Unraveling agronomic and genetic aspects of runner bean (Phaseolus coccineus L.)

The (scarlet) runner bean (Phaseolus coccineus L.; 2n = 2x = 22) is an allogamous legume species from Mesoamerica that is cultivated as an annual crop for dry seeds and immature green pods in several parts of the world. It is grown especially in small-scale agriculture. From an agronomic perspective, it is predominantly indeterminate and climbing type of growth is associated with high labor and materials required to grow the crop with support structures. Intercropping (i.e., maize-runner bean) and seed inoculation using bio-compounds (i.e., rhizobacteria) have resulted in more efficient resource utilization, reduced risk to the environment and diminished production costs, which are valuable practices linked to sustainable agriculture. Cold tolerance and hive management due to allogamy are also distinctive features of runner bean production that have been studied. From a genomic standpoint, runner bean has been very little studied, despite the abundant development of molecular markers and genome sequencing of other legumes in the last decade, and more specifically common bean (P. vulgaris). The high genetic variability of runner bean is precious for breeding purposes, particularly as a source of disease resistance and cold tolerance. However, the lack of characterization of the P. coccineus germplasm restricts its utilization as donor species for inter-specific hybridization, and consequently limits its use in other Phaseolus breeding programs (i.e., common bean). Developing more broadly adapted, determinate cultivars that facilitate mechanical harvesting, assessing the potential presence of heterosis for hybrid seed production, and characterizing the germplasm of P. coccineus more extensively are great challenges and opportunities in the future that would increase its cultivation on a broader scale worldwide.