Plant growth promoting rhizobacteria , their characterization and mechanisms in the suppression of soil borne pathogens of coleus and ashwagandha
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Date
2008
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UAS Dharwad
Abstract
Major coleus and ashwagandha growing districts of Karnataka were surveyed for the
prevalence of wilt/root-knot complex in these crops. Survey revealed the association of
Fusarium chlamydosporum, Ralstonia solanacearum and Meloidogyne incognita with coleus
and ashwagandha. As many as fifty native plant growth promoting rhizobacterial (PGPR)
strains from healthy coleus and ashwagandha rhizospheres were isolated, maintained and
screened in vitro against F. chlamydosporum, R. solanacearum and M. incognita causing
wilt/root knot complex. Of them 19, 17 and 17 strains were respectively found to be highly
potent antagonists: Among these strains seven highly effective strains commonly inhibitory
to all the pathogens were selected and characterized as Pseudomonas spp. and used further.
When assessed for their mechanism of biocontrol, these potent antagonists produced at least
one antimicrobial antibiotic, siderophore, HCN, IAA, fluorescien, pyocyanin and volatile
metabolites. Molecular variability through RAPD-PCR showed highest (84 per cent)
similarity between rhizobacterial strains RB31 and RB50, though these were isolated from
geographically diverse locations.
A greenhouse experiment was conducted to assess the plant growth promotion and
vigour index by potent antagonists in coleus and ashwagandha. Talc-based bioformulations
were prepared for the promising strains and their efficacy was tested under pot and field
conditions. Bioformulations containing PGPR strains were evaluated against species of
Fusarium, Ralstonia and Meloidogyne (either individually or in combination) for their
efficacy to reduce the disease incidence and induced systemic resistance in coleus and
ashwagandha under glasshouse condition. Among the various bioformulations, strains RB50
and RB31 were found to be effective in increasing plant growth parameters, viz. plant height,
number of branches, fresh and dry weight of shoot and root, length of root, yield of coleus
and ashwagandha plants and also in decreasing number of galls (RKI) and disease incidence
in glasshouse and field conditions.