DIFFERENTIAL SYMBIOTIC EFFICIENCY BY SHADING OF SOYBEAN NODULATED BY B-JAPONICUM AND B-ELKANII STRAINS

Symbiotic efficiency of soybean Glycine max L. cv. Doko nodulated by B R-33 (CB 1809) strain of Bradyrhizobium japonicum or BR-29 (29W) strai n of B. elkanii was investigated under two light intensities: full sun light or 30% of full sunlight. Plants were harvested during pod-fillin g and at maturity. Soybeans cultivated under full sunlight and inocula ted with strain BR-33 showed higher shoot dry mass and nitrogen accumu lation, nitrogenase activity, ureide-N in the xylem sap and grain yiel d than plants inoculated with strain BR-29, confirming the superior sy mbiotic effectiveness of strain BR-33. In contrast, soybean submitted to shading treatment showed no significant differences regardless of t he strain used as inoculant. When submitted to shading, plants inocula ted with BR-29 strain showed an increase in most of the variables obse rved while plants inoculated with strain BR-33 were not significantly affected by the level of shading. The results suggest that strain effi ciency used as an inoculant for soybean can be different in plants cul tivated either in the greenhouse or in the field. This can help to exp lain why the potential of hydrogenase activity to improve symbiotic ef fectiveness is still a matter of controversy when comparing results fr om different experiments. (C) 1997 Elsevier Science Ltd.