Fine Mapping of Co–x, an Atypical Disease Resistance Gene to Colletotrichum lindemuthianum in Common Bean

Anthracnose, caused by the phytopathogenic fungus Colletotrichum lindemuthianum, is one of the most important diseases of common bean, Phaseolus vulgaris. Various specific resistance (R) genes, named Co-, and conferring race-specific resistance to different strains of C. lindemuthianum have been identified. The Andean cultivar JaloEEP558 was reported to carry Co-x, conferring resistance to a highly virulent C. lindemuthianum strain. To fine map Co-x, 181 recombinant inbred lines (RILs) derived from the cross between JaloEEP558 and BAT93 (a co-x susceptible Mesoamerican breeding line) were genotyped with PCR-based markers developed using the genome sequence of the Andean genotype G19833. Analysis of RILs carrying key recombination events positioned Co-x at one end of chromosome 1 to a 58-kb region of the G19833 genome sequence. Annotation of this 58-kb region revealed eight predicted genes: four kinases, one zinc finger protein and three phosphoinositide-specific phospholipases C (PI-PLC), suggesting that Co-x is not a conventional R gene encoding a nucleotide binding-leucine rich repeat protein. Repeated sequences were also identified including one miniature inverted repeat transposable element (MITE). Comparative analysis between soybean and common bean reveals that Co-x syntenic region, is located at one end of Gm18, and carries Rhg1, a major QTL contributing to soybean cyst nematode resistance. In order to recover the target region in JaloEEP558 we are currently developing two complementary approaches: non gridded BAC library and long-range PCR followed by next generation sequencing.