DIVERSITY OF OSMOTOLERANT ENDOPHYTIC BACTERIA IN PEARL MILLET
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Date
2014
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DIVISION OF MICROBIOLOGY INDIAN AGRICULTURAL RESEARCH INSTITUTE NEW DELHI
Abstract
Plant growth in agricultural soils is influenced by many abiotic and biotic factors. Water stress is a major
factor severely affecting crop productivity. Beneficial microorganisms colonizing plants’ interiors can
influence plant growth and development. Osmotic stress affects their survival, growth and plant growth
promoting activities. Osmotolerant plant growth promoting bacteria can be harnessed for their beneficial
properties in such environments in which other microorganisms hardly survive.
In the present investigation, endophytic bacteria were isolated from the drought resistant and susceptible
cultivars of pearl millet using various media selective for specific groups of bacteria. Bacteria belonging to
diverse groups such as gram negative bacteria, gram positive bacteria, oligotrophs, diazotrophs were found
harbouring interiors of pearl millet plant. Higher populations of gram positives and oligotrophs were obtained
in all the tissues and diazotrophic populations in leaves of both the cultivars of pearl millet. No fluorescent
pseudomonads were observed. A total of 215 morphologically different endophytic bacteria were isolated
from different tissues of the two cultivars such as roots, stem and leaves.
Out of 215 bacterial isolates screened, 50 isolates were found showing high osmotic stress tolerance.
Most of the isolates showed reduction in their growth under osmotic stress. Four isolates viz. KPRR22,
RPRS14, KPRL10 and MPSL2 showed higher growth in presence of osmotic stress as compared to control
conditions. Effect of osmotic stress on growth of the comparatively osmotolerant bacteria was determined. Out
of the 50 cultures screened, only 13 and 3 were able to grow in medium with 40% and 50% PEG 6000,
respectively.
These osmotolerant endophytic bacteria were characterized for their plant growth promoting activities
viz. P-solubilization, IAA production, nitrogen fixation, siderophore and HCN production and ACC deaminase
activity. These isolates were observed to possess multiple plant growth promoting activities. A very high
incidence of IAA production and siderophore production ability was observed. Nearly forty percent of the
isolates also possessed P-solubilization and ACC deaminase activity. Only three cultures possessed nitrogen
fixing ability. Osmotic stress had a beneficial effect on P-solubilization and HCN production abilities of most
of the isolates. However, osmotic stress had an inhibitory effect on IAA production, nitrogen fixation and
siderophore production abilities of most of the cultures.
All these isolates were analyzed for genetic diversity based on RFLP analysis of 16S rRNA. These
osmotolerant isolates were placed in 16 phylogenetic clusters, at 93% similarity, after RFLP analysis of their
16S rRNA. Sequencing of 16S rRNA of 16 representative isolates followed by BLAST search revealed that
the majority of the isolates belonged to Firmicutes and only a few belonged to Proteobacteria. Species of
Bacillus were the dominant osmotolerant endophytic bacteria colonizing interiors of pearl millet.
Description
t-9064
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