Resistance Gene Pyramiding and Rotation to Combat Widespread Soybean Cyst Nematode Virulence

Area of Science:

• Plant Pathology and Nematology
• Agricultural Science
• Genetics and Breeding

Background:

• Soybean cyst nematode (SCN) causes significant annual yield losses exceeding $1 billion in the U.S.
• Current management relies heavily on SCN-resistant soybean cultivars, primarily using resistance genes from PI 88788 (rhg1-b) and PI 548402 (rhg1-a/Rhg4).
• Overreliance on PI 88788 rhg1-b has led to SCN populations adapting and overcoming this resistance, necessitating new management strategies.

Purpose of the Study:

• To evaluate the effectiveness of rotating soybean lines with different combinations of resistance genes against virulent SCN populations.
• To identify optimal resistance gene rotation strategies for managing SCN and preventing further adaptation to resistant cultivars.
• To provide guidance for sustainable SCN resistance management plans.

Main Methods:

• Eight SCN populations were developed through continuous selection on single resistance sources or rotations of soybean lines with pyramided resistance genes.
• Resistance sources included alleles from PI 88788 (rhg1-b), PI 437654 (rhg1-a/Rhg4), PI 468916 (cqSCN-006/007), and PI 567516C (Chr10).
• SCN population densities were monitored over eight generations, followed by HG type tests to assess population shifts and virulence.

Main Results:

• Continuous use of rhg1-b or cqSCN-006/007 showed limited effectiveness in reducing SCN type 1.2.5.7 population density.
• Rotation with rhg1-a/Rhg4 resistance significantly reduced SCN population density but selected for broader virulence (HG type 1.2.3.5.6.7).
• A rotation combining rhg1-a/Rhg4 with a pyramid of rhg1-b/cqSCN-006/007/Chr10 was most effective in reducing population density and minimizing selection pressure.

Conclusions:

• Strategic rotation of diverse SCN resistance genes is crucial for effective nematode management.
• The combination of PI 437654 (rhg1-a/Rhg4) with a multi-gene pyramid (rhg1-b/006/007/Chr10) offers a promising strategy to combat widespread SCN virulence.
• Implementing such rotation plans can help sustain the durability of SCN resistance genes and mitigate future SCN adaptation.