Plant Breeding Only Makes Sense in the Light of Evolution: the Role of Genetic Conservation in Cultivar Development.

Genetic diversity in germplasm collections and natural populations is unevenly distributed among species, populations or accessions and across genomes. There are multiple causes for this phenomenon, among which the reproductive biology, genome constitution, and phylogeny. In turn, a better understanding of the organization of genetic diversity in crop gene pools helps improve conservation of genetic diversity and the efficiency of breeding programs.

From an evolutionary perspective, the process of domestication, initiated some 10,000-12,000 years ago in most staple crops, is a key factor affecting the structure of genetic diversity in crop plants. Through processes such as mutation, genetic drift, gene flow, and selection, genetic diversity in the domesticated gene pool is markedly changed compared to the situation in the wild gene pool. Changed parameters include a reduction in levels of genetic diversity, an increase in linkage disequilibrium, the presence of selective sweeps reflecting selection at some stage during and after domestication, and evidence for gene flow between wild and domesticated types.

In this presentation, I will illustrate some of the effects of domestication and subsequent evolution on the genetic diversity of Phaseolus beans, principally P. vulgaris (common bean). This species was the first one for which geographically and culturally independent domestications were identified (in Mesoamerica and the southern Andes) from an already diverged ancestor. Additional findings include further subdivisions of the two major domesticated gene pools into eco-geographical races, parallel geographic distribution of genetic variation in some bean pathogens and Rhizobium, the simple inheritance of the domestication syndrome, and the differential susceptibility of different genome sections to the genetic effects of gene flow.

The consequences of these findings for the conservation of Phaseolus genetic resources and common-bean genetics, genomics, and breeding will be discussed, including broadening the breeding gene pool, the choice of parents in crosses, and the need of further recombination for additional breeding progress.