Rhizobacterial strains as biocontrol agents against various soil pathogens
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Date
2008
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Publisher
CCSHAU
Abstract
A total of fifty three isolates/mutant were screened for their antagonistic
potential against three selected fungal soil pathogens; Rhizoctonia solani cotton, R.
solani rice and Fusarium oxysporum. Out of these 10, 6 and 12 isolates/mutant of
Azotobacter chroococcum were selected against R. solani cotton, R. solani rice and
Fusaraium oxysporum tomato respectively. 19.61% showed zone of inhibition against
R. solani cotton, 11.76% against R. solani rice and 23.53% against Fusarium
oxysporum tomato respectively. Further quantitative studies were made and these zones
of inhibition were measured. In R. solani cotton, the zone was maximum (2276.5 mm2)
with AH2 and minimum (141.3 mm2) with AM1. Similarly, in R. solani rice, the zone
of inhibition was maximum (1243.44 mm2) with AVK42 and minimum (120.5 mm2)
with AR4 and in Fusarium oxysporum, maximum (1004.8 mm2) with HT54 ii and
minimum (164.05 mm2) with 103. Further, various studies were done to isolate,
evaluate and characterize the antimicrobial substance responsible for this activity. The
antimicrobial substance responsible for the antagonistic activity was found to be
extracellularly produced and it was not thermostable. TLC assays were done to confirm
the production of antifungal and antibiotic compounds taking Pseudomonas as
standard. The invitro results were further checked in pothouse conditions on three
crops, cotton, guar and tomato respectively. Increase in percent germination was
observed. Maximum percentage of disease index (80.36 % and 93.75% on 60th day)
was observed with R. solani cotton and R. solani rice check respectively while
minimum disease index was seen in case of 103DS (16.67 %) in R. solani cotton and
(2.5%) with 103DB in R. solani rice in cotton crop. Similarly in guar crop, maximum
percentage of disease index (95.24% and 85.93% on 60th day) was observed with R.
solani cotton and R. solani rice check respectively while minimum disease index was
seen in case of AH2 (2.5%) in R. solani cotton and (13.29%) with AR4 in R. solani
rice. Further in case of tomato, maximum disease index (85 % on 60th day) was
observed in control Fusarium oxysporum check and was negligible in strains HT57,
AP4, AVK42, AVK51, 103, AH2 and 103DS. The disease was completely controlled
by these selected isolates/mutants.
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Keywords
Diseases, Planting, Fungi, Bacteria, Cotton, Pathogens, Biological control, Vegetables, Rice, Azotobacter