassay evaluating the ability of soybean cyst nematode (SCN) inbred lines to parasitize six soybean germplasm lines, each containing a distinct type of SCN resistance.
Summary Content
The soybean cyst nematode (SCN, Heterodera glycines) is the most damaging pathogen of soybean and is widespread in Minnesota and most soybean-growing regions globally. SCN exhibits considerable variation in virulence (its ability to reproduce on different SCN-resistant soybean lines) as well as in morphology. This project focused on characterizing the phenotypic and genotypic diversity of SCN in Minnesota. A total of 182 inbred SCN lines were developed from field populations collected across soybean-producing areas of Minnesota. These lines were evaluated for virulence against six SCN-resistant soybean germplasm lines: Pickett (PI 548988), Peking (PI 548402), PI 88788, PI 90763, PI 438489B, and PI 567516C (Figure 1). The percentage of SCN lines to which each soybean line was resistant (defined as FI < 10) was: 46.7% for Pickett, 76.9% for Peking, 50.5% for PI 88788, 87.4% for PI 90763, 87.4% for PI 438489B, and 77.5% for PI 567516C.
Findings
Eight SCN races were identified among the inbred lines: race 1 (25.3%), race 2 (4.9%), race 3 (21.4%), race 4 (2.2%), race 5 (15.9%), race 6 (14.3%), race 9 (4.9%), and race 14 (11.0%). The relatively low number of SCN lines with FI < 10 on PI 88788 suggests that cultivars derived from PI 88788 may provide insufficient resistance in many Minnesota fields. Peking type of resistance is distinct to the resistance in PI 88788, and most SCN lines were avirulent to Peking-type resistance. Rotation of PI 88788-derived cultivars with Peking-derived cultivars remains a good strategy for managing SCN in Minnesota.
Whole-genome sequencing was conducted on 178 of the 182 SCN lines to assess genetic diversity (Figure 2). Single nucleotide polymorphisms (SNPs) were identified by comparing each SCN genome to the reference and to each other, resulting in a total of 528,952 SNPs used for analysis. Population genetic analyses revealed that a few inbred lines were genetically distinct from the rest. To confirm species identity, sequences for the 18S, 28S, and ITS genes were extracted and compared with sequence data for H. glycines, white soybean cyst nematode (H. sojae), sugar beet cyst nematode (H. schachtii), and cereal cyst nematode (H. avenae) from the National Center for Biotechnology Information (NCBI). All 178 lines were confirmed to be SCN.
Phenotypic and genotypic data were used to conduct a Genome-wide Association Study (GWAS) to identify genomic regions, or quantitative trait loci (QTLs), associated with SCN virulence. Sixteen QTLs were identified, with only one associated with virulence to more than one soybean line. Specifically, one QTL was associated with virulence to Pickett, two to Peking, two to PI 88788, four to PI 90763, three to PI 438489B, and three to PI 567516C (Figure 3). Except for one, all QTLs were specific to a single soybean line, suggesting that these loci may control virulence to particular resistance sources.
This study advances our understanding of SCN virulence diversity and genetics, providing valuable insights to help soybean breeders select effective resistance sources and evaluate SCN resistance in commercial breeding programs. The findings could support the development of molecular tests for SCN virulence, offering a cost-effective alternative to the traditional greenhouse bioassay used in HG type testing. Improved SCN management through the technologies developed in this study could lead to significant economic benefits for soybean growers by increasing yield and profitability.
