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SYMBIOTIC
NITROGEN FIXATION IN ALFALFA (MEDICAGO SATIVA L.) BY
SINORHIZOBIUM MELILOTI AT AL-QASSIM REGIONS, SAUDI ARABIA
F.N. AL-BARAKAH1*
AND M.A.U. MRIDHA2
Abstract:
The nodulation status in alfalfa (Medicago sativa L.) plants by
Sinorhizobium meliloti under Saudi field condition was assessed
in some selected farms in four seasons for two years. In the present
study, we also monitored the introduced S. meliloti strains'
activity under Saudi soil conditions. The samples were collected at
regular seasonal intervals from the selected farms. The total number of
nodules, morphology of the nodules and the effectiveness of N2-fixation
was assessed. In general, it was revealed that soils in the selected
areas in Saudi Arabia have sufficient bacteria of the proper types to
nodulate the alfalfa plants. These nodules are high in number, small in
size and white in color. The nodules obtained from most of the selected
farms are ineffective for nitrogen fixation. Inoculation of alfalfa
seeds with imported S. meliloti strains failed to fix the
atmospheric nitrogen sufficiently and also the growth improvement of
alfalfa plants. There was a wide variation in the occurrence of number
of nodules among the four seasons in two years. It was also observed
that summer season severely affected the nodulation making it nearly
zero. This low number of nodules exerts a very slow recovery of nodule
formation in the next year. The introduced strains were always over
competing with the native strains but they did not survive
because of hot and dry summer. Nitrogenase activity of the nodules
collected from both the inoculated and non-inoculated farms were always
very low in all the collected samples, which indicates that the ability
of fixing nitrogen by S. meliloti strains in alfalfa under
Saudi soils conditions is very low.
Key words:
Alfalfa, Sinorhizobium meliloti, Nodule numbers and morphology, N2-ase
activity, Seasonal variation.
1Department
of Soil Science, College of Food and Agriculture Sciences, King Saud
University, Riyadh, Saudi Arabia
2Department
of Plant Production, College of Food and Agriculture Sciences, King Saud
University,
Riyadh, Saudi Arabia
*Corresponding
author's email: barakah@ksu.edu.sa
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