- Common bacterial blight (CBB) of common bean (Phaseolus vulgaris L.), is one of the major diseases that decrease yield and quality. A major quantitative trait locus (QTL) for CBB resistance from line XAN 159 was transferred into two bean lines, HR45 and HR67. Previous studies identified that two markers are linked to this QTL but the chromosome location was not consistent. To identify more tightly linked markers and to verify the chromosome location, 65 additional markers were mapped using 81 recombinant inbred lines (RILs) derived from a cross HR67 x OAC95-4. The QTL was mapped to a 13 cM region on chromosome 1 and defined by eight molecular markers that explained 25-52% of the phenotypic variation. Six tightly linked amplified fragment length polymorphism markers (0.6-9.7 cM from the QTL peak) were converted into seven sequence tagged site markers, three of which were mapped to this QTL. Five tightly linked markers were used to screen 907 F2 plants derived from a cross HR45 x 'OAC Rex' and four of them were linked to each other within 4.2 cM. These markers may be useful in marker-assisted selection and map-based cloning of this major QTL. 2007 Her Majesty The Queen in Right of Canada.