Variable Transfer of Soybean Genes for Resistance to Soybean Cyst Nematode

Abstract

Soybean [Glyclne max (L.) Merr.] cultivars may be resistant specific soybean cyst nematode (CN) (Heterodera glycines Ichinohe) populations due to genes for resistance from the genetically different sources of resistance ‘Peking’ and PI 88788. These sources have many genes for CN resistance, thus derived lines, particularly those with “mixed” or combination pedigrees, may not have all of the genes for resistance from either source. Experiments were conducted to determine whether soybean lines developed from the same sources of CN resistance had the same genes for resistance, as indicated by their phenotypes with different CN populations. Nematodes were selected for eight generations, to increase numbers of cysts, on single‐ source pedigree lines ‘Custer’ (source: Peking) and ‘Fayette’ (source: P188788), and on the two‐source lines ‘Pyramid’ and L82C‐ 579. Selection increased the nematodes' ability to reproduce on the selecting lines as expected. Patterns of ratios of numbers of cysts relative to ‘Essex’ indicated that four of the six two‐source lines were similar to Fayette. The exception, L82C‐579, appeared to have mainly Custer's genes for CN resistance. One line was heterogeneous; the phenotypes of individual plants tended to be like those of either Custer or Fayette. One of two one‐source (Fayette) lines was heterogeneous, based on evaluations with several selected nematode populations and inbreds. The results showed that soybean lines developed to be resistant to a specific CN race may not have the complement of genes for resistance that was present in the original sources.