Abstract

This study was conducted through spring 2020 to prove the ability of various most common leguminous herbs; Medicago polymorpha, Medicago minima and Ononis viscosa, to observe symbiotic relationship via N2-fixation by rhizobial bacteria. Rhizobium meliloti associating with M. polymorpha forming fan shaped nodules and M. minima forming finger-like shape nodules, their nodules were distributed on adventitious roots. While Rhizobium trifolii was associated with O. viscosa in rounded nodules attached to the tap root. Larger nodule number was in O. viscosa with average (19.3) nodules/root, while the least number was in M. polymorpha with an average (4.43) nodules/root, with regard to the nodule length, the longest was for M. minima with (2.99 cm), and the least length was for M. polymorpha with average (1.59 cm). Bacteroid forms resulted here were varied between bacterial species inside nodule cells. To test the nodule activity, sections of M. polymorpha nodules were in black color, and sections of M. minima nodule were in light brown color, while O. viscose nodule sections appear in pink color. This study proved the existence of two types of nodules (determinate and indeterminate); indeterminate nodules in M. polymorpha and M. minima elongated with apical meristem and containing different central tissues. Other type was determinate nodule in O. viscose lacking the existence of active meristem leading to spherical nodules containing a single, homogeneous central N2-fixation zone.