Short-term local adaptation of historical common bean (Phaseolus vulgaris L.) varieties and implications for in situ management of bean diversity

Recognizing both the stakes of traditional European common bean diversity and the role farmers' and gardeners' networks play in maintaining this diversity, the present study examines the role that local adaptation plays for the management of common bean diversity in situ. To the purpose, four historical bean varieties and one modern control were multiplied on two organic farms for three growing seasons. The fifteen resulting populations, the initial ones and two populations of each variety obtained after the three years of multiplication, were then grown in a common garden. Twenty-two SSR markers and 13 phenotypic traits were assessed. 68.2% of tested markers were polymorphic and a total of 66 different alleles were identified. FST analysis showed that the genetic composition of two varieties multiplied in different environments changed. At the phenotypic level differences were observed in flowering date and leaf length. Results indicate that three years of multiplication suffice for local adaptation to occur. The spacial dynamics of genetic and phenotypic bean diversity imply that the maintenance of diversity should be considered at the scale of the network, rather than individual farms and gardens. The micro-evolution of bean populations within networks of gardens and farms emerges as a research perspective.