Abstract:
Phenotypic and genotypic diversity as well as symbio
tic effectiveness of twenty one
symbionts isolated from nodules of four Acacia species (
Acacia melanoxylon
,
A. mearnsii,
A. saligna
and
Acacia tortillis
) grown in Morocco were evaluated. Growth in various
media (YMA, YMA
-
BBT, YMA
-
RC), colony morphology, to
lerance to stress factors
(temperature, pH, salt concentrations, various heavy metals) and different carbon sources
were used as phenotypic markers. The genetic characterization was studied by
R
andom
A
mplification of
P
olymorphic DNA (RAPD) and
16S rRNA
gen
e sequencing. The
symbiotic effectiveness of rhizobial isolates on acacia was evaluated using plant
nodulation assay in controlled conditions. Results showed that twelve isolates were fast
growing, all of the twenty one
isolates
tolerated pH between 4.8 an
d 8.8 and temperatures
of 14, 22, 28
,
and 37°C, while only five could grow at 44°C and three at 55°C. Highest
resistance to heavy metals was recorded for arsenate, mercury, chromium; in contrast,
low resistance was noted for
c
opper (15 isolates resisted to
10
g
m
L
-
1
).
Most of the isolates
were able to grow
in a
wide range of carbohydrates. The genotypic analysis of
the
tested
isolates showed that they
could
be regrouped into three principal clusters based on their
RAPD profiles.
Acacia saligna
was principally
nodulated by
Bradyrhizobium
sp. while the
other species were nodulated by different rhizobial species.
Both phenotypic and
genotypic studies showed great rhizobial isolate
’
s
diversity. The symbiotic effectiveness
tests
showed that two isolates (AsF and As
A
g
1
)
had
high N
2
fixing potential on
Acacia
saligna
.
Keywords:
N
itrogen fixation,
Nodules, R
esistance to heavy metals
,
S
ymbionts
,
16S rRNA
.
