Abstract
Pseudomonas syringae pv. phaseolicola (Psph) Race 6 is a globally prevalent and broadly virulent bacterial pathogen with devastating impact causing halo blight of common bean (Phaseolus vulgaris L.). Common bean lines PI 150414 and CAL 143 are known sources of resistance against this pathogen. We constructed high-resolution linkage maps for three recombinant inbred populations to map resistance to Psph Race 6 derived from the two common bean lines. This was complemented with a genome-wide association study (GWAS) of Race 6 resistance in an Andean Diversity Panel of common bean. Race 6 resistance from PI 150414 maps to a single major-effect quantitative trait locus (QTL; HB4.2) on chromosome Pv04 and confers broad-spectrum resistance to eight other races of the pathogen. Resistance segregating in a Rojo × CAL 143 population maps to five chromosome arms and includes HB4.2. GWAS detected one QTL (HB5.1) on chromosome Pv05 for resistance to Race 6 with significant influence on seed yield. The same HB5.1 QTL, found in both Canadian Wonder × PI 150414 and Rojo × CAL 143 populations, was effective against Race 6 but lacks broad resistance. This study provides evidence for marker-assisted breeding for more durable halo blight control in common bean by combining alleles of race-nonspecific resistance (HB4.2 from PI 150414) and race-specific resistance (HB5.1 from cv. Rojo).
Highlights
As an important contribution to the re-discovery of Mendelian genetics and its application in plant breeding, Biffen (1907, 1912) explained resistance to wheat yellow rust (Puccinia striiformis) by the inheritance of a single recessive gene and deployed the resistance allele in new Triticum varieties
Edmund combines resistances to halo blight (Pse-3 and quantitative resistance derived from PI 150414), Bean common mosaic virus (BCMV) and anthracnose (Colletotrichum lindemuthianum) (Conway et al, 1982)
In the SOA-BN × Edmund (SE) RIL population, halo blight resistance segregated in a bimodal distribution following separate inoculations with Race 6 and Race 1 in glasshouse experiments (Figures 2A,B, left graphs)
Summary
As an important contribution to the re-discovery of Mendelian genetics and its application in plant breeding, Biffen (1907, 1912) explained resistance to wheat yellow rust (Puccinia striiformis) by the inheritance of a single recessive gene and deployed the resistance allele in new Triticum varieties. Recessive or incompletely dominant disease resistance may indicate that a host protein, which is targeted by the pathogen in a compatible interaction, is either absent or has been mutated to a dysfunctional form (Fraser, 1986, 1990) This has been supported by molecular evidence of mutations in non-receptor proteins conferring recessive resistance to viral, bacterial and fungal pathogens (Collmer et al, 2000; Kang et al, 2005; IyerPascuzzi and McCouch, 2007; Orjuela et al, 2013; Wang et al, 2013). Phaseolicola (Psph) (Burkholder, 1926; Young et al, 1978), is a disease of major economic significance that can plague common bean (Phaseolus vulgaris L.) production worldwide This seed-transmitted disease favors cool and humid environments, occurring at higher latitudes in the northern and southern hemispheres and at higher altitudes in tropical and sub-tropical regions in Africa and South America. Alternative hosts present in the tropics, coupled with the commonly short periods between consecutive crops, are additional factors that limit the feasibility of maintaining pathogen-free seed of susceptible varieties (Taylor et al, 1996a)
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