Abstract
Osmotic constraints, nutrient deficiencies, especially phosphorus, and the lack of efficient strains of rhizobia in Mediterranean soils are major factors limiting symbiotic nitrogen fixation and yield in common bean (Phaseolus vulgaris). In order to improve yields, we investigated responses to rhizobial inoculation and P fertilization under glasshouse and field conditions with two bean cultivars, Coco blanc and BAT477. The nodulation test, using a hydroponic system in a glasshouse, revealed strong variability among 22 rhizobium strains of various origins, in their symbiotic efficiency, compared with Rhizobium tropici CIAT899. The introduced strains proved to be more efficient although some local rhizobia revealed high potential efficiencies. Glasshouse trials showed a significant effect of inoculation and P supply on nodulation, N content and shoot dry weight that varied with rhizobial strain. Field trials substantiated the glasshouse observations and emphasized the effects of cultivar-rhizobia interactions on symbiotic parameters and yields. It is concluded that inoculation with suitable rhizobia with supply of additional P is a technology that may improve symbiotic nitrogen fixation and yield in common bean in some soils under a Mediterranean climate.