STUDIES ON THE INTEGRATION OF CHEMICAL AND BIOLOGICAL METHODS FOR THE MANAGEMENT OF RICE STEM ROT DISEASE CAUSED BY Sclerotium oryzae Catt.
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Date
2018
Authors
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Acharya N.G. Ranga Agricultural University
Abstract
Stem rot of rice, caused by Sclerotia oryzae Catt. is a serious threat to
rice production in India. Fungicides provide control of this pathogen but also
have ill effects on the environment. In an attempt to develop better integrated
strategies using fungicides and bacterial bio agents for management of stem
rot disease, a total of eight isolates from different localities of Nellore
district were isolated. The isolates of S. oryzae were designated as SO 1, SO
2, SO 3, SO 4, SO 5, SO 6 SO 7 and SO 8. Variability among these isolates
of S. oryzae based on growth rate on PDA and also in utilizing various
carbon sources was assessed using four different growth media. Depending
on the growth rate on PDA medium, these isolates of S. oryzae could be
categorised into four groups. Group 1 had the very fast growing isolate SO
3. Group 2 comprised of four isolates SO 1, SO 4, SO 6 and SO 7 which
were fast growing. Group 3 consisted of the medium growing isolates i.e.
SO 2, SO 8. Group 4 consisted of isolate SO 5 is very slow growing. Among
the growth media tested, PDA was best supported for growth of all isolates
and there was no growth of all the isolates of S. oryzae grown on CDA.
Among the eight isolates, isolate SO 3 which was fast growing with
abundant sclerotial production was selected for further studies. A total of
thirteen antagonistic bacteria were isolated from rhizosphere soil of rice.
Highest inhibition was recorded in case of RRB-2 (74.07%) followed by
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RRB-4 with 70.73% inhibition, RRB-1 with 65.92% inhibition and RRB-3
with 62.22% inhibition. Least inhibition was observed with RRB-12
(31.84%) and with RRB-13 (33.31%). Four of these effective bacterial
antagonists were used for further studies. Thirteen plant extracts, five plant
essential oils and five natural preparation were tested for their bio efficacy
against S. oryzae at different concentrations. The extract (powdered seeds)
of Brassica juncea was found to be the most effective in inhibiting the
growth of S. oryzae (100%) at 20 and 25% concentrations followed by
rhizome extract of Curcuma longa (84.81) at 20% concentration, bulb
extract of Allium sativum (84.44) at 2.0% concentration, leaf extract of
Eucalyptus glubulus (76.29%). The bulb extract of Allium cepa recorded the
least mean inhibition (4.40%) of S. oryzae at 5%. Out of the five essential
oils, lemon grass oil showed 100 % inhibition of the test fungus at all tested
concentrations. Spearmint oil at 1%, 1.5% and 2% concentrations and
eucalyptus oil at 2% and 3% concentrations recorded 100% inhibition in the
growth of S. oryzae. The mustard oil at 0.5% concentration recorded least
inhibition (7.77%) followed by neem oil at 0.5% concentration with 19.25%
inhibition in the growth of S. oryzae. Among the natural preparations,
neemasthra was found to be the most effective in inhibiting the growth of
S. oryzae (55.56%) followed by brahmasthra (49.66%), agniasthra (36.66%)
and jeevamrutham (35.56). The neem seed kernel recorded the least mean
inhibition (2.23%) of S. oryzae at 5000 ppm. Among the fifteen fungicides
tested, Carbendazim, Propiconazole, Hexaconazole, Difenoconazole,
Tebuconazole, Trifloxystrobin + Tebuconazole, Azoxystrobin, Isoprothiolane,
Mancozeb + Carbendazim, Benomyl and Thiophanate-methyl completely
(100%) inhibited the growth of S. oryzae at all concentrations in vitro.
Thifluzamide (0.04%) recorded least per cent inhibition. Twelve fungicides
were tested in vitro for the compatibility with potential biocontrol agents
viz., RRB-1, RRB-2, RRB-3 and RRB-4. Isolate RRB-4 was found to be
most compatible antagonistic bacteria as it has shown highest compatibility
when compared to other isolates. Hexaconazole showed highest compatibility
with all the four isolates followed by propiconazole.
Effective fungicides and antagonistic bacterial isolates in in vitro
studies were evaluated under field conditions. Results of pooled analysis of
Rabi 2016-17 and early Kharif 2017-18 revealed that, among the fungicides,
treatment Hexaconazole recorded lowest PDI. While among the bacterial
antagonists, treatment Root dipping with RRB-4 + foliar spray showed less
PDI after second spray. Hence, these two treatments were selected for
further field trial during Rabi 2017-18 to evaluate the strategies involving
the integration of effective fungicide and bacterial antagonist for the
management of rice stem rot disease. Pooled analysis of the yield data
revealed that the highest grain yield was recorded in Hexaconazole
treatment (7.43 t/ha) followed by Difenoconazole (7.29 t/ha), Tebuconazole
(7.19 t/ha), Root dipping with RRB-4+ foliar spray (6.97 t/ha), Carbendazim
(6.91 t/ha) and Mancozeb + Carbendazim (6.89 t/ha). Least grain yield was
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observed in untreated control (5.22t/ha) followed by Root dipping with
RRB-3+ foliar spray (5.74 t/ha) which were statistically at par with each
other. In case of straw yield, Hexaconazole treatment (7.22 t/ha) recorded
highest straw yield followed by Difenoconazole; 6.88t/ha and Propiconazole;
6.84 t/ha which were statistically at par with each other. Least straw yield
was observed in untreated control (5.47 t/ha). During Rabi 2017-18, the
evaluation of the strategies of integration of effective fungicide
Hexaconazole (0.2%) and the antagonistic isolate RRB-4, results revealed
that, among the seven treatments consisting of different strategies, the
following strategies were found superior.
1. Alternate sprays with hexaconazole and RRB-4 (40.00 PDI;
7.56 t/ha grain yield and 10.26t/ha straw yield).
2. Seedling dip with RRB-4 and two sprays followed by two
sprays with hexaconazole (44.40 PDI, 6.95 t/ha grain yield and
8.53 t/ha straw yield).
3. Two sprays with hexaconazole followed by two sprays with
RRB-4 (48.35 PDI, 7.37 t/ha grain yield and 7.73 t/ha straw
yield).
Description
D5733
Keywords
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