Understanding interactions between osmotolerant rhizobacteria and mustard under water deficit stress conditions
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Date
2020
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DIVISION OF MICROBIOLOGY ICAR- INDIAN AGRICULTURAL RESEARCHINSTITUTE NEW DELHI
Abstract
Drought stress is considered to be one of the most predominant abiotic stresses, causing
a setback in crop production worldwide. Mustard is one among the major oil seed crops
of India that is grown in rainfed lands. Recent studies indicate that employing
osmotolerant rhizobacteria can help plants cope with drought stress which is an
ecofriendly and cost-effective method.
In the present investigation, eleven osmotolerant rhizobacterial cultures isolated
from mustard and nagphani plants were evaluated for their effect on growth and yield
of drought sensitive Brassica juncea variety Pusa Karishma LES-39 under water deficit
stress condition. Plants inoculated with Bacillus cereus strain NAD-7 and Bacillus
casamancensis strain MKS-6 exhibited superior performance in yield and growth, thus
were selected for further studies.
The effect of osmotic stress on mustard-rhizobacterial interactions was studied
in detail. It was observed that osmotic stress significantly affected the rhizobacteriamustard root interaction. Also the quality and quantity of sugar monomers of both the
rhizobacterial EPS was improved. The protein and phenolics profile of NAD-7 and
MKS-6 were altered in the presence of osmotic stress. It was also found that several
proteins of mustard roots were differentially expressed due to osmotic stress and
inoculation treatment. Further, a pot experiment was conducted to determine the effect
of inoculation with osmotolerant rhizobacterial strains NAD-7 and MKS-6 during
vegetative and reproductive growth stages under drought stress conditions. It was
observed that under drought stress, the inoculated plants exhibited better root and shoot
biomass over uninoculated treatment during both stages.
These observations led to investigation into the physiological, biochemical and
molecular mechanisms involved. The inoculated plants outperformed in various
parameters namely RWC, MSI and photosynthetic pigments in comparison to
uninoculated conditions. The net photosynthetic rate, stomatal conductance and sugar
contents were better in case of inoculated plants under drought stress. The proline
content was significantly reduced by inoculation under drought stress during both
stages and was interpreted as the improvement in plant health status by microbes. The
H2O2 content of inoculated plants was lowered significantly and the activity of SOD,
CAT and APX was significantly high in inoculated plants.
Finally the hormonal regulation of plant growth was studied under drought
during both stages. HPLC analysis of root samples showed that the level of auxin (IAA)
was significantly higher in inoculated plants under stress that must have influenced the
root growth during both stages. In leaves, the similar trend was followed for hormones
namely GA and ABA. This also was explanatory to improved shoot growth and
flowering. The expression of genes involved in the hormone biosynthetic pathways
BjYUCCA1, BjNCED3 and BjGA20ox correlated with the hormone levels. Similarly,
the transcript level of BjFeSOD and BjP5CSB, various stress signaling pathway genes
namely BjDREB1-2, BjDREB2 and BjNAC14 were upregulated in inoculated plants
under drought stress during both stages.
The data on biomass, yield and oil content upon inoculation showed relatively
superior performance even under drought stress conditions. It also appeared that the
vegetative stage was more responsive to rhizobacterial inoculation than reproductive
stage under drought. These investigations indicate the potency of rhizobacteria in
reducing the negative impacts of drought stress in mustard. It can serve as potent
biofertilizer to sustain crop production under stressed environment.
Keywords :- Bacillus cereus, Rhizobacterial, Biosynthetic
Description
T-10472