Novel Sources of Partial Resistance against Phytophthora sojae in Soybean PI 399036

Abstract

With the rapid emergence of novel pathogen pathotypes, durable sources of resistance against Phytophthora sojae in soybean [Glycine max (L.) Merrill] are needed to manage Phytopthora stem and root rot (PRR). This study used an inoculum source composed of multiple isolates of the pathogen to characterize partial resistance (PR) to P. sojae in plant introduction (PI) 399036. Two recombinant inbred line (RIL) F5:7 populations developed by crossing PI 399036 (high PR), with two germplasm lines (low PR), AR2 (AX20925) and AR3 (AX20931), were screened. Corrected dry weights (CDW—root and shoot) and percentage root rot data were collected. Inclusive composite interval mapping identified one putative quantitative trait locus (QTL) on chromosome 2 by all disease assessment parameters in the AX20925 population that explained 6 to 14% of the total phenotypic variation and five putative minor QTL on 5 chromosomes (3, 6, 12, 15, and 19) that individually explained 5 to 9% of the phenotypic variation. In the AX20931 population, two QTL, mapped to chromosome 9 and 17, were commonly identified by CDW while the QTL identified on chromosome 9 accounted for 21 to 30% of the total phenotypic variation. Additional QTL identified by CDW on chromosomes 9, 13, 14, and 15 individually accounted for 5 to 8% of the phenotypic variation. PI 399036 contributed the favorable alleles for the majority of the identified QTL. This study demonstrates the usefulness of PI 399036 as a novel source for breeding for resistance to PRR and that an inoculum mixture of P. sojae isolates with varying pathotypes can be used to identify putative QTL for PR to P. sojae using the rice (Oryza sativa) method.

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

“…PI399036 has been suggested to carry multiple Rps genes including known and unknown Rps genes [59, 60, 71]. Our previous study of two independent segregating populations suggested that there is a major Phytophthora resistance gene in the Rps4 /6 region of this accession [60].…”

“…Charlson, G. Gebhart, N. Rivera, P. Lundeen, and R. Shoemaker, unpublished). The cross was made at the Iowa State University research site at the University of Puerto Rico’s Isabela Substation (ISU-PR) [60]. …”

“…One hundred seeds of each individual F 6 plant were planted and harvested in bulk to obtain F 7 seeds [recombinant inbred line (RILs)] used in this study [60]. In this study, 290 F 7 families [recombinant inbred lines (RILs)] were phenotyped for responses to a mixture of three P .…”

“…In this study, 290 F 7 families [recombinant inbred lines (RILs)] were phenotyped for responses to a mixture of three P . sojae isolates [60] that overcome most of the known Rps genes. Of these 290 RILs, 130 were homozygous resistant, 12 heterzygous for Phytophthora resistance and 148 were recessive homozygous and susceptible.…”

“…Our recent mapping study of quantitative trait loci underlying partial resistance to P . sojae [60] using a mixture of three P . sojae isolates suggested the presence of a putative novel Rps gene on the lower arm of Chromosome 18.…”