Title of Thesis
Isolation and Biochemical characterization of efficient strains
of Rhizobium and Azospirillum from wheat and maize under water
Department Of Plant Sciences, Faculty Of
Biological Sciences / Quaid-I-Azam University, Islamabad
|Number of Pages|
|Keywords (Extracted from title, table of contents and
abstract of thesis)|
characterization, strains, Rhizobium, Azospirillum, wheat, maize, under, water, stress,
Water stress is one
of the most important environmental constraints that limit survival
and productivity of staple crops like wheat and maize particularly
in arid and semi-arid regions. Plant growth promoting Rhizobacteria
(Rhizobium and Azospirillum) are beneficial bacteria present in soil
and forming associations with roots of plants.
Present study was aimed at isolation and biochemical
characterization of Rhizobium and Azospirillum strains from roots
and rhizospheric soil of wheat and maize (at tillering and anthesis
stage) growing under different moisture regimes in the field and
under induced water stress in pots. The survival efficiency as
measured by log cfu/g, carbon/nitrogen utilization pattern
determined by QTS (Quick Test System), random amplification of
polymorphic DNA analyses, phytohormone production and 16sRNA
sequence analysis were done for isolated strains. The efficiency of
isolated strains to promote plant growth and development was tested
under induced water stress conditions in reinoculation studies.
The survival efficiency of Rhizobium and Azospirillum isolates from
plants of irrigated field (Experiment I) and those from well watered
pots (Experiment II) was higher as compared to that of Rhizobium and
Azospirillum isolates from roots and rhizosphere samples of arid (8
% soil moisture) and semiarid field ( 14 % soil moisture)plants and
waters stressed plants( 8 % soil moisture) in pots. There was no
significant difference in the survival efficiency between root and
rhizospheric soil isolates. The effect of low soil moisture on
colony forming unit was more pronounced at anthesis stage of plant
growth as compared to tillering stage. The value of cfu/g was higher
for isolates from maize as compared to that of wheat.
On the basis of carbon/nitrogen utilization patterns the Rhizobium
and Azospirillum isolates from wheat and maize field were placed in
three different groups depending upon the different moisture regimes
from where these strains were isolated.
The UPGMA (Unweighted Pair Group Method with Arithmetic Means)
cluster analysis based on Random Amplification of Polymorphic DNA (RAPD)
tests grouped Rhizobium and Azospirillum isolates in two. The
results revealed that QTS test can not solely be implicated to fully
characterize microbes and for better understanding of phylogenetic
relationship, molecular characterization e.g. RAPD-PCR is preferred.
The strains isolated from plants growing at semi arid regions in
field and under induced water stressed in pots at tillering stage
exhibited close genetic relatedness to the strains isolated from
plants growing under irrigated field conditions and well watered
conditions in pots respectively. While the strains isolated from
field plants growing at semi arid region at anthesis stage were
found to bear close genetic relatedness with the strains isolated
from plants growing in arid regions in field.
Reinoculation experiments with both field and pot isolates revealed
that the strains of Rhizobium and Azospirillum isolated from well
watered plants grown in field or pot have less effect on plant
growth of either chickpea or wheat used as host respectively,
whereas Rhizobium and Azospirillum isolated from arid fields and
plants growing under water stressed pot conditions performed better
exposed to induced water stress.
The amount of IAA, GA, ABA and trans zeatin riboside produced in the
presence of tryptophan was considerably higher as compared to medium
from which tryptophan was omitted. Moisture stress at all levels (14
to 8% soil moisture) decreased the production of IAA, GA and trans
zeatin riboside but ABA production was increased. These isolates
further showed bacteriocin production.
Degree of association of microbes appears to depend on developmental
stage and on its root architecture of host plants. Rhizobium and
Azospirillum isolated from arid field and induced water stress in
pots can be used as inocula to promote growth and yield of plants
grown in moisture deficit soil.