The Great Lakes region of Central Africa is a major producer of common beans in Africa. The region is known for high population density and small average farm size. The common bean represents the most important legume crop of the region, grown on over a third of the cultivated land area, and the per capita consumption is among the highest in the world for the food crop. The objective of this study was to evaluate the genetic diversity in a collection of 365 genotypes from the Great Lakes region of Central Africa, including a large group of landraces from Rwanda as well as varieties from primary centers of diversity and from neighboring countries of Central Africa, such as the Democratic Republic of Congo and Uganda, using 30 fluorescently labeled microsatellite markers and automated allele detection. In addition, the landraces were evaluated for their seed iron and zinc concentration to determine if genetic diversity influenced nutritional quality. Principal coordinate and neighbor-joining analyses allowed the separation of the landraces into 132 Andean and 195 Mesoamerican (or Middle American) genotypes with 32 landraces and 6 varieties intermediate between the gene pools and representing inter-gene pool introgression in terms of seed characteristics and alleles. Genetic diversity and the number of alleles were high for the collection, reflecting the preference for a wide range of seed types in the region and no strong commercial class preference, although red, red mottled and brown seeded beans were common. Observed heterozygosity was also high and may be explained by the common practice of maintaining seed and plant mixtures, a coping strategy practiced by Central African farmers to reduce the effects of abiotic and biotic stresses. Finally, nutritional quality differed between the gene pools with respect to seed iron and zinc concentration, while genotypes from the intermediate group were notably high in both minerals. In conclusion, this study has shown that Central African varieties of common bean are a source of wide genetic diversity with variable nutritional quality that can be used in crop improvement programs for the region.

Drought stress is the major limitation of common bean (Phaseolus vulgaris L.) grown in subsistence farming systems worldwide. The objective of this study was to use single nucleotide polymorphism (SNP) markers from the BARCBean6K_3 Beadchip to identify quantitative trait loci (QTL) associated with traits related to drought tolerance in common bean. An intergene pool recombinant inbred line (RIL) population from a cross of drought tolerant line SEA5 and CAL96 cultivar was evaluated in Rwanda for 3 yr under drought stress and nonstress and in Colombia for 1 yr under drought stress. Traits evaluated included the numbers of days to flower, maturity, and seed fill; harvest index and pod harvest index; yield and yield components including number of pods per plant, seeds per pod, 100 seed weight (SW), and seed yield per day. Harvest indices, and SW were stable regardless of water treatment while number of pods per plant, seeds per pod, and yield were significantly reduced by drought. A linkage map of the RIL population spanning 1351 cM was constructed using 2122 SNP markers. The map covered all eleven bean chromosomes with an average distance of 0.64 cM between markers. A total of 14 QTL for performance under drought were consistently identified in different environments. Quantitative trait loci associated with phenology and SW traits mapped near previously reported QTL. Linkage between SW and yield QTL SY3.3SC was observed on Pv03 and could be used to simultaneously select for seed yield and size in intergene pool crosses of common bean.

Bean species and genotypes show wide phenotypic variability in relation to aluminium (Al) resistance and progressive soil drying. The objective of this study was to identify and characterize sources of resistance to Al toxicity and progressive soil drying among six genotypes of common bean (Phaseolus vulgaris), four of runner bean (P. coccineus), and one of tepary bean (P. acutifolius), using hydroponic and soil cylinder screening methods. One experiment on hydroponic screening of Al resistance was carried out using a basal nutrient solution with and without 20 lM Al. Two experiments were carried out using two oxisols in 80 cm long soil cylinders with high Al (HAl) and low Al (LAl) saturation treatments. The three experiments showed an average of 36.9-53.5% inhibition of root growth with HAl compared with LAl treatments. Differences in root development and distribution were observed among genotypes and species. Two accessions of P. coccineus (G35346-2Q, G35464-5Q) and one Andean common bean genotype (ICA Quimbaya) were outstanding in root and shoot growth in the HAl treatments. P. coccineus accession (G35346-3Q) was outstanding under combined stress of Al-toxic acid soil and progressive soil drying. Accessions of P. coccineus may represent unique sources of Al resistance for the improvement of common bean through interspecific crosses.