Fine Mapping of the SCN Resistance Locus rhg1-b from PI 88788

Soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is the most economically damaging soybean [Glycine max (L.) Merr.] pest in the USA and genetic resistance is a key component for its control. Although SCN resistance is quantitative, the rhg1 locus on chromosome 18 (formerly known as Linkage Group G) confers a high level of resistance. The objective of this study was to fine-map the rhg1-b allele that is derived from plant introduction (PI) 88788. F₂ and F₃ plants and F_3:4 lines from crosses between SCN resistant and susceptible genotypes were tested with genetic markers to identify recombination events close to rhg1-b. Lines developed from these recombinant plants were then tested for resistance to the SCN isolate PA3, which originally had an HG type 0 phenotype, and with genetic markers. Analysis of lines carrying key recombination events positioned rhg1-b between the simple sequence repeat (SSR) markers BARCSOYSSR_18_0090 and BARCSOYSSR_18_0094. This places rhg1-b to a 67-kb region of the ‘Williams 82’ genome sequence. The receptor-like kinase gene that has been previously identified as a candidate for the ‘Peking’-derived SCN resistant rhg1 gene is adjacent to, but outside of, the rhg1-b interval defined in the present study.