Pathogenic variation for the halo blight bacterium and mapping of loci for multiple diseases in common bean

Diseases of beans are primary constraints affecting bean production. Information on tagging and mapping of genes for disease resistance will be useful in designing selection programs in breeding. The objective of this study was to develop a random amplified polymorphic DNA (RAPD) marker linkage map using 78 lines of F9 recombinant inbred (RI) population derived from a bean cross Belneb-RR-1 x A 55. The genetics of a number of important bean diseases was studied and associated resistant factors in the genome were identified and their locations were estimated. The linkage map spanned 1272 cM including 176 markers consisting of 170 RAPDs, 1 SCAR, and 5 phenotypic markers. Markers were grouped into 13 linkage groups, 5 unlinked pairs, and 6 unassigned markers. The 78 RI lines were evaluated for resistance to a rust (Uromyces appendiculatus) pathotype, leaf and pod reactions of common bacterial blight (CBB) (Xanthomonas campestris pv. phaseoli) (Xcp), leaf and pod reactions of two halo blight (HB) (Pseudomonas syringae pv. phaseolicola) (Psp) strains, and bean common mosaic (BCM). Locations for a rust resistant locus (linked to marker BC227.1500), I gene controlling BCM resistance (linked to marker A10.1750), and flower and seed color genes, C and V, respectively, were identified. Two to four markers were found associated with QTLs for resistance to each disease accounting for 40% to 50% of the phenotypic variation of the trait. Some markers were found associated with QTLs for resistance to more than one pathogen or two strains of the same pathogen. The markers closely linked to the genes for resistance could be investigated for marker assisted selection. This RAPD map can be integrated with other linkage maps containing some common markers. Halo blight, caused by a bacterium Pseudomonas syringae pv. phaseolicola (Psp) is one of the most important bacterial diseases of snap beans and some dry bean types (Phaseolus vulgaris L.). Different races of Psp, based on reaction on bean differentials, have been reported. The objective of this study was to evaluate the pathogenic variation of Psp strains with emphasis on those collected in Nebraska. Twenty-nine Psp strains were inoculated on 20-day-old leaves of eight differential cultivars$\\$lines and a resistant check line great northern Nebraska #1 sel. 27. Two experiments were conducted in growth chambers under 20$\sp\circ$C and 12 hour photoperiod. A split-plot design was used with nine cultivars$\\$lines as a whole plots in a randomized complete block design (RCBD) and strains as subplots in an incomplete block arrangement. Data were analyzed as a split-plot with a RCB arrangement because incomplete block was not significant. Strains were classified into five races with six, sixteen and two strains were classified as races 1, 6, and 7, respectively. The remaining strains were designated tentatively as new races 10 and 11, respectively. Race 10 was different from race 1 because \u27Guatemala-196B\u27 was susceptible to race 10 and resistant to race 1. Race 11 differed from the existing nine races because of resistance to \u27Tendergreen\u27 and red mexican \u27UI 3\u27. Great northern Nebraska #1 sel. 27 was resistant to all Psp strains tested. This information is useful to breeders interested in developing germplasm and cultivars resistant to Psp