Abstract:
Biological nitrogen fixation was carried out by range of bacteria that are either free living, or in
symbiotic associations with plants (Rhizobium and Actinomycetes). The main objective of this
thesis was to isolate and characterize Rhizobia from Sesbania sesban and evaluation of its
symbiotic effectiveness. Root nodules were collected from young and healthy seedling of
Sesbania sesban. The nodule samples were collected from Sesbania sesban growing around
Ambo town. Five rhizobia isolates were obtained from the root nodule of Sesbania sesban and ch
aracterized morphological by standard procedure and different biochemical tests were
performed, the nitrogen nutrition effect on sesbania sesban of the five rhizobia isolated were
evaluated under greenhouse conditions and nitrogen content of the plants were analyzed by
standard method. All the quantitative data collected were analyzed by SPSS statistical software
for window version 25. Biochemical characterization of the rhizobia, physiologically as rod
shaped, gram negative, colony diameter which ranged from 2-4mm. and morphologically
characteristics as unable to hydrolysis the gelatin test, positive to peptone glucose test were
discovered. Rhizobium utilizes more glucose than others as carbon source. Most of them were
grown at 28C0
. All strain of rhizobium isolates were more grow in number on 0.5% salt concentr
ation. Whereas five isolates were more grown at PH 7.All isolates were sensitive to Chromophen
icol, tetracycline and doxycycline but all isolated was resistant against Cloxociline and ampicilli
n. Furthermore, most of the isolates showed a variation in nodulation with higher in AURAS5
(18+0.35 NN/p) and lowest in AUHCS1 (6+0.08NN/p) scores while, nitrogen fertilizer inoculated
sesbsania sesban not form nodule. Shoot dry weight (SDW) of the plant ranged from isolate MW
AS3 0.0887+0.03 to 0.2207+0.35 for isolate AURAS5 respectively. The isolates showed more
effective (70+0.03%) to highly effective (173+0.04%) N2- fixing performance of sesbania sesban.
The results of this study revealed that the possibility of supplementing or replacing chemical
nitrogen input in to agriculture by biological nitrogen fixation, but the more effective Rhizobia
isolates which able fix nitrogen in wide range of environmental stress need to be sought.
Generally sesbania sesban inoculated by rhizobium strain were high symbiotic effectiveness and
high nitrogen content when camper with –control N+& N-
.
