Database Research SummariesEvaluation of the Phytophthora resistance Rps12 gene for its utility and identification of tightly linked molecular markers for its selection
Research Focus
The focus of this project is to determine if Rps12 truly confer broadspectrum Phytophthora resistance and identify perfect molecular markers to utilize this gene in breeding programs.
Objectives
- Determine the responses of three recombinant inbred lines carrying Rps12 to a large collection of P. sojae isolates.
- Identify molecular markers linked tightly to Rps12.
Results
- 30 simple sequence repeat (SSR) markers were generated and investigated these markers for polymorphisms between the resistant PI399036 and susceptible AR2 parents. Out of 30 SSR markers, 10 SSR markers were found to be polymorphic between the two parents and applied in evaluating the first set of 42 RILs homozygous for Rps12. From the polymerase chain termination reaction (PCR) assays of 420 combinations of 42 RILs and 10 SSR markers, we identified two RILs (RIL12 and RIL14) that carry the Rps gene-linked molecular marker alleles, mostly specific to the Phytophthora susceptible parent AR2.
- Of the 30 SSR markers evaluated, 10 SSR markers were found to be polymorphic between the two parents and were applied in evaluating 42 RILs homozygous for Rps12. From the polymerase chain termination reaction (PCR) assays of 420 combinations of 42 RILs and 10 SSR markers, we identified two RILs (RIL12 and RIL14) that carry the Rps gene-linked molecular marker alleles, mostly specific to the Phytophthora susceptible parent AR2. We have obtained 33 P. sojae isolates from the Robertson lab that were collected earlier from the Iowa soybean fields. The isolates were characterized for their pathotypes by inoculating a set of 14 soybean lines that are considered to be differential cultivars for 14 individual Rps genes. The isolates were used to infect the differential cultivars, as well as the two selected RILs (RIL12 and RIL14) and two parents, PI399036 and AR2, used to develop the RILs.
- RIL12 is susceptible to six P. sojae isolates collected from Iowa soybean fields. Based on the genetic make-ups of RIL12 and RIL14 for molecular markers of the Rps12 region and different responses of the two RILs to six isolates, it appeared that there could be a functional Rps gene (RpsX) linked to Rps12.
- Using the unassembled genome sequences of the two parents of the RILs, PI399036 and AR2, we identified single nucleotide polymorphic loci of the Rps12 region and converted to sequence-based polymorphic (SBP) markers.
- The new RpsX gene was mapped in a 72 kilobases DNA fragment located between Sat_064 and SSRG60684K markers. This distance is based on the Williams 82 genome. Exact size of the fragment in the PI399036 chromosome containing the RpsX gene could be different.
- Multiple functional Rps genes are evolved in tightly linked genomic regions to provide broad-spectrum Phytophthora resistance to a large collection of P. sojae isolates.
Importance
In the United States, the Phytophthora root and stem rot disease causes soybean yield suppression annually valued to over $300 million. Phytophthora resistant soybean cultivars will reduce this crop suppression and enhance profitability of soybean farmers.
For more information about this research project, please visit the National Soybean Checkoff Research Database.
Funded in part by the soybean checkoff.
