Genetic characterization and fine mapping of the novel Phytophthora resistance gene in a Chinese soybean cultivar.

Phytophthora root rot (PRR), caused by Phytophthora sojae Kaufmann & Gerdemann, is one of the most destructive diseases of soybean [Glycine max (L.) Merr.]. Deployment of resistance genes is the most economical and effective way of controlling the disease. The soybean cultivar 'Yudou 29' is resistant to many P. sojae isolates in China. The genetic basis of the resistance in 'Yudou 29' was elucidated through an inheritance study and molecular mapping. In response to 25 P. sojae isolates, 'Yudou 29' displayed a new resistance reaction pattern distinct from those of differentials carrying known Rps genes. A population of 214 F2:3 families from a cross between 'Jikedou 2' (PRR susceptible) and 'Yudou 29' was used for Rps gene mapping. The segregation fit a ratio of 1:2:1 for resistance:segregation:susceptibility within this population, indicating that resistance in 'Yudou 29' is controlled by a single dominant gene. This gene was temporarily named RpsYD29 and mapped on soybean chromosome 03 (molecular linkage group N; MLG N) flanked by SSR markers SattWM82-50 and Satt1k4b at a genetic distance of 0.5 and 0.2 cM, respectively. Two nucleotide binding site-leucine rich repeat (NBS-LRR) type genes were detected in the 204.8 kb region between SattWM82-50 and Satt1k4b. These two genes showed high similarity to Rps1k in amino acid sequence and could be candidate genes for PRR resistance. Based on the phenotype reactions and the physical position on soybean chromosome 03, RpsYD29 might be a novel allele at, or a novel gene tightly linked to, the Rps1 locus.