SELECTION OF RHIZOBACTERIA ANTAGONISTIC TO Ralstonia solanacearum E.F. Smith CAUSING BACTERIAL WILT IN TOMATO AND THEIR BIOCONTROL MECHANISMS
Loading...
Date
2001-08-08
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
UNIVERSITY OF AGRICULTURAL SCIENCES GKVK BANGALORE
Abstract
As many as 431 native rhizobacterial isolates of tomato were
screened in vitro on KB medium for the inhibition of Ralstonia
solanacearum causing bacterial wilt disease. Of them, 38 strains were
found to be potent antagonists with the zone of inhibition of the pathogen
varying from 8-20 mm dia., and 23 of them were fluorescent
pseudomonads. When assessed for mechanism of biocontrol, all the
potent antagonists produced at least one antibacterial metabolite:
antibiotics, siderophores, or HCN. Twenty five strains were found to be
antibiotic producers, 23 (only fluorescent pseudomonads) were
siderophore producers, 12 were HCN producers, 13 were both antibiotic
and siderophore producers, nine were both antibiotic and HCN producers,
12 were both siderophore and HCN producers and nine strains produced
all the three metabolites. In the green house experiment, Sid" and Sid''
mutants obtained by the Tn5 mutagenesis of fluorescent Pseuodumonas
strains RBL 101 and RSI 125, failed to control the disease as much as
their wild type did, thus confirming fluorescent siderophore production as
the mechanism of biocontrol in these strains. The green house
experiments revealed that 27 antagonistic strains were found to be plant
growth promoting (PGPR). The PGPR strains produced copious amounts of
plant growth promoting substances viz., lAA and GA. Thirteen
rhizobacterial strains were found to be deleterious (DRB), producing
unidentified gaseous metabolites. The unusual poor growth and biomass
of tomato in the UlC plants was due to the predominance of two
deleterious histosphere bacteria (DHB). However, the PGPR strain
fluorescent Pseuodumonas RDV 108 inhibited DHB and nullified its
inhibitory effect. The fluorescent Pseuodumonas strain RDV 107 was
found to be the best biocontrol agent with a per cent disease control of
77.30 besides exhibiting good root colonization ability, plant growth
promotion and siderophore and antibiotic production.
Description
Keywords
null