Date of Graduation

5-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Pengyin Chen

Committee Member

Kenneth L. Korth

Second Committee Member

Richard E. Mason

Third Committee Member

Vibha Srivastava

Fourth Committee Member

Ioannis E. Tzanetakis

Keywords

Biological sciences, Breeding, Gene pyramiding, Molecular marker, Resistance, Soybean, Soybean mosiac virus

Abstract

Soybean mosaic virus (SMV) causes the most serious viral disease in soybean worldwide. Seven SMV strains, G1 - G7, and three independent multi-allelic loci for SMV resistance, Rsv1, Rsv3, and Rsv4, have been identified. In the initial study, 299 soybean germplasm lines were genotyped for Rsv4 region, inoculated with SMV-G1 and G7 strains, and classified into several resistance groups. The Glyma.02g121400 locus was sequenced from ten soybean accessions, and alignment of the sequences revealed three SNPs displaying 100% polymorphic consistency when a soybean genotype carrying the Rsv4 gene was present. A cross between V94-5152 × Lee 68 was made to create linkage map revealing a distance of 3.6 cM between the Rsv4 and the closest SNP. Five Rsv4 candidate genes have been proposed in this region. In the second study, three SMV R-genes were pyramided by crossing J05 and V94-5152. The gene-pyramided line GP20, was crossed with Williams 82, F2 plants were genotyped and collated with phenotypic data of F2:3 lines inoculated with SMV-G1 and G7 strains. The results confirmed a successful incorporation of three genes into one soybean line. In the third study, soybean germplasm PI 438307 was crossed to Essex for the inheritance study, and to three differential parents for the allelism test. F2 population and F2:3 lines derived from all four cross combinations were screened with SMV-G7 strain. Additionally, F2 generation of PI 438307 x Essex were genotyped with two SSRs. The results revealed that resistance to SMV in PI 438307 is controlled by a single dominant gene at the Rsv4 locus. PI 438307 plants exhibited a unique symptoms; therefore, a new allele Rsv4-v was assigned to SMV resistance in PI 438307. In the final study, PI 96983 and York were crossed to evaluate allelomorphic relationship between Rsv1 and Rsv1-y. To break possible linkage, 3000 F2-plant population was phenotyped using the SMV-G1 strain. Occurrence of susceptible and segregating lines indicated tight linkage between two genes positioned in a distance of 2.2 cM. The Rsv2 symbol was proposed to be assigned instead of Rsv1-y. Results from this research may accelerate breeding efforts to develop multi-virus resistant crops.

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