“VARIABILITY STUDIES ON Pyricularia grisea [(Cooke) Sacc.] INCITANT OF BLAST DISEASE IN FINGER MILLET AND ITS MANAGEMENT”
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Date
2024-05-06
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Acharya N G Ranga Agricultural University
Abstract
The study was under taken with an aim to know the variability among isolates of
Pyricularia grisea causing blast disease in finger millet. Studies were carried out on
survey of blast disease to identify the hotspots in major finger millet growing areas of
Andhra Pradesh, variability of isolates using cultural, morphological and molecular
characteristics and evaluating the bacterial bio-control agents and fungicides against
pathogen under in vitro. Efforts were made to identify the promising lines for leaf, neck
and finger blasts and knowing suitable weather conditions for occurrence of disease.
Attempts were also made to manage the disease with biocontrol agent P. fluorescence,
fungicides and their integration.
Survey was conducted during Kharif 2020 and Kharif 2021 in seven major
finger millet growing districts of Andhra Pradesh. The highest mean blast disease
incidence of 56.06% was recorded in Vizianagaram district. The lowest mean disease
incidence of 7.85% was recorded in Prakasam district. Regarding mandals, the highest
mean blast incidence of 56.59% was recorded in Salur mandal of Vizianagaram district
in the range of 53.86 to 59.20% during 2020 and 52.35 to 59.65% during 2021 and
lowest incidence of 7.36% with the range of 5.02 to 9.01% and 4.65 to 9.78% was
noticed in Racherla mandal of Prakasam district during 2020 and 2021 respectively.
The blast samples were collected from different locations of Andhra Pradesh
and a total of 20 monoconidial isolates of Pyricularia grisea were isolated.
The variability in cultural characteristics viz., colony colour, growth pattern,
elevation (flat/elevated growth), sectored or non-sectored, zonations and wrinkle
formation were studied among the isolates of P. grisea isolates on Oat Meal Agar
medium. Efforts were made to study radial growth sporulation of virulent P. grisea
isolate (VIZ-1) in different cultural conditions viz., different media and light conditions.
Good amount of sporulation was observed in observed in Finger millet Leaf extract
Agar (FLA) medium with 1.81 × 105
ml at 5 days after inocultion followed by OMA
with 1.68 × 105
ml at 7 days after inoculation. No significant difference was observed
among three light conditions i.e. light (1.07 × 105
), dark (0.87 × 105
) and light+dark
(0.73 × 105
). Morphological variability among P. grisea was studied through conidial
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morphology. Among the isolates, the overall size of the conidia was in the range of
20.74-23.01 μm × 7.00-9.16 μm (Length × Width).
The molecular variability of P. grisea isolates was studied using 25 SSR
markers, of which seven were polymorphic. The genetic diversity was ranged from
0.180 (MGM 437) to 0.742 (Pyrms 63) with an average of 0.491. Dendrogram using
Neighbor Joining (NJ) resulted in formation of three mega clusters in which cluster I
was further sub grouped into sub-cluster IA, which includes eight isolates and sub cluster IB contains one. Cluster II was further sub grouped into sub-cluster IIA, which
includes six isolates and sub-cluster IIB includes only one isolate. However, cluster III
was further divided into sub cluster IIIA which includes three and IIIB includes only
one isolate.
The RAPD analysis revealed that, out of 8 RAPD primers, 7 primers produced
polymorphic alleles which were selected for genetic diversity analysis. A total of 84
reproducible alleles with an average of 12 fragments per primer were produced using 7
RAPD primers. All the markers displayed polymorphic alleles. Of the total alleles (84),
one allele (OPA-07) was monomorphic with 15.38% monomorphism and 84.61%
polymorphism which contains two monomorphic bond with PIC value of 0.2874.
Whereas 6 primers produced 100% polymorphism with PIC value ranged from 0.1769
to 0.3429 and total number of polymorphic bands were ranged from 8 to 14.
Dendrogram constructed to reveal the pattern of relatedness among twenty P.
grisea isolates using DARwin 6 software on the basis of RAPD polymorphism. Cluster
I is further divided into sub-cluster IA which consisting of nine isolates Sub-cluster IB
of with two isolates. Cluster II further divided into cluster IIA which consisting of four
isolates and sub-cluster IIB contains only one isolate. However, cluster III further
divided into sub-cluster IIIA which contains three isolates and sub-cluster IIIB contains
only one isolate.
A total of 23 bacterial bio-control agents were isolated from rhizospheric soil of
healthy finger millet plants and three isolates were collected from ARS, Vizianagaram
for in vitro studies. Bacterial bio-control agents were evaluated for their antagonistic
effect on P. grisea under in vitro conditions. Results revealed that, maximum inhibition
of mycelium growth (79.54%) was noticed in BVP-1isolate and least mycelial
inhibition was noticed in BJR (11.30%) isolate.
Studies on In vitro evaluation fungicides against the pathogen revealed that
Tricyclazole 75% WP, Carbendazim 50% WP and Tebuconazole 50% + Trifloxystrobin
25% WG inhibited the mycelial growth completely. Compatibility studies of fungicide
and bio-agent revealed that Tebuconazole 50% + Trifloxystrbin 25% WG and
Carbendazim 50% WP at all concentrations were found to be compatible with zero per
cent inhibition of bacterial bio-control agent.
74 lines of finger millet including local check VR 708 were screened for their
resistance against blast in field conditions. Results showed that for leaf blast five lines
were found as highly resistant, 31 lines found as resistant, 23 lines were recorded as
moderately resistant and 15 lines were found to be susceptible. For neck blast, 30 lines
were recorded as resistant, 29 lines shown moderately resistant, 15 lines were reacted as
susceptible. Out of 75 lines screened, 20 lines showed moderate resistance, 41 lines
with susceptible reaction and 14 lines including VR 708 showed highly susceptible
reaction to finger blast incidence.
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Correlation and regression analysis of weather parameters with disease
development revealed that blast disease severity was shown to be higher during the
early planting window, possibly due to comparatively high relative humidity, rainfall
and a greater number of rainy days, all of which favor disease development.
The effective fungicides and potential bacterial bio-control agent were used in
integrated disease management of finger millet blast at S.V. Agricultural College,
Tirupati and ARS, Vizianagaram during Kharif 2021, the treatment T7 and T8 were
found effective for leaf, neck and finger blast with yield.