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Research Highlights

Research Highlights
Rhg1, cqSCN Loci and Epigenetic Determinants of Resistance to Soybean Cyst Nematode

By Andrew Bent, University of Wisconsin-Madison 

Soybean cyst nematode (SCN) is the No. 1 yield-robbing pest facing the U.S. soybean industry. This project aims to improve the resistance of soybean to SCN. A major focus is to increase understanding of Rhg1, the most important SCN-resistance gene segment, in order to improve its effectiveness in commercially grown varieties of soybean. In addition, two genes from wild soybean that confer improved SCN resistance are being characterized and used to improve soybean resistance to SCN. 

Soybean breeders and growers are increasingly challenged by the fact that more SCN populations in growers’ fields are able to overcome resistance from PI 88788, the most common source of resistance to SCN. This is a topic of strategic importance to sustained profitable soybean production in the U.S. With FY19 USB funding of $213,706, much work has been done by the project team to advance discoveries and develop new germplasm resources. 

Figure 1. Map of the known distribution of the soybean cyst nematode, Heterodera glycines, in the United States and Canada from 1954 to 2017. Known infested counties are indicated in red. 

Several years ago, it was discovered that one reason some soybean plants are resistant to SCN is they have multiple copies of the Rhg1 locus. Both the number and the version of the Rhg1 locus affect resistance. Several varieties of soybean with different numbers of copies of Rhg1 have been developed, and it has been shown that more copies means more resistance in the soybean. This is a promising avenue for developing new SCN-resistant cultivars.  To enable this research, a rapid and inexpensive test to measure how many copies of the Rhg1 locus are present was developed. However, it was discovered that the copy number alone was insufficient. Information on how much the gene was expressed was also required to explain resistance, implying that resistance is also controlled by expression level. Methods of measuring expression have been developed, and work is now underway to manipulate levels of expression to increase resistance. 

The group also made a major discovery regarding mechanisms of Rhg1-mediated SCN resistance by discovering that a gene encoding an unusual variant of an “NSF” protein is required for the viability of soybean lines that carry resistance-conferring Rhg1 types.

In addition, finding new genes (not related to Rhg1) has been a goal of this project. An SCN-resistant Plant Introduction (PI) from the soybean germplasm collection was identified a number of years ago that is a wild relative of soybean (species Glycine soja). After a lot of crossing and mapping, the present project transitioned more to gene sequencing and cloning. Resistance was narrowed down to a small number of genes. The team is continuing to understand what these genes are and how they work and to incorporate them into lines for commercialization.

The group also generated soybean germplasm carrying novel combinations of Rhg1 genes that cannot be generated by conventional soybean breeding, but which may recover the effectiveness of Rhg1-mediated resistance against many SCN populations. 

This is a key program for USB in terms of SCN research. It focuses both on understanding the mechanism of SCN resistance, and also on practical development of germplasm with enhanced SCN resistance. In the long term, as growers experience more and more SCN overcoming PI88788, they will need more tools and resources to develop SCN-resistant seed and other solutions. This project will deliver the needed tools and resources.

To find research related to this Research Highlight, please visit the National Soybean Checkoff Research Database.