Fine Mapping of Phytophthora sojae PNJ1 Resistance Locus Rps15 in Soybean (Glycine max (L.) Merr.)

Phytophthora root rot (PRR), which is caused by the oomycete pathogen Phytophthora sojae (P. sojae), is one of the most devastating diseases affecting global soybean production. The deployment of resistance (Rps) genes through molecular breeding is a sustainable strategy to control this disease. In this study, we finely mapped a novel resistance gene using two recombinant inbred line (RIL) populations: one comprising 248 F8:11 lines from a cross between the resistant cultivar ‘Guizao 1’ and the susceptible ‘B13’, and another consisting of 196 F7:8 lines from a cross between ‘Wayao’ (resistant) and ‘Huachun 2’ (susceptible). The gene in ‘Guizao 1’, designated as Rps15, was delimited to a 78 kb genomic interval on chromosome 3 (bin31), spanning the physical positions from 4,292,416 to 4,370,772 bp. This region contains eight predicted genes. Similarly, the resistance locus in ‘Wayao’ was mapped to a broader region on chromosome 3 (approximately 324 kb; 3,968,039–4,292,863 bp), which encompasses 16 genes. Expression analysis via quantitative real-time PCR of the candidate genes suggested that Glyma.03g036000 is likely involved in the resistance response to PRR. The fine mapping of this novel Rps locus provides a foundation for the future cloning of Rps15 and can be expected to accelerate the development of P. sojae-resistant soybean cultivars through marker-assisted selection.