Pyramiding of Alleles from Multiple Sources Increases the Resistance of Soybean to Highly Virulent Soybean Cyst Nematode Isolates

Soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is estimated to be the pathogen that causes the greatest economic loss to soybean [Glycine max (L.) Merr.] in the United States. Genetic resistance is an effective way to manage SCN. Resistance sources have been identified, and quantitative trait loci (QTLs) conferring resistance from these sources have been mapped. However, there is a need to diversify SCN resistance genes in cultivars, as most grown in the northern United States have resistance tracing only to the source PI 88788. The objective of this study was to determine the effectiveness of combinations of SCN resistance alleles from different sources in two populations formed via backcrossing. Population 1 segregates for a resistance QTL from both PI 567516C and PI 88788, whereas Population 2 segregates for the same QTL as Population 1 and two QTLs from PI 468916. Lines from both populations were evaluated with two virulent nematode isolates. Furthermore, a subset of lines from Population 2 (Population 2 Subset) was evaluated with two additional nematode isolates. The SCN resistance alleles from each source significantly increased SCN resistance compared with the alternative alleles. The effect of resistance alleles varied depending on SCN isolate and population, and there was generally an increase in resistance as more resistance alleles were stacked together. These results indicate that stacking multiple sources of resistance can be an effective means to increase broad-spectrum SCN resistance.