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Functional Gene Analysis of Resistance QTL towards Phytophthora sojae on Soybean Chromosome 19

Stasko, Anna K
http://rave.ohiolink.edu/etdc/view?acc_num=osu1524139406566913

Abstract Details

2018, Doctor of Philosophy, Ohio State University, Plant Pathology.
Phytophthora sojae is the causal agent of Phytophthora root and stem rot of soybean. One of the most effective disease management strategies against this pathogen is the use of resistant cultivars, primarily through single gene, Rps-mediated resistance. However, numerous populations of P. sojae have adapted to most Rps genes that are deployed in modern soybean cultivars, rendering them susceptible to this pathogen. Quantitative resistance, conferred by quantitative disease resistance loci (QDRL), offers an alternative to Rps-based resistance. Previous studies mapped two QDRL to chromosome 19 in the soybean cultivar Conrad, which has a high level of quantitative resistance. A recombinant inbred line (RIL) population derived from a cross of Conrad by Sloan (a moderately susceptible cultivar) used for mapping these QDRL was advanced to the F9:11 generation. This population was used to map/re-map the QDRL towards three isolates of P. sojae, and one isolate each of Pythium irregulare and Fusarium graminearum, using the SoySNP6K BeadChip for high-density marker genotyping. A total of ten, two, and three QDRL and suggestive QDRL were found that confer resistance to P. sojae, Py. irregulare, and F. graminearum, respectively. Individual QDRL explained 2-13.6% of the phenotypic variance (PV). One QDRL for both Py. irregulare and F. graminearum co-localized on chromosome 19. This resistance was contributed by Sloan and was juxtaposed to a QDRL for P. sojae with resistance contributed from Conrad. Alleles for resistance to different pathogens contributed from different parents in the same region, the number of unique QDRL for each pathogen, and the lack of correlation of resistance suggest that different mechanisms are involved in resistance towards these three pathogens. Interestingly, the QDRL located on chromosome 19 contained several genes related to auxin processes, which are known to contribute to susceptibility to several pathogens in Arabidopsis and may contribute to susceptibility of soybean to P. sojae. In this study, auxin metabolites were measured in P. sojae mycelia, media from P. sojae liquid cultures, and inoculated soybean roots. Auxin precursors were detected in the mycelia of P. sojae as well as the synthetic media. More importantly, auxin levels were significantly higher in inoculated roots than the mock controls in both resistant and susceptible genotypes at 48 hours after inoculation (hai). To examine the role of auxin transport in susceptibility to P. sojae, the nucleotide sequences and expression of root-related soybean auxin efflux transporters, GmPINs, were compared between Conrad and Sloan. There were sequence differences between the two cultivars; however, experimental variability prevented accurate detection of expression differences through a quantitative PCR approach. An auxin transport inhibitor and a synthetic auxin were applied to Conrad and Sloan to assess changes in infection of these cultivars with chemically altered auxin processes. As with the gene expression analysis, experimental variation prevented us from determining the exact effect of these treatments. Finally, several different approaches were used to begin developing a system for functional gene analysis, including composite plant-based hairy roots, cotyledon-based hairy roots, and virus-induced gene silencing (VIGS). Composite plant-based hairy roots were difficult to inoculate with P. sojae, Py. irregulare, and F. graminearum. Cotyledon-based hairy roots allowed for more consistent inoculation with P. sojae and expedited experimental testing of RNAi constructs targeting candidate genes. One of these constructs was able to reduce the expression of its target gene in three soybean genetic backgrounds. A Bean pod mottle virus (BPMV) VIGS vector used here moved systemically into soybean roots but was not effective at silencing candidate gene targets in this tissue. Future studies should continue to refine environmental/experimental conditions to reduce variation and develop a reliable method of assessing change in quantitative disease resistance to define the roles of candidate genes.
Anne Dorrance, Ph.D. (Advisor)
Joshua Blakeslee, Ph.D. (Committee Member)
Leah McHale, Ph.D. (Committee Member)
Christopher Taylor, Ph.D. (Committee Member)
Feng Qu, Ph.D. (Committee Member)
352 p.
Plant Pathology
Phytophora sojae; soybean; quantitative resistance; auxin; high-density mapping; RNAi; VIGS;

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Citations

  • Stasko, A. K. (2018). Functional Gene Analysis of Resistance QTL towards Phytophthora sojae on Soybean Chromosome 19 [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524139406566913

    APA Style (7th edition)

  • Stasko, Anna. Functional Gene Analysis of Resistance QTL towards Phytophthora sojae on Soybean Chromosome 19 . 2018. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1524139406566913.

    MLA Style (8th edition)

  • Stasko, Anna. "Functional Gene Analysis of Resistance QTL towards Phytophthora sojae on Soybean Chromosome 19 ." Doctoral dissertation, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524139406566913

    Chicago Manual of Style (17th edition)

osu1524139406566913
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