Abstract:

Soybean cyst nematode (Heterodera glycines Ichinohe) is one of the two most important nation-wide soybean diseases in China. Race 1 and 4 of the pathogen, especially the latter, are most popular in Huang-Huai Valleys and ZDD2315 and ZDD2226 have been identified as elite resistance sources. The present study was aimed to reveal the genetic mechanism of resistance to the two races by using the two resistant materials. Genetic analysis was performed under major gene + polygene mixed inheritance model in the four BC1F2 populations derived from the soybean crosses of Essex×ZDD2315, Peking×ZDD2315, PI88788×ZDD2226 and Peking×ZDD2226. The results showed that the resistance to Race 1 was controlled by two or three major genes, but no polygene effect detected. In Cross Essex×ZDD2315, three major genes contributed to the resistance to Race 1 with the heritability of 72.02%, while two dominant-epistasis major genes were detected with the heritability of 62.33% in Cross PI88788×ZDD2226. The two resistance sources, ZDD2315 and ZDD2226, might have the same resistant genes with Peking conferring resistance to Race 1 because the two crosses Peking×ZDD2315 and Peking×ZDD2226 did not segregate in reaction to Race 1. The resistance to Race 4 was mainly conditioned by three major genes plus polygene in the crosses of Essex×ZDD2315, Peking×ZDD2315 and PI88788×ZDD2226 with the major gene heritability of 67.76%, 72.46% and 53.25%, respectively and the polygene heritability of 24.48%, 21.31% and 35.77%, respectively. However only two major genes were identified in the cross of Peking×ZDD2226. All the F_1s and the detected additive effects had a similar response to susceptible parents, indicating the resistance to Race 1 and Race 4 mainly was controlled by recessive genes. Therefore, selection could be taken at early generations in breeding programs and pyramiding of genes resistant to both races should emphasize on resistance to Race 4 because most of the BC1F2 lines resistant to Race 4 also showed resistance to Race 1.

Key words: Soybean, Heterodera glycines Ichinohe, Inheritance, Major gene + polygene mixed inheritance model