An interdisciplinary research strategy to improve symbiotic nitrogen fixation and yield of common bean (Phaseolus vulgaris) in salinised areas of theMediterranean basin

The main findings of a cooperative research group of agronomists, plant bre eders, microbiologists, physiologists and molecularists to improve the symb iotic nitrogen fixation (SN-F) and N-2-dependent yield of common bean under moderate salinity in the Mediterranean basin are summarised. Agronomic sur veys in reference production areas show large spatial and temporal variatio ns in plant nodulation and growth, and in efficiency of utilisation of the rhizobial symbiosis. The latter was associated with a large rhizobial diver sity, including new bean nodulating species. Macrosymbiont diversity in SNF and adaptation to NaCl was found. However, contrasts between plant genotyp es could be altered by specific interactions with some native rhizobia. The refore, variations in soil rhizobial population, in addition to agronomic p ractices and environmental constraints, may have contributed to erratic res ults observed in field inoculations. At the mechanistic level, nodule C and N metabolisms, and abcissic acid content, were related to SNY potential an d tolerance to NaCl. Their relation with nodule conductance to O-2 diffusio n was addressed by in situ hybridisation of candidate carbonic anhydrase an d aquaporin genes in nodule cortex. The limits and prospects of the coopera tive strategy are discussed. (C) 2001 Published by Elsevier Science B.V.