Analysis of Genes Underlying Soybean Quantitative Trait Loci Conferring Partial Resistance to <i>Phytophthora sojae</i>

Abstract

Few quantitative trait loci (QTL) have been mapped for the expression of partial resistance to Phytophthora sojae in soybean and very little is known about the molecular mechanisms that contribute to this trait. Therefore, the objectives of this study were to identify additional QTL conferring resistance to P. sojae and to identify candidate genes that may contribute to this form of defense. QTL on chromosomes 12, 13, 14, 17, and 19, each explaining 4 to 7% of the phenotypic variation, were identified using 186 RILs from a cross of the partially resistant cultivar ‘Conrad’ and susceptible cultivar ‘Sloan’ through composite interval mapping. Microarray analysis identified genes with significant differences in transcript abundances between Conrad and Sloan, both constitutively and following inoculation. Of these genes, 55 mapped to the five QTL regions. Ten genes encoded proteins with unknown functions, while the others encode proteins related to defense or physiological traits. Seventeen genes within the genomic region that encompass the QTL were selected and their transcript abundance was confirmed by quantitative reverse transcription polymerase chain reaction (qRT‐PCR). These results suggest a complex QTL‐mediated resistance network. This study will contribute to soybean resistance breeding by providing additional QTL for marker‐assisted selection as well as a list of candidate genes which may be manipulated to confer resistance.