A Novel Phytophthora sojae Resistance Rps12 Gene Mapped to a Genomic Region That Contains Several Rps Genes

Abstract

<div><p><i>Phytophthora sojae</i> Kaufmann and Gerdemann, which causes <i>Phytophthora</i> root rot, is a widespread pathogen that limits soybean production worldwide. Development of <i>Phytophthora</i> resistant cultivars carrying <i>Phytophthora</i> resistance <i>Rps</i> genes is a cost-effective approach in controlling this disease. For this mapping study of a novel <i>Rps</i> gene, 290 recombinant inbred lines (RILs) (F<sub>7</sub> families) were developed by crossing the <i>P</i>. <i>sojae</i> resistant cultivar PI399036 with the <i>P</i>. <i>sojae</i> susceptible AR2 line, and were phenotyped for responses to a mixture of three <i>P</i>. <i>sojae</i> isolates that overcome most of the known <i>Rps</i> genes. Of these 290 RILs, 130 were homozygous resistant, 12 heterzygous and segregating for <i>Phytophthora</i> resistance, and 148 were recessive homozygous and susceptible. From this population, 59 RILs homozygous for <i>Phytophthora sojae</i> resistance and 61 susceptible to a mixture of <i>P</i>. <i>sojae</i> isolates R17 and Val12-11 or P7074 that overcome resistance encoded by known <i>Rps</i> genes mapped to Chromosome 18 were selected for mapping novel <i>Rps</i> gene. A single gene accounted for the 1:1 segregation of resistance and susceptibility among the RILs. The gene encoding the <i>Phytophthora</i> resistance mapped to a 5.8 cM interval between the SSR markers BARCSOYSSR_18_1840 and Sat_064 located in the lower arm of Chromosome 18. The gene is mapped 2.2 cM proximal to the <i>NBSRps4/6</i>-like sequence that was reported to co-segregate with the <i>Phytophthora</i> resistance genes <i>Rps4</i> and <i>Rps6</i>. The gene is mapped to a highly recombinogenic, gene-rich genomic region carrying several nucleotide binding site-leucine rich repeat (NBS-LRR)-like genes. We named this novel gene as <i>Rps12</i>, which is expected to be an invaluable resource in breeding soybeans for <i>Phytophthora</i> resistance.</p></div>