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Title: Two independent QTL condition novel resistance to beet curly top virus in common bean landrace G122

Author
item Larsen, Richard
item KUROWSKI, C - Harris Moran Seed Company
item Miklas, Phillip - Phil

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2010
Publication Date: 9/14/2010
Citation: Larsen, R.C., Kurowski, C., Miklas, P.N. 2010. Two Independent QTL Condition Novel Resistance to Beet curly top virus in Common Bean Landrace G122. Phytopathology. 100:972-978.

Interpretive Summary: Beet curly top virus, often referred to as Curly top virus (CTV), is an important virus disease of common bean in the semiarid regions of the US, Canada and Mexico, and the only effective control is disease resistance. The landrace G122 is resistant to CTV but does not contain the Bct gene.that confers resistance to the virus. To determine if G122 contains unique resistance to CTV, two populations were derived from a cross between G122 and susceptible Taylor Horticultural, both in the cranberry market class, and evaluated for response to infection to natural CTV infection in three field experiments. A large group of DNA-based markers were screened in order to identify highly specific markers for use in placing the resistance loci on the linkage group maps of the common bean genome. We identified a major gene conditioning resistance to CTV which was located on linkage group 6 and in the vicinity of the bc-3 gene that confers resistance to Bean common mosaic virus and Bean common mosaic necrosis virus. Also discovered was another gene with minor effect that was located on linkage group 7 in the vicinity of Bct. When screened across 74 common bean cultivars and breeding lines, it was determined that one highly robust marker would be of useful for marker-assisted selection where the genes linked to resistance in G122 have been integrated into newly developed cultivars or advanced breeding lines.

Technical Abstract: Beet curly top virus, often referred to as Curly top virus (CTV), is an important virus of common bean in the semiarid regions of the US, Canada and Mexico, and the only effective control is disease resistance. The landrace G122 is resistant to CTV but does not contain the Bct resistance gene. To determine if G122 contains novel resistance to the virus, two populations, A and B, consisting of 98 F5:7 recombinant inbred lines (RILs) in total were derived from a cross between G122 and susceptible Taylor Horticultural and evaluated for phenotypic response to natural CTV infection in three field experiments during 2006, 2007 and 2008. RAPD and SRAP markers were screened via bulked-segregant analysis for cosegregation with disease incidence reaction across populations A and B. Genetic analysis revealed a major effect QTL that exhibited stable expression across three years in both populations. The phenotypic variation explained by the QTL in Population A (37.6%) was greater than in Population B (20.4%). The QTL integrated to linkage group 6 of the core map. A SCAR marker SQ14.974 was developed from a RAPD marker tightly linked with the QTL. The SQ14.974 SCAR, as determined by an assay of 74 common bean cultivars and breeding lines for the marker, exhibits potential utility for marker-assisted selection of the G122-derived QTL across a wide array of susceptible germplasm. A second minor effect QTL was detected. This QTL integrated to linkage group 7 of the core map and was located in the general vicinity of the Bct gene. Results clearly indicate G122 landrace possesses novel quantitative resistance, which represents the first report of QTL conditioning resistance to CTV.