MSc

The study entitled "Etiology and management of sheath rot disease of rice"
was conducted at Department of Plant Pathology, College of Agriculture Vellayani
and Rice Research Station, Moncompu during 2020-2022, with the objective to isolate
and characterize the pathogen associated with sheath rot disease of rice and evaluate
the efficacy of the available Bacillus sp.and commercial fungicides against sheath rot
disease of rice.
Purposive sampling survey conducted in four rice growing districts of Kerala
during 2021-2022 to collect the sheath rot infected panicles and to access the disease
incidence (DI) and disease severity (DS). Among the surveyed locations, maximum DI
(49.23 per cent) and DS (46.32 per cent) were recorded from Neelamperoor and
Palakkad. S. oryzae was isolated from the collected specimens; a total of five pure
cultures of S. oryzae (Isolate I1 to Isolate I5) were obtained and Koch's postulates were
proved for all the isolates in rice var. Uma.
All the S. oryzae isolates were screened for its virulence and pathogenicity in
rice var. Uma. The isolate I5, from Thrithala produced the symptom within 24 h of
artificial inoculation. On 4th day of artificial inoculation, isolate I5 recorded a
maximum lesion size of 2.50 cm; and thus, concluded as the most virulent isolate.
The cultural characters of these 5 isolates were whitish orange with some radial
foldings and morphological characters of hyphae was septate and whitish orange in
color and spores single celled and cylindrical in shape. Average size of the spore was
5.53 x 1.66 µm.
Dual culture assay of Bacillus sp. B15, Bacillus sp. B17, Bacillus sp. B33,
Bacillussp. B42 and Pseudomonasfluorescens(PN026) in potato dextrose agar (PDA)
medium indicated that the beneficial endophytic bacteria significantly inhibited the
growth of the pathogen through multiple antagonistic properties. Maximum growth
inhibition of S. oryzae (70.95 per cent) by P. fluorescens (PN026) followed by
Bacillus sp. B17 (64.45 per cent) and Bacillus sp. B 42 (50.95 per cent) were observed
on 12 th day of dual culturing.
Among the four commercial fungicides tested in vitro, trifloxystrobin
25%+tebuconazole 50 % 75 WG (400ppm), propineb 50 WP (2500ppm) and
hexaconazole 5EC (2000ppm) completely inhibited (100%) the sheath rot pathogen
compared to copper hydroxide 77 WP (2000ppm) which inhibited the growth of the
sheath rot pathogen by 86.42% per cent. Considering the overall performance,
recommended doses of trifloxystrobin 25%+tebuconazole 50 % 75 WG (400ppm),
propineb 50 WP (2500ppm) and hexaconazole 5 EC (2000ppm) were more effective
against sheath rot pathogen.
The isolation of DNA from sheath rot pathogen was carried out by using CTAB
(cetyltrimethyl ammonium bromide) method of DNA isolation. Quality and quantity
of sample DNA were 1.73 and 60 µg ml-1
. Size of the amplicon is 608bp. This sheath
rot associated pathogen was identified from Rajiv Gandhi Centre for Biotechnology
(RGCB), Thiruvananthapuram as Sarocladium oryzae through molecular
characterization (GenBank Accession no. OP716814). This sheath rot pathogen was
used for further studies.
Pot culture experiment was conducted for screening rice varieties (20 numbers)
for resistance to sheath rot pathogen. Artificial inoculation was done at panicle initiation
stage. Aathira and Shreyas showed tolerant reaction to sheath rot disease whereas Uma
variety showed the highest susceptibility nature.
The biocontrol agents and fungicides were evaluated in the field against sheath
rot disease of rice during Kharif 2022 at RRS, Moncompu. Management of disease
before panicle emergence is very much essential. Prophylactic application of talc-based
formulation of Bacillus sp. B15, Bacillus sp. B17, Bacillus sp. B33, Bacillus sp., B42,
B 15+ B17+ B 33+ B 42 consortium and Pseudomonas fluorescens (PN026) as seed
treatment (10g kg-1
) + soil application (1kg/acre) + foliar spray (20g L-1
of water at
booting stage) for the management of sheath rot disease of rice and thereby improving
the yield. Among all the bioagent treatments, the application of B 15+ B 17+ B 33+ B
42 consortium showed more efficacy nature for the management of sheath rot disease
of rice and improving the yield.
Four commercial fungicides viz., copper hydroxide 77 WP @ 2 g L-1
,
trifloxystrobin25%+tebuconazole 50 % 75 WG @ 0.4 g L
-1
, propineb 50 WP @ 2.5 g
L
-1
and hexaconazole 5 EC@2 ml L-1 were given as foliar spraying at booting stage.
Among all the fungicides tested in the field, trifloxystrobin 25%+tebuconazole 50 %
75 WG @ 0.4 g L
-1
and hexaconazole 5 EC@ 2 ml L-1
applied as foliar spraying were
significantly superior in reducing the disease and increasing the yield followed by
propineb 50 WP @ 2.5 g L-1
and copper hydroxide 77 WP @ 2 g L-1
. Benefit cost ratio
was also more in case of B 15+ B 17+ B 33+ B 42 consortium and trifloxystrobin
25%+tebuconazole 50 % 75 WG @ 0.4 g L-1
.
Thus, the present study revealed that sheath rot of rice could be managed by
using Bacillus sp. B 15+ B 17+ B 33+ B 42 consortium as seed treatment (10g kg-1
) +
soil application (1kg/acre) + foliar spray (20g L-1
of water at booting) and commercial
fungicide, trifloxystrobin 25%+tebuconazole 50 % 75 WG @ 0.4 g L
-1
and hexaconazole
5 EC at 2 ml L
-1
. The results may be subjected to multi-location and multi- seasonal
field trails before recommendation. The compatibility of Bacillus sp. consortium with
new generation fungicides and the residue of fungicides in grain may further be studied.