STUDIES ON BIOLOGICAL CONTROL POTENTIAL OF NATIVE BACILLUS SPP. AGAINST RHIZOCTONIA SOLANI KUHN. CAUSING RICE SHEATH BLIGHT
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Date
2024-05-06
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Acharya N G Ranga Agricultural University
Abstract
A roving survey was conducted during, rabi, 2020-2021 in Chittoor and
Nellore districts of Andhra Pradesh to assess the disease severity of sheath blight
disease in rice. The disease severity ranged from 6.11 to 13.44%. Rice sheath
blight pathogen R. solani was isolated from the diseased samples obtained during
survey. Its pathogenicity was proved by using mycelial ball insertion technique.
A total of 26 native Bacillus spp were isolated from the rhizoplane soils of
rice crop of Chittoor and Nellore districts and their antagonistic efficiency was
tested using dual culture technique. Among the isolates, NB13 showed maximum
antifungal efficiency with 86.15% followed by CB10 (81.60%) and CB4 (75 %).
Maximum inhibition of sclerotial germination was observed in CB4 (98.42%)
followed by NB13 (97.2%) and CB10 (96.36%) and maximum per cent of lysis
of sclerotia was observed in CB10 isolate (100%) followed by CB4 (98.14%)
and NB13 (95.55%). Those isolates CB4, CB10, NB13 recorded maximum
mycelial inhibition, sclerotial inhibition and sclerotia lysis which are
significantly on par.
Cultural characters viz., colony shape, colour, size, surface, margin,
elevation and time of colony appearance of the potential Bacillus isolates were
recorded. Among all isolates NB4, NB13, CB10 isolates produced irregular,
white, large colonies with rough surface, lobate margins, flat elevation and
formed colonies with 48h after inoculation. CB4 produced irregular, white, large
colonies with rough surface, filamentous margins and formed colonies with 48h
after inoculation.
Out of ten potential isolates tested for biochemical tests, all isolates
showed positive reaction to gram staining, endospore staining, motility test and
catalase test, whereas only seven isolates showed positive reaction to anaerobic
growth, six isolates showed positive reaction to oxidase test and three isolates
showed positive reaction to nitrate reduction test.
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16S r DNA sequence analysis revealed that the NB4, NB13, CB4 and
CB10 have close similarity with Bacillus subtilis.
Out of the 10 potential isolates maximum chitinase activity (maximum
halo zone diameter (2.6 cm) and chitinolytic index (3.13) and oxalate oxidase
enzyme activity (maximum halo zone diameter 2.35cm) was observed in isolate
CB10.
A total of ten potential isolates were screened for PGPR characteristics.
All the isolates were positive to siderophore production, phosphate solubilization
activity, of which CB10 isolate recorded highest siderophore index, maximum
zinc carbonate solubilization index and efficiency and NB13 recorded maximum
IAA production, PSI and PSE% and also produced maximum ZSI and ZSE %
for zinc phosphate, CB4 recorded highest potassium solubilizing index and
efficiency and five isolates were positive for HCN production, four isolates for
organic acid production, while isolate CB10 was produced maximum ACC
(58nm-α-ketobutyrate mg-1h
-1
).
All the ten potential isolates significantly increased seed germination,
seedling growth (root &shoot length) and vigor index of rice seedlings when
compared to control by paper towel method. Among these highest vigor index
was recorded NB13 (2683.66), followed by CB10 (2380.70), CB4 (2214.83)
which are significantly on par.