Segregation for performance in recombinant inbred populations resulting from inter-gene pool crosses of common bean (Phaseolus vulgaris L.)

The germplasm of cultivated common bean exhibits a lower level of genetic diversity within each geographical gene pools (Mesoamerican and Andean) compared to that of the respective wild ancestors. Crosses between these two gene pools potentially provide a source of additional genetic diversity but their progenies have been characterized by phenotypic abnormalities and reduced productivity. In order to gain additional insights into this problem, we examined the segregation for performance in two recombinant inbred populations (RIPs) resulting from Mesoamerican x Andean crosses in three contrasting environments and two years. The two RIPs - 'California Dark Red Kidney' (of Andean origin) x 'Yolano' (Mesoamerican), n = 150, and A55 (Mesoamerican) x G122 (Andean), n = 67 - were grown in replicated field tests to assess the agronomic performance of each recombinant inbred line. Both populations exhibited, on average, greater days to maturity (DTM), lower biomass growth rate (above-ground dry weight/DTM), lower economic growth rate (seed yield/DTM), and lesser harvest index. In contrast with the conclusions of earlier experiments, there was no evidence from the field trials for a genetic association (due to linkage or pleiotropy) between seed weight and economic growth rate, but there may be a genetic association between seed weight and life cycle length. We compare the results of these studies with earlier experiments on inter-gene pool recombinant populations of common beans and relate our observations of diminished performance to models of speciation mechanisms.