Biological control of rice blast disease at seedling stage by bacterial antagonists
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Date
1994-03
Authors
Karki, Laxman Singh
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Abstract
Rice blast is a serious disease ~herever rice is grown.
Effective control through resistant varieties and chemicals
is avai I able but can be broken down because of the genetic
versatility of the pathogen. Alternative control methods such
as biological control would be a useful addition to existing
measures. As such this study was i nit ia ted to assess the
feasibility of biological control of rice blast in Malaysia.
Rice foliage samples were collected from different locations
in Kedah and Penang states. A total of 93 bacterial strains
were i. sola ted from the samples. The bacterial strains were
screened against the pathogen Pyr_icuJaria oryzae in vitro and
in vivo. Non-pseudomonad strains RLO 34 and RLO 31 were found
very effective in inhibiting the pathogen in agar plate
tests.
Preliminary in v_ivo tests. however, showed no correlation
between disease SURpressive ability and in vitro performance
of the isolates. In pot experiments, three strains RLP 17,
HLP 5 and RLO 12 w~re found to have potential in suppressing
disease severity. In a sihgle application, at the rate of 108
cfu/ml their individual disease score on a 1-9 scale was 4
with a pathogen concentration of lx105 spores/mi.
Strains HLP 17. HLP 5 and RLO 12 were also screened in microplots
under controlled conditions. The antagonists were
applied three times, first as a seed t rea tmen t and sprayed
twice. Disease control was more encouraging especially for
RLP 17. The mean disease score of RLP 17, RLP 5 and RLO 12
was 2. 7, 5. 7 and 6. 0 respect ivelJy as compared to B. 2 for
control plants.
Identification of the three strains was performed. The strain
RLP 17 was identified as Pseudomonas fluorescens, RLP 5 ·as P.
aureofaciens and RLO 12 as P. cepacia.
Studies to determine the mechanism of inhibition wet~e conducted
in vitro and in vivo. From these preliminary studies
iron regulated antibiotic p•·oduction was identified as the
possible mechanism responsible for the pathogen inhibition,
especially in the case of RLP 17 .
Description
Keywords
Rice blast disease , Bacterial antagonists