Growth and virulence of Bacillus thuringiensis on cereals
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Date
2016
Authors
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Publisher
Punjab Agricultural University, Ludhiana
Abstract
Five Bacillus thuringiensis isolates including two procured isolates (B. thuringiensis
MTCC 868 and MTCC 4715) and three native isolates (Bt-4, Bt-10 and PAU Bt) were
evaluated on different cereal based medium, their effect of incubation time, pH and various
additives on the persistence of bacteria and its virulence against Spodoptera litura. Among
various cereals based liquid media, wheat recorded maximum spore count (28.07×108 CFU/
ml) and was significantly better than maize, rice and sorghum. The growth parameters viz
incubation time and pH were recorded and was found that maximum spore count (27.87×108
CFU/ ml) was recorded after 72 hours of incubation which was at par with 96 and 120 hours.
The maximum spore count (27.73×108 CFU/ ml) was recorded at pH 7.5 and was at par with
spore count (25.60×108 CFU/ ml) at pH 7.2. Influence of different additives viz
carboxymethyl cellulose, triton x 100, boric acid, methyl-p-hydroxybenzoate and glycerol on
the persistence of B. thuringiensis isolates was studied. It was found that the spore count
varied with the different concentrations of additives. The maximum spore count 26.33×108,
24.80×108, 23.93×108, 23.20×108 and 20.53×108 CFU/ ml were recorded at 0.1 per cent
concentration of triton x 100 and one per cent concentration of glycerol, methyl-phydroxybenzoate,
boric acid and carboxymethyl cellulose respectively. Laboratory bioassay
studies were conducted against the second instar larvae of S litura along with one commercial
formulation of B. thuringiensis var. kurstaki (DELFIN® WG) and untreated control. It was
found that among all Bacillus isolates maximum mortality (76.67%) was recorded in MTCC
868 at higher concentration (2.0%) after ten days of treatment. However, DELFIN® WG
formulation recorded maximum mortality of 99.98 per cent mortality against the second instar
larvae of S. litura after seven days of treatment at all concentrations.
Description
Keywords
Bacillus thuringiensis, Bioassay, Cereal based media, Spodoptera litura, spore counts