STUDIES ON CHARACTERIZATION AND BIOCONTROL POTENTIAL OF CHITINOLYTIC PLANT GROWTH PROMOTING RHIZOBACTERIA
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Date
2016
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ABSTRACT
Plant growth promoting rhizobacteria (PGPR) are root associated bacteria and benefit plants by
providing growth promotion through a variety of mechanism. The public concern over the harmful effects of
chemical pesticides on the environment and human health has enhanced the search for safer, environmentally
friendly control alternatives. Due to the importance of chitinolytic enzymes in insect, nematode, and fungal
growth and development, they are receiving attention in regard to their use as biopesticides and microbial
biocontrol agents. Therefore, the present study was aimed to characterize rhisospheric bacterial isolates
associated with various horticultural crops and medicinal plants. A total of eighty two bacterial isolates were
screened for chitinase production on minimal agar medium where zone of clearance and enzyme activity index
were used for initial screening of chitinolytic bacteria. Fifty two out of eighty two bacterial isolates were
selected as chitinase producers on the basis of zone size ranging from 1.60 mm to 45.40 mm and were further
screened for quantitative chitinase production. All the fifty two isolates were screened for multifarious plant
growth promoting traits viz. phosphate solubilisation, IAA production, siderophore production, HCN production
and antifungal activity against Fusarium oxysporum and Phytopathora capsici. Five bacterial isolates which
exhibited maximum chitinase activity along with maximum plant growth promoting traits were further evaluated
for their biocontrol potential against Fusarium wilt of tomato caused by FOL under net house conditions. One
isolates CT59T showed maximum biocontrol efficacy of 60.34 % against Fusarium wilt in tomato under net
house studies comparison to control where disease index of 91.67 % was recorded. On the whole maximum
disease control was found in case of fungal challenged tomato plant initially treated with CT59T. The
identification of CT59T was tentatively confirmed by biochemical characterization and it was identified as strain
belonging to Bacillus sp. The study on chitinase production by bacterial isolate was optimized under different
cultural conditions resulted in maximum chitinase production (52.80 U/ml) after 72 h of incubation at 40 °C in
minimal salt medium of pH 5.0 with an inoculum size of culture of 5.0 %. Bacterial isolate CT59T was grown at
optimum culture conditions and chitinase was partially purified by ammonium sulphate precipitaion at 20-70%
concentration and by dialysis of the proteins. The partially purified enzyme was characterized for stability of
enzyme activity and it was found to be stable within a pH range of 5-7, temperature range of 30-40 ºC and
reaction time of 90-120 minutes. The inhibition effect of crude and partially purified chitinase enzyme activity
from Bacillus sp. strain CT59T on Fusarium oxysporum f.sp. lycopersici showed its potential as biocontrol agent.