Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Baldwin, Brian S.

Committee Member

DuBien, Janice

Committee Member

Sciumbato, Gabe L.

Committee Member

Smith, James R.

Committee Member

Ray, Jeffery D.

Other Advisors or Committee Members

Klink, Vincent

Date of Degree

1-1-2013

Document Type

Dissertation - Open Access

Major

Agronomy

Degree Name

Doctor of Philosophy

College

College of Agriculture and Life Sciences

Department

Department of Plant and Soil Sciences

Abstract

Soybean is an economically important crop. It is a selfertilized species grown on vast contiguous acres. These facts predispose soybean to disease epidemics. Cercospora sojina, causal agent of frogeye leaf spot, has reduced United States soybean productivity 0.3 percent on average per year between 2008 and 2010. Several states have reported the pathogen developing resistance to the strobilurin class of fungicides. To date genetic host resistance has been identified as single dominant genes (Rcs1, Rcs2, and Rcs3). However, the lifespans of Rcs1 and Rcs2 were 10 and 16 years respectively. Currently, the Rcs3 locus has been utilized in all major soybean breeding programs of the US and has been for over 20 years. Seventyive accessions of soybean were found to exhibit resistance to multiple races of C. sojina while not exhibiting the Rcs3 haplotype. Twenty of these plant introductions (PIs) were screened by six races within the new race classification system of C. sojina representing all domestic variability of the pathogen. Two agronomically favorable PIs, PI398993 and PI399068, were found in this research to exhibit broad resistance to sources documented to contain most domestic variability of the pathogen. Two segregating populations were developed by crossing PI398993 x ‘Blackhawk’ and PI399068 x Blackhawk. Segregation ratios of F2 as well as F2:3 family seedling screens of both populations indicating single dominant gene action in both resistance sources. Single marker analysis indicated markers associated with the phenotype were indeed on chromosome 16 (MLG J), but possibly beyond Rcs3 in both sources. Interval mapping placed the highest probability of the resistance loci near SNP_171 and SNP_368, 72.86 and 72.48 cM respectively, but distal to the Rcs3 locus. Analysis of reaction ratings also indicated significant influence on phenotype was also associated with markers located at or beyond the published Rcs3 locus. The evidence in this research supports the hypothesis that both PIs may contain a resistance loci, potentially different than Davis, but within the same gene cluster. Equally as likely, the resistance could prove allelic to Davis.

URI

https://hdl.handle.net/11668/20513

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