PGPR-Elicited Systemic Tolerance to Drought in Pearl Millet (Pennisetum glaucum L.)
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Date
2019
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DIVISION OF MICROBIOLOGY ICAR- INDIAN AGRICULTURAL RESEARCH INSTITUTE NEW DELHI
Abstract
Drought is one of the most common environmental stresses that affect growth and
development of plants and impact agricultural productivity in arid and semi-arid regions
of the world. Pearl millet is one of the major cereal and fodder crop in India and is
usually grown under rainfed conditions. It is usually grown as rainfed crop, however,
water stress considerably hinders its growth and yield. Thus, osmotolerant endophytic
bacteria possessing plant growth promoting activities can be harnessed for alleviation
of water deficit stress in plants.
Thirty one osmotolerant endophytic bacteria isolated from pearl millet, mustard
and cluster bean were used in the present investigation. These osmotolerant endophytic
bacterial isolates were evaluated for their potential in alleviation of water deficit stress
in pearl millet cultivar composite-443 under in vitro conditions. Only 6 endophytic
bacteria significantly improved shoot and root fresh weight and shoot and root dry
weight of plants under water deficit stress as compared to uninoculated control
conditions. Five isolates KPSR-2, MCL-1, MMS-3, MMS-5 and MKS-1 showing better
performance for most of the parameters studied were selected for evaluating their effect
on seed germination and seedling vigour under water deficit stress conditions.
Inoculation with two isolates MCL-1 and MKS-1 was observed to improve seedling
fresh weight and radicle length under osmotic stress condition. Based on their potential
for alleviation of water deficit stress, two promising osmotolerant endophytic bacterial
isolates MCL-1 and MKS-1 were selected for further studies.
Effect of different concentrations of PEG6000 on their growth was determined
by using spectrophometer and bioscreen techniques. It was observed that in presence
of 20% and 30% PEG 6000, there was less reduction in their growth. However, at higher
concentrations the isolates were able to grow but growth was drastically reduced. Effect
of different concentration of PEG 6000 on their PGPR activities under in vitro condition
and during plant endophyte-association were determined, under control, mild stress
(20%) and severe stress (30%)conditions. Under in vitro conditions PGPR activities
studied were P-solubilization, IAA production, GA production, exopolysaccharide
production, ARA and ACC deaminase activity. During plant-endophyte association
effect of the association under osmotic stress on production of IAA, GA and
exopolysaccharide was determined. The isolates were identified as Shewanella
putrefaciens strain MCL-1 and Cronobacter dublinensis strain MKS-1 by 16S rDNA
sequencing.
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A pot culture experiment was carried out under field capacity, mild water deficit
stress (-0.5 MPa) and severe water deficit stress (-1 MPa) conditions to evaluate the
effect of these cultures on pearl millet growth. Inoculation had a beneficial effect on
plant biomass, yield and root system architecture under field capacity, mild water
deficit stress and severe water deficit stress conditions. Photosynthetic parameters viz.
stomatal conductance, transpiration rate and chlorophyll content were significantly
enhanced in the inoculated plants under water deficit stress conditions. Various plant
physiological parameters viz. glycine betaine, proline, starch and phenolics were
significantly enhanced in the inoculated plants under water deficit stress conditions.
Phytohormone production viz. ABA, IAA and GA were significantly enhanced in the
inoculated plants under water deficit stress conditions. Inoculation with the
osmotolerant bacteria significantly improved membrane stability index and relative
water content in plants under water deficit stress conditions. Activity of antioxidative
enzymes viz. catalase and superoxide dismutase: and antioxidative status viz.
glutathione and ascorbic acid were significantly enhanced in the inoculated plants
exposed to water deficit stress conditions. Plant and grain nutrient status such as
nitrogen, phosphorus and potassium contents were considerably enhanced under water
deficit stress conditions due to inoculation with selected strains. Inoculation with these
osmotolerant strains significantly enhanced soil carbohydrate content, soil aggregate
stability and root adhering soil ratio under both mild water deficit stress and severe
water deficit stress conditions. The response of inoculation with Shewanella
putrefaciens strain MCL-1 was markedly more under both mild and severe water deficit
stress than that with Cronobacter dublinensis strain MKS-1. However, for most of the
parameters studied in present investigation, the inoculated plants gave better response
under severe water deficit stress as compared to mild water deficit stress and field
capacity conditions. Expression of drought responsive genes PgAP2, PgDREB2A,
CaP5CS, SbSNAC1, SbYUC, SbGA20OX and SbNCED was upregulated due to
inoculation with both the strains under severe water deficit stress condition as compared
to uninoculated control. Inoculation with both the strains upregulated PgAPX, PgLEA
and PgCSD gene expression under severe water deficit stress conditions as compared
to uninoculated control under similar stress condition.
As indicated in the present study, there was bacteria mediated elicitation of
systemic tolerance to severe water deficit stress in pearl millet. Thus, osmotolerant
endophytic bacteria possessing plant growth promoting activities can be used for
drought stress alleviation in crops and to improve plant growth under water deficit
stress.
Keywords: Drought stress tolerance, pearl millet, endophytes, osmotolerance
Description
T-10263
Keywords
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