Siderophore production by pseudomonas species and its role in disease control of green gram (Vigna radiata) caused by rhizoctonia solani
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Date
2006
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Publisher
CCSHAU
Abstract
In the present study, sixty-five bacterial isolates were
obtained from the rhizosphere soil of chickpea and green gram
plants by plating serial dilutions on King’s B media. Fifty-eight
isolates were identified as Pseudomonas based on colony
morphology, pigment characteristics and oxidase test. These
fifty-eight Pseudomonas isolates alongwith 22 reference strains
were tested for siderophore production using universal
chromo-azurol S assay method on MM9 medium and
iron-deficient succinate medium. Thirty-seven Pseudomonas
strains/isolates were found to produce siderophore on MM9
medium and the diameter of halo zone varied with different
Pseudomonas isolates. Production of siderophores was found
more on MM9 medium as compared to succinate medium.
Bacterial colony growth (G) and halo zone (H) size were measured
on MM9 medium and H/G ratios varied from 1.44 to 10.24 in
different Pseudomonas isolates.
Seventeen Pseudomonas isolates were used for
optimization of cultural conditions for enhanced production of
siderophores. Replacement of glucose with sucrose, sodium
gluconate or sodium malate supported siderophore production
whereas arabinose addition repressed siderophore production in
most of the Pseudomonas isolates. Increased concentration of
ammonium chloride (0.2%) also decreased siderophore
production. Addition of Fe-EDTA salt at low 5 M concentration
showed less suppressive effect whereas at 10 M concentration
more inhibitory effect on siderophore production was observed.
Production of siderophore was found more at pH 7.0 in
comparison to cultures grown in media with pH 8.0 and pH 6.0.
Siderophore producing Pseudomonas isolates inhibited the
growth of phytopathogenic fungi Fusarium oxysporum,
Rhizoctonia solani and Pythium aphanidermatum. Large inhibition
zones of fungal growth were observed on PDA medium in
comparison to NA medium plates.
Coinoculation of Pseudomonas cultures caused reduction
in root rot disease symptoms under pot house conditions and
disease control varied from 33.4 to 100 per cent with different
Pseudomonas cultures. Coinoculation of Pseudomonas isolates
MP20, MPS54, CP56 and CPS67 with Bradyrhizobium strain
SMR15 also enhanced the nodule number, nodule fresh weight
and plant dry weight as compared to Bradyrhizobium-inoculated
or uninoculated control plants at 30, 45 and 60 days of plant
growth. Coinoculation of Pseudomonas strain CP56 with
Bradyrhizobium strain and R. solani showed maximum increase
(275.8%) in plant dry weight at 60 days in comparison to control
plants and completely suppressed the root rot disease under pot
house conditions. The better performance of
siderophore-producing Pseudomonas strains in relation to
symbiotic performance and disease control indicated that
Pseudomonas strains could be exploited for disease suppression
and plant growth promotion under field conditions.