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 d iversity within each geographical gene pools (Mesoamerican and Andean) comp ared to that of the respective wild ancestors. Crosses between these two ge ne pools potentially provide a source of additional genetic diversity but t heir progenies have been characterized by phenotypic abnormalities and redu ced productivity. In order to gain additional insights into this problem, w e examined the segregation for performance in two recombinant inbred popula tions (RIPs) resulting from Mesoamerican x Andean crosses in three contrast ing environments and two years. The two RIPs - 'California Dark Red Kidney' (of Andean origin) x 'Yolano' (Mesoamerican), n = 150, and A55 (Mesoameric an) x G122 (Andean), n = 67 - were grown in replicated field tests to asses s the agronomic performance of each recombinant inbred line. Both populatio ns exhibited, on average, greater days to maturity (DTM), lower biomass gro wth rate (above-ground dry weight/DTM), lower economic growth rate (seed yi eld/DTM), and lesser harvest index. In contrast with the conclusions of ear lier experiments, there was no evidence from the field trials for a genetic association (due to linkage or pleiotropy) between seed weight and economi c growth rate, but there may be a genetic association between seed weight a nd 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 m echanisms.