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Degree

Master of Science, Ohio State University, Plant Pathology, 2009.

Abstract

Phytophthora sojae is one of the most destructive soybean pathogens. Thus far, fourteen race-specific resistance genes (Rps) towards P. sojae have been identified, however new pathotypes have emerged as they were deployed. In response to the emergence of many new pathotypes, novel Rps genes need to be identified. PI 408211B was proposed as a source of novel resistance genes for P. sojae. The objective of this study was to map one locus for resistance to isolate OH17 (vir.1b, 1d, 2, 3a, 3b, 3c, 4, 5, 6 and 7) and the three candidate genomic regions for resistance to isolate OH25 (vir.1a, 1b, 1c, 1k and 7). In three separate mapping populations, resistance to OH17 was mapped to Rps1 region on chromosome 3 where there is a R-gene cluster with simple sequence repeat (SSR) and single nucleotide polymorphisms (SNPs) markers. The resistance locus for OH17 was flanked by SSR markers GM3093 and GM3203, both with a genetic distance of 2.1cM from the locus, but the allelism test for this locus to Rps1 was unsuccessful. Bulk segregant analysis (BSA) was used to identify three loci for resistance to OH25 in a Stressland x PI 408211B BC₄F_2:7 population. Twelve DNA pools each with sixteen to twenty resistant individuals and a DNA pool of all susceptible individuals were screened with two hundred and nineteen SSR markers covering twenty chromosomes. The results of the BSA indicated that the resistance to OH25 in PI408211B was conferred by novel loci as SSR markers previously linked with known Rps locus were not associated with the resistance. In addition, ten homozygous resistant isolines were selected from this population and screened with eight hundred and eighty SNP markers to detect introgressions from PI 408211B potentially carrying novel resistance loci. Two putative loci were identified by BSA and single marker association analysis. One region tagged with Sat_044 and its adjacent markers on chromosome 9 (MLG K) associated with resistance to OH25 was identified in Stressland x PI 408211B BC₄F_2:7, Strong x PI 408211B BC₄F_2:3 and PI 408211B x Williams F_4:6. Another region tagged with Satt660 and Satt549 on chromosome 3 (MLG N) associated with resistance to OH25 was identified through single marker association analysis in PI 408211B x Williams F_4:5, and one introgression of PI 408211B was detected close to that region in Strong x PI 408211B BC₄F_2:3. Efforts were made to identify an isolate to which only one of these three loci conferred resistance, but no such isolate was identified to fine map one of the novel loci in PI 408211B.

Subject Headings

Plant pathology

Keywords

Phytophtora sojae; soybean; resistance; mapping

Committee / Advisors

Anne E. Dorrance, Ph.D. (Committee Chair)
Rouf Mian, Ph.D. (Committee Member)
Thomas K. Mitchell, Ph.D. (Committee Member)

Pages

128p.

Document number: osu1262123960
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=osu1262123960

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