Arbuscular mycorrhizas by contact with mycorrhized[i] Stylosanthes guianensi[/i]s enhance P use efficiency for N-2 fixation in the common bean ([i]Phaseolus vulgaris[/i] L.)

2Ecole Superieure d’Agriculture de Mateur, Bizerte, 7030, Tunisie. 3 Faculte des Sciences de Gafsa, 2112 Sidi Ahmed Zarroug, Tunisie. Accepted 17 January, 2012 Common bean (Phaseolus vulgaris L.) genotype Flamingo was inoculated with Rhizobium tropici CIAT899 and Glomus intraradices by mycorrhizal inoculant or by contact with mycorrhized Stylosanthes guianensis and grown under sufficient versus deficient phosphorus supply after transfer from initial sand culture, for comparing the effects of double inoculation (by contact or by inoculant) on growth, nodulation, mycorrhization of the roots, phosphorus use efficiency and total nitrogen. Although, the results showed that the double inoculation induced a significant increase in all parameters whatever the phosphorus supply and the cultivation systems in comparison to control and no significant difference between both arbuscular mycorrhizal fungi (AMF) treatments. Significant differences among colonization and nodulation of the roots and growth were found in both hydroaeroponic and sand culture. Nevertheless, the highest phosphorus use efficiency and plant total nitrogen were found under P deficiency in both AMF treatments. It is concluded that inoculation with rhizobial and arbuscular mycorrhizal fungi (by contact or by inoculant) could improve symbiotic nitrogen fixation even under phosphorus deficiency.