Effect of native mycorrhizal fungi inoculants on the growth and phosphorus uptake of tree legumes: Erythryna brucei and Millettia ferruginea

The inoculation study was conducted in the greenhouse to investigate the effect of phosphorus (P) concentrations on growth and arbuscular mycorrhizal fungi (AMF) colonization of multipurpose tree legumes Erythrina brucei and Millettia ferruginea. Plant growth parameters (shoot length, dry weight) and P uptake increased significantly after inoculations with AM fungi, Rhizophagus clarus, Rhizophagus intraradices and the mixed species. Results on effect of P application on total Mycorrhizal Dependency(MD) of studied tree species showed that maximum MD values were recorded for R. clarus (34.87%) in M. ferruginea and (26.19%) in E. brucei respectively. For the mixed species was recorded, the next highest MD values 26% in M. ferruginea and 16.67% in E. brucei. The least MD values were recorded for treatments with Rh. intraradices in both trees under study. The optimum P concentrations for maximum benefits from the AM symbiosis in aforementioned tree species varied from 0.005 to 0.02 mg g-1 and corresponding peaks of arbuscules, vesicles, percent root colonization, and spore count per 50 cm3 sand were noticed at similar concentrations. Thus, the results showed that the recorded plant growth peaks were due to AM colonization of the tree seedlings. Therefore, inoculating plants with a suitable AM inoculant could result in a benefit comparable to high P input and lead to a significant saving of inorganic P fertilizer.   Key words: Agroforestry, trees, root colonization, spore density.