VARIABILITY PRESENT AMONG THE ISOLATES OF Pseudomonas spp. IN SAURASHTRA REGION OF GUJARAT 3748
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Date
2023-08
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JAU JUNAGADH
Abstract
Management of plant diseases is very important to attain a significant output in
a crop production system. There is a great threat to the environment and crop ecosystem
due to use of chemical pesticides even though they manage plant diseases effectively.
Furthermore, many chemicals are suspected to harm non-targeted organisms and
degradation of the environment especially soils.
Biological control of plant pathogens by microorganisms and improvement of
plant growth by enhancing nutrient uptake by roots is a potential non-chemical eco friendly tool. Members of the genus Pseudomonas have long been known for their
potential to reduce the plant disease caused by fungal pathogens and they have gained
considerable importance as potential antagonistic microorganisms.
A survey was carried out from seven districts of Saurashtra region viz.,
Bhavanagar, Jamnagar, Rajkot, Porbandar, Junagadh, Gir Somnath and Amreli to
collect soil samples from different fields of groundnut. Isolation and maintainance of
isolates of Pseudomonas spp. was done by applying dilution plate technique. The
colonies developed were yellowish with fluorescence under UV light.
To study cultural variability the bacteria were grown on different media viz.,
Aleksandrow agar, King's B, Potato dextrose agar, Pikovaskay's agar, Pseudomonas
agar, MacConkey Agar, and Nutrient agar medium. There was a difference in
characteristics of colonies viz., bacterial growth, appearance, pigmentation, colony
colour and fluorescence under UV light on seven different culture media.
All the isolates of Pseudomonas spp. were screened for siderophore production
by the CAS assay. Among thirty isolates tested, 27 isolates of Pseudomonas spp. were
positive for siderophore production. Isolates Pf1, Pf5 and Pf12 were negative for
siderophore production.
Biochemical tests of the Pseudomonas isolates were done by using KB002 Hi
Assorted Biochemical test kit (Himedia). The isolates Pf1, Pf10, Pf22 and Pf23 are
identified as P. aeruginosa and isolates Pf3, Pf5, Pf9, Pf17, Pf18 and Pf30 are identified
as P. putida and all the remaining isolates are characterized as P. fluorescens.
Among the isolates of Pseudomonas spp. tested for their efficacy against the
four soil borne fungal plant pathogens under in vitro condition, five isolates of Pf were
effective in variable degrees against Aspergillus niger, Sclerotium rolfsii,
Macrophomina phaseolina and Fusarium sp. Isolate Pf12 was most effective in
inhibiting A. niger, whereas isolate Pf30 was less effective. Isolate Pf26 was most
effective in inhibiting S. rolfsii, whereas, isolate Pf3 was less effective. Isolate Pf2 was
most effective in inhibiting M. phaseolina, whereas, isolate Pf17 was less effective.
Isolate Pf21 was most effective in inhibiting Fusarium sp. whereas, isolate Pf9 was less
effective. Isolate Pf24 was found common among five highly antagonistic isolates in
inhibiting mycelial growth of all four soil borne pathogens.
Highly antagonistic Pseudomonas isolate i.e., Pf24 was tested for compatibility
with fungicides, insecticides and weedicides at different concentrations. Among
fungicides tested, the isolate was highly compatible with carbendazim followed by
carbendazim 25% + mancozeb 50% WS. Whereas, hexaconazole was least compatible
with isolate Pf24. Among insecticides tested, the isolate was highly compatible with
fipronil followed by carbosulfan. Whereas, chlorpyriphos was least compatible with
isolate Pf24. Among insecticides tested, the isolate was highly compatible with
pendimethalin followed by quizalofop ethyl. Whereas, propaquizafop was least
compatible with isolate Pf24.
In pot culture studies the isolate Pf24 showed lowest disease incidence
percentage of 45% compared to control in case of collar rot of groundnut. The isolates
Pf2, Pf15 and Pf24 showed lowest disease incidence of 40% compared to control in
case of root rot of chickpea. The isolates Pf4, Pf21 and Pf24 showed lowest disease
incidence percentage of 50% compared to control in case of wilt of cumin