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ssss1 Genus Phaseolus includes five cultivated species that reside in four separate gene pools based on genetic distance. There is no restriction to intercrossing between members of the primary gene pool; crossing between primary and secondary gene pool requires that P. vulgaris is used as the pollen parent; crossing between primary and tertiary gene pool requires special techniques to rescue hybrid embryo; crossing is not possible between the primary and quaternary gene pools. In addition to the five cultivated species, there are over 50 wild Phaseolus species (Freytag and Debouck 2002).

Figure adapted from Gepts (2000).

Common bean originated from central Mexico (Bitocchi et al. 2012). From that region, wild P. vulgaris moved north and south and can be found today from northern Argentina to Chihuahua in northern Mexico (Ariani et al. 2018). There were more domestication events in the Mesoamerican than Andean gene region, which may explain the narrower genetic variation within the Andean gene pool observed in many genetic studies. The two gene pools of common beans have been clearly defined based on morphological, biochemical, and molecular characterization (Gepts 1988). One of the most noticeable differences is the larger seed sizes found in Andean gene pool in contrast to members of the Middle American gene pool. Interestingly, similar seed size differences are observed between the Andean (large‐seeded) and Middle American (smaller‐seeded) gene pools for lima bean. A further classification of gene pools of common bean into six races based on agronomic and adaptive characteristics was proposed by Singh et al. (1991). A fourth race, named Guatemala, was added as the climbing beans from Chiapas, Mexico, are unique from the three other MA races (Beebe et al. 2000). Beans also differ in plant growth habit, ranging from determinate types to climbing pole beans that require support.