The domestication syndrome in Phaseolus crop plants: A review of two key domestication traits

Abstract

Plant domestication can be seen as a long-term experiment that involves a complex interplay among demographic processes and evolutionary forces. Longstanding questions about plant domestication are the number of times a species was domesticated, the extent of the domestication bottleneck, and the genetic basis of adaptive processes. Crops such as Phaseolus beans offer an excellent opportunity to answer these questions, especially the ones related to the genetic basis of the adaptive domestication syndrome. In the genus Phaseolus, five species have been domesticated: the common bean (P. vulgaris), the runner bean (P. coccineus), the tepary bean (P. acutifolius), the year bean (P. dumosus) and the Lima bean (P. Lunatus). These five species were domesticated in seven independent events that resulted in phenotypic convergence for several traits of the domestication syndrome. Two of these traits, namely reduced pod shattering and increased seed weight, are of special interest due to their role in the initial adaptation of these species during domestication. The objective of the present study was to review current evidence about (1) the effects of domestication on phenotypic variation of these two domestication traits in Phaseolus beans to understand whether adaptation led to clear-cut differences among wild and domestic forms or to a phenotypic continuum, and (2) the genetic basis of these two traits in Phaseolus beans to understand whether phenotypic convergence has been driven by parallel or convergent evolution. Research on these subjects in Phaseolus beans has been very scarce, and areas in need of urgent development are highlighted in this review.