Co-evolution and Migration of Bean and Rhizobia in Europe

Abstract

Listen

Translate article

The legumes crop, as common bean, is one of the most important crops for the human nutrition, to be the protein basis from developing countries. This crop presents many limitations as are the deficiencies or toxicities of minerals in soils. These limitations in common bean production regions occur throughout the world. To overcome mineral deficiencies and toxicities, common bean growers must use corrective soil amendments. Symbiotic nitrogen fixation (SNF) is important as a source of N for agriculture, because the use of nitrogenous fertilizers has resulted in unacceptable levels of water and atmosphere pollution and by nitrate and N2O emissions, contributing to the increase of greenhouse effect. The common bean grown in Europe, and other continents, is the result of a process of domestication and evolution, from wild forms found exclusively in the Americas, and it is possible to distinguish two major domestication centers, Andean and Mesoamerican centers. Most of the European germplasm is from Andean locations since the type T phaseolin pattern is found in their seeds. It is thought that Mesoamerican lines were less popular because of their lower adaptability to winter cold and to short duration summers. Subsequently, new cultivars may have evolved within and between the two gene pools in Spain and Portugal making the Southern Europe a secondary center of diversity for the common bean. The microorganisms associated with the common bean plant for its SNF may exhibit a similar arrangement of genetic diversity in Mesoamerica and Andean gene pools. R. etli bv. phaseoli is the dominant microsymbiont in both the Mesoamerican and Andean centers of origin. Many other species have been found in bean nodules in region where they have been introduced. In Europe, rhizobia strains that nodulate common bean have a narrow genetic diversity that was correlative to beans being an introduced crop. In this respect, the large number of rhizobia species capable of nodulating bean supports the premise that bean is a promiscuous host and a diversity of bean–rhizobia interactions exists. Since there seems to be a large variation in the capacity of bean genotypes to nodulate with a large range of host or non-host-specific strains, this knowledge could be used to enhance the symbiosis and possibly to enhance nitrogen fixation.