Common bean (Phaseolus vulgaris L.) is an important legume crop worldwide. However, abiotic and biotic stress limits bean yields to <600 kg ha⁻¹ in low-income countries. Current low yields result in food insecurity, while demands for increased yields to match the rate of population growth combined with the threat of climate change are significant. Novel and significant advances in genetic improvement using untapped genetic diversity available in crop wild relatives and closely related species must be further explored. A meeting was organized by the Global Crop Diversity Trust to consider strategies for common bean improvement. This review resulted from that meeting and considers our current understanding of the genetic resources available for common bean improvement and the progress that has been achieved thus far through introgression of genetic diversity from wild relatives of common bean, and from closely related species, including: P. acutifolius, P. coccineus, P. costaricensis and P. dumosus. Newly developed genomic tools and their potential applications are presented. A broad outline of research for use of these genetic resources for common bean improvement in a ten-year multi-disciplinary effort is presented.

Common bean ( Phaseolus vulgaris ) is the major food legume worldwide, making it an important target for novel approaches of genetic analysis. This study evaluated the use of ethyl methane sulfonate (EMS) for the generation of a mutant population for targeted induced local lesions in genomes (TILLING) in common bean. TILLING is a powerful reverse genetics approach that uses a large mutant population for identification of mutants in loci of interest. Based on overall survival, development, and yield of treated seed, 40 m m EMS was found to be an appropriate concentration for the generation of a mutant population in common bean genotype BAT 93. Higher concentrations of EMS resulted in survival rates of less than 10% and lower concentrations resulted in the generation of fewer mutants. Based on TILLING results from other species, a population of 5000 lines is estimated to be sufficient for saturation of the common bean genome. Phenotypic mutation frequencies and the isolation of targeted mutations in the BAT 93 mutant population indicate that mutagenesis was effective.

In common bean (Phaseolus vulgaris L.), Rhizoctonia solani Kühn is an important pathogen causing web blight (WB) in the tropics, and it is also a soilborne pathogen causing root rot (RR) worldwide. This pathogen is a species complex classified into 14 anastomosis groups (AG). AG 1-IA, AG 1-IB, AG 1-IE, AG 1-IF, AG 2-2, and AG 4 have been reported to cause WB of the aboveground structures of the plant, while AG 4 and AG 2-2 have been associated with RR. There is limited information, however, concerning the ability of particular isolates of specific AG to cause both diseases in common bean. Nine R. solani isolates, including three AG 1 and three AG 4 WB isolates and three AG 4 RR isolates collected from both leaves and roots, respectively, of common bean in Puerto Rico, were used to evaluate the response of 12 common bean genotypes to WB inoculated using a detached-leaf method and to RR inoculated using a solution suspension of R. solani mycelia in the greenhouse. All R. solani isolates were able to induce both RR and WB symptoms. RR readings were generally more severe than the WB readings. The RR isolate RR1 (AG 4) produced the most severe RR scores. A few bean lines had mean RR scores ≤4.4 for specific R. solani isolates on a scale of 1 to 9, with 1 representing resistant and 9 highly susceptible. However, all of the bean lines had mean RR scores ≥5.0 when inoculated with the isolates RR1, RR2, and RR3, which were determined to be AG 4 in this study. Significant line–isolate interactions were observed for the WB and RR inoculations for the three planting dates, suggesting a differential response of the common bean lines to the pathogen. This genotypic interaction may require bean breeders and pathologists to monitor the virulence patterns of R. solani in specific growing environments, while the compatibility of specific R. solani isolates to both aerial and root tissue needs to be considered for disease control strategies.