Soybeans are subject to a variety of diseases, insect and nematode pests that reduce yield potential and threaten production annually. The prevalence and impact of these pests vary by location due to environmental factors that influence the distribution of these pests and the stress they impose on the growing plant. Management practices, and the development of genetic resistance in soybean varieties, varies by region depending on the most prevalent disease pests and their potential impact. Soybean researchers in each region need to evaluate management practices and work with plant breeders to develop genetic resistance to the key pests in each region.

Objective 1) Incorporate the nematode resistance genes into the elite lines to develop SCN or multiple-nematode resistant and high-yielding soybean germplasm lines in MG 0 through VIII.
Develop productive soybean germplasm with resistance to regionally predominate SCN HG types using different sources of resistance across all maturity groups and/or with resistance to root-knot nematodes using both conventional and marker-assisted selection approaches

Objective 2) Identify novel sources of multiple nematode resistance from existing known resistant sources or by screening soybean germplasm from USDA Soybean Germplasm Collections.
Approximately 95% of all SCN resistant soybean cultivars used in U.S. soybean production are derived from two genetic sources, Peking and PI 88788. Continued use of the same resistance genes is causing selection pressure on SCN field populations, resulting in the nematode overcoming the resistance genes and a shift in SCN HG types found in farmers’ fields. The lack of diversity among known sources of SCN and RKN resistance in soybean makes it important to look for new resistance sources and new genes in soybean. We plan to identify novel sources of multiple nematode resistance from existing known resistant sources or by screening soybean germplasm from USDA Soybean Germplasm Collections with 400 lines in 2019 and a total of 1200 lines for next 3 years.

Objective 3) Map nematode resistance gene(s) to develop effective and breeder-friendly DNA markers for breeding selection.
Through previous support from USB, we have identified putative novel sources of nematode resistance. In this proposal, we intend to map these novel genes responsible for nematode resistance and to develop SNP markers for marker-assisted selection. We have already developed five plant populations for such genetic mapping efforts with the support from the previous USB project.

Updated December 10, 2019:
Soybean cyst (SCN) and root-knot (RKN) nematodes are the most yield-limiting pests of soybean in the USA. SCN is by far the number one yield-limiting pest and RKN is a major problem, particularly in the sandy or sandy loam soils in the southern USA. Although cultural practices in soybean production fields can help reduce some of the yield loss from nematode damage, these soil-borne pathogens have a wide range of hosts and can survive for many years in the soil. Currently, the development of nematode resistant soybean varieties is the most economical and effective means to control nematode damages in soybean production. Discovering novel sources of resistance and increasing available genetic diversity for SCN and RKN resistance are critical for long-term sustainability of host-plant resistance as a tool to combat SCN and RKN. This USB project is composed of six scientists (Drs. Aaron Lorenz, Univ. of Minnesota; Silvia Cianzio, Iowa State Univ; Andrew Scaboo, Univ. of Missouri; Pengyin Chen, Univ. of Missouri; Prakash Arelli, USDA-ARS; Zenglu Li, Univ. of Georgia) from five soybean producing states in the US that tackle the nematode problems, covering maturity from 0 through VIII. Our goals are to identify and utilize novel nematode resistance genetics from exotic soybean germplasm to develop multiple-nematode resistant germplasm lines and breeder-friendly DNA marker assays for marker-assisted selection to support commercial breeding efforts.

The project team had diligently and successfully developed a strong pipeline of soybean germplasm lines with resistance to SCN or RKN and competitive yield across all maturity groups (MG 0-VIII), which have been widely used in both private and public soybean breeding programs. In this project cycle, the team has developed or released 22 soybean germplasm/cultivars across maturity groups 0 to 8 and 22 MATs/transfers involving 19 soybean germplasm lines have been processed to transfer the enhanced germplasm to both private and public soybean breeders

The USB project on nematode resistance discovery and breeding has led to the discovery of putative novel sources of unique nematode resistant lines by Drs. Prakash Arelli and Zenglu Li using a novel genomic strategy. This is the first step to finding new genes to provide broad and more durable resistance in soybean. Based on these new sources, nine genetic populations with these putative novel sources of resistance have been developed with the collaboration efforts by the team. These populations are being used for mapping QTL/genes for SCN resistance and developing improved soybean germplasm with resistance to multiple nematode species.

In addition, the nematode resistance breeding team has published 12 articles in peer-reviewed journals and presented >15 posters or oral presentations at scientific meetings or talks in field days. This work will benefit the entire soybean value chain by providing new elite germplasm adapted to local growing conditions with resistance to SCN or multiple nematode species. It will also provide most desirable source materials to commercial and public breeders for utilizing in their crossing programs for development of high-yielding and nematode resistant germplasm and cultivars. DNA markers and QTL information generated from this project will also benefit all soybean researchers seeking a better understanding of the genetics and mechanisms underlying resistance.

• Growers will gain varieties with new, updated sources of SNC race resistance and gain yield upon more effectively controlling SCN in their field.
• Growers will gain varieties with RKN and RN resistance where these nematode species are predominant, and where few such varieties are currently available.

• At least 4 soybean germplasm lines possessing enhanced SCN and/or multiple nematode (SCN and RKN) resistance from MG 0 to VIII are released.
• At least 8 private and public soybean breeders/scientists’ begin to use germplasm developed in this project in their breeding programs, as evidenced by requests for material, MTAs and license agreements.
• As many as 5 novel germplasm lines with resistance to SCN are identified by greenhouse bioassays and marker genotyping analysis.
• 6 populations are developed using existing or novel germplasm sources for QTL mapping and evaluation.
• QTL discovered and genetic markers are developed for specific nematode resistance genes and are used by commercial breeding programs in their product development as evidenced by MTAs and license agreements.