Document Type

Thesis - Open Access

Award Date

2017

Degree Name

Master of Science (MS)

Department

Agronomy, Horticulture, and Plant Science

First Advisor

Sunish K. Sehgal

Keywords

Triticum aestivum, BLS, Spot Blotch, GWAS, gene mapping, quantitative trait locus, recombinant inbred lines, SNP markers

Abstract

Spot blotch (SB), caused by Bipolaris sorokiniana (Sacc.) Shoem, and bacterial leaf streak (BLS), caused by Xanthomonas translucens pv. undulosa (Smith et al.), two important foliar diseases of wheat in the major production regions of the US and the world. Deployment of adequate host resistance against them depends on determining the resistance genes or quantitative trait loci (QTLs) responsible for the trait and identification of genetic markers linked to QTL that facilitate markers assisted breeding. We conducted two independent studies and characterized QTLs for BLS and SB resistance. In the first study, we constructed a genetic linkage map of 1,211 SNPs with 92 F5 recombinant inbred lines (RILs) developed from a cross between BLS resistant (SD52) and susceptible (SD1001) parental lines. Composite interval mapping (CIM) identified genomic regions (LOD≥2.3) on chromosomes 2B, 6D, 7A, and 7B linked to BLS resistance. The four QTLs for BLS resistance QBls.sdsu-2B-I (15.8%), QBls.sdsu-7A-I (6.1%) and QBls.sdsu-7B-I (10.9%), were derived from SD52 and aggregately explained 32.8% of the phenotypic variation. Also, a disease increasing QTL, QBls.sdsu-6D-I was identified from SD1001 accounting for 14.8% of the total variation. In the second study, we identified spot blotch resistance QTLs by evaluating 294 genotypes of hard winter wheat association mapping panel (HWWAMP) against Bipolaris sorokiniana (isolate SD40). Ranges of reactions were observed with ten highly resistant, 47 moderately resistant and 241 moderately susceptible to susceptible genotypes. Genome-wide association study (GWAS) using 15,590 highquality SNPs we identified six QTLs (p= <0.001) on chromosomes 2D, 3A, 4A, 4B, 5A, 7B that collectively explained 30% the total variation. SNPs highly associated (P-value <0.001) with spot blotch resistance were identified for all six QTLs (QSb.sdsu-7B-1, QSb.sdsu-5A-1, QSb.sdsu-4A, QSb.sdsu-2D-1, QSb.sdsu-3A and QSb.sdsu-4B). Comparative analysis with barley indicated the resistance locus on wheat chromosomes 2D, 3A, 5A and 7B in our study are syntenic to the previously identified locus in barley for spot blotch resistance on chromosomes 2H, 3H, 5H, and 7H. Genotypes resistant to spot blotch and BLS and highly associated SNP markers identified in our study could be useful germplasm for breeding for spot blotch and BLS resistance in wheat.

Description

Includes bibliographical references (pages 97-133)

Format

application/pdf

Number of Pages

176

Publisher

South Dakota State University

Rights

In Copyright - Non-Commercial Use Permitted
http://rightsstatements.org/vocab/InC-NC/1.0/

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