Indole acetic acid production by Pseudomonas species and its effect on plant growth of green gram and black gram
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Date
2004
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CCSHAU
Abstract
In the present studies, IAA producing Pseudomonas strains CPS59 and MPS90 were
mutagenized with transposon Tn5 using E. coli strain S17-1. The frequency of mutants with low
amount of IAA production varied from 35.14 to 46.75% from Pseudomonas strains CPS59 and
MPS90, respectively and only 3.43 to 3.75% mutants produced higher levels of IAA in
comparison to respective parent strains in LB medium supplemented with tryptophan.
Inoculation of mutants derived from Pseudomonas strain CPS59 showed stunting effect on root
development of green gram seedlings at both 5 and 10 days of observation whereas mutants
CPS59-138, CPS59-162 and CPS59-231 showed stimulatory effect on root growth at 5 days in
black gram. Majority of the mutants caused stimulation of shoot growth at both 5 and 10 days of
observation in comparison to uninoculated treatment. MPS90-derived mutants i.e. MPS90-39,
MPS90-157, MPS90-102 and MPS90-106 showed slight stimulation of root growth whereas
most of the mutants showed stunting effect on shoot growth at 10 days in black gram.
Coinoculation studies of Pseudomonas mutants with Bradyrhizobium sp. strain S24
resulted in increased nodule number, nodule fresh weight and shoot dry weight in green gram
and black gram under chillum jar conditions. Shoot dry weight gains in green gram after
coinoculation with CPS59-derived mutants varied from 107-149 per cent and from 110-137 per
cent with MPS90-derived mutants in comparison to Bradyrhizobium-inoculated plants at 60 days
of growth. Similarly, shoot dry weight gains in black gram varied from 102-178 per cent and
105-198 after inoculation with mutants derived from CPS59 and MPS90, respectively. The
stimulation effect on shoot dry weight in comparison to uninoculated control treatment varied
from 280-390 per cent in green gram and 179-357 per cent in black gram. Four mutants CPS59-
138, CPS59-321, MPS90-133 and MPS90-51 showed more enhancements in nodule formation
by Bradyrhizobium strain S24 in green gram whereas mutants CPS59-162, CPS59-64, MPS90-
102 and MPS90-280 caused more stimulation for nodule formation in black gram at 60 days of
plant growth. Significant enhancements in shoot dry weights of green gram were observed by
coinoculation with Pseudomonas mutants CPS59-138, CPS59-231, CPS59-321, MPS90-280,
MPS90-14 and MPS90-145. Similarly, coinoculation of Bradyrhizobium strain with
Pseudomonas mutants CPS59-162, CPS59-321, CPS59-214, MPS90-102, MPS90-280 and
MPS90-51 showed significant gains in shoot biomass of black gram at 60 days of plant growth.
The better performance of IAA over producing mutants in relation to nodulation and plant
biomass indicated that IAA production by Pseudomonas strains is a beneficial trait for selection
of rhizobacterial strains having plant growth promotion ability.
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