Development and application of molecular markers in common bean breeding

Breeding efforts to improve yield and other quantitative traits, as well as resistance to common bacterial blight (CBB) caused by Xanthomonas campestris pv. phaseoli in common bean ( Phaseolus vulgaris L.) have proven to be difficult. The use of molecular markers will improve our understanding of the genetic factors conditioning these traits and is expected to assist in selection of superior genotypes.; The first study was conducted to examine the use of R7313 and R4865 RAPD markers for selecting CBB resistant material in a population derived from crosses between the resistant lines used previously in a linkage study and susceptible breeding lines. Seventy percent of the lines that had both R7313 and R4865 markers were classified as resistant, whereas 73% of the lines that had neither of the markers were susceptible. The results indicated that the markers and disease resistance remained associated in a plant breeding program and that they can be used for marker-assisted selection of CBB resistant beans.; The second study was conducted to identify a marker that is more closely linked to the CBB resistance locus than the R7313 marker. An AFLP marker (aca-ctg514) and a RAPD marker (M4868) were identified on either side of the gene at a distance of 5.6 ± 5.3 cM. The aca-ctg514 AFLP marker was converted into a sequence characterized amplified region (SCAR) marker for use in marker-assisted selection. The AFLP system had a higher marker utility score than the RAPD system. A low correlation was found between RAPD and AFLP-based genetic similarity matrices of interrelationships among the RI lines.; The third study was conducted to identify quantitative trait loci (QTL) affecting seed yield and its components, traits related to upright plant architecture, days to flowering and maturity, as well as resistance to CBB under field conditions in a population of 142 F_2:4 lines. The population was evaluated at two locations (Elora and Woodstock Research Stations, Ontario) in the Summer of 1998. Two experiments (Elora I and Elora II) were conducted at Elora Research Station. The Elora II site was inoculated with CBB. A map consisting of 114 markers was developed. This map shared 43 RFLP loci with a previous map in bean. Twenty nine QTL were identified for the 15 traits that were analyzed. The number of QTL identified per trait ranged from one to three. The multiple QTL model for each trait showed that these genomic regions accounted for 8.6% to 68.4% of the phenotypic variation of the traits. Ten of 26 (38%) QTL that were detected using mean data across environments were also detected in the three single environments.; A procedure to use the information from mapping and QTL studies for marker-assisted selection (MAS) was developed. Using mean genetic distances between the lines and the target parent based on UPGMA cluster analysis, and indices based on QTL-linked markers, the frequency of capturing high yielding lines was increased to 31% from 10% if selection was based phenotypic score in the whole population.