This project had a single Deliverable: Findings that facilitate new soybean cyst nematode (SCN) control approaches. The project team was successful on all four Activities associated with this Deliverable. Progress on the four Activities is briefly summarized below.
Activity 1 sought to identify the specific soybean gene at the cqSCN-007 genetic locus that confers improved SCN resistance. This genetic locus is already the focus of elite soybean breeding efforts in the public and private sectors, but knowledge of the causal gene can facilitate better soybean improvement through more precise breeding, capacity to screen germplasm for better versions of the gene, and capacity to use gene editing or other approaches to improve this SCN resistance trait. The present project identified a candidate gene from among 11 previously identified candidates at the cqSCN-007 locus, focusing on this gene because induced reduction of this gene’s expression caused increased susceptibility to SCN in particular experiments. The research team also worked to improve cqSCN-007 functional testing parameters, to identify the best platform from which to most conclusively demonstrate and study the cqSCN-007 causal gene.
Activity 2 tested new GM Rhg1 gene combinations. Rhg1 is the soybean locus with the largest known impact on SCN resistance. Rhg1 is widely used in modern soybean varieties, but SCN populations are evolving and Rhg1 is gradually losing its effectiveness. Activity 2 seeks to generate and test novel improved combinations of Rhg1 genes that are not available in naturally occurring soybean germplasm. Elevated expression of Rhg1 a-SNAP proteins was engineered into lines that already carry Peking-type rhg1-a/Rhg4 SCN resistance. Incremental, statistically significant improvements in SCN resistance were observed. Importantly, no significant negative impacts on soybean seed yield were observed when this engineered trait was present. In further Activity 2 work, lines with elevated expression of two other resistance-causing genes from the complex Rhg1 locus were generated and initially screened. These lines will form the basis for future experiments to test if elevated expression of these genes can improve on native Rhg1-mediated SCN resistance.
Activity 3 generated soybean lines with new combinations of SCN resistance loci. The rhg1-a, rhg2, Rhg4, cqSCN-006 and cqSCN-007 genetic loci have all been identified as contributors to SCN resistance, but many combinations of these genes have not previously been generated and tested. Using DNA marker technologies, efficient breeding strategies were carried out that should produce, in the next project year, lines with various combinations of the above genetic loci, in soybean genetic backgrounds that exhibit elite yield performance.
Activity 4 is testing the impact of mid-season chemical treatments as a means of elevating soybean resistance to SCN. Approved, commercially available agricultural chemicals with known modes of action are being tested based on previous research results that suggested they could have beneficial impacts on soybean resistance to SCN. Initial results are sufficiently promising that the project is now being advanced and actively pursued in an expanded format.