Soybean cyst nematode: Challenges and opportunities

Soybean cyst nematode (SCN) is the primary pest responsible for yield losses of Glycine max. Management of SCN remains difficult in commercial soybean production due to the length of its biological cycle, frequent changes in population virulence, and ease of spread via infested soil. Effective management relies on crop rotation in combination with resistant cultivars, which have been derived from a limited germplasm base. Breeding for SCN resistance in soybean is difficult due to the quantitative nature of the trait, genetic variation within SCN populations, time required for phenotyping experimental soybean lines, and environmental factors affecting SCN reproduction. Quantitative trait loci associated with SCN resistance have been identified on 17 of the 20 soybean linkage groups, explaining 1-91% of the total phenotypic variation. Two major resistance genes, rhg I and Rhg 4, have been identified on linkage groups G and A2, respectively. Several minor resistance genes have been identified, but their importance varies with germplasm source and nematode race. Enhancement of SCN resistance in G. max may be achieved by interspecific hybridization with G. soja, the wild ancestor, or by engineering plants with candidate resistance genes such as Hs1(pro-1).