Abstract:
Mustard (Brassica spp.) is the most important oil seed crop in Bangladesh and the major
constraint is grey blight disease which caused significant yield losses. The prime aim of the study
was to characterize the Alternaria species on the basis of morpho-molecular variation and
integrated management of the grey blight disease. The present study was carried out in
combination of six sequential experiments. The experiments were conducted in Molecular
Biology and Plant Virology Laboratory, Department of Plant Pathology, Sher-e-Bangla
Agricultural University, Dhaka and Plant Pathology Laboratory, Bangladesh Agricultural
Research Institute (BARI), Joydebpur, Gazipur. For characterization study, fungal DNA was
extracted from the pure culture of Alternaria and PCR amplification was done using the ITS
primer which designed to amplify at 700 bp. For the management study to evaluate the
effectiveness of selected bio-agent, chemical fungicides, botanicals and their combined effects
were assessed. In total 14 treatments including control were considered viz. T
1
=
Trichoderma harzianum suspension, T
3
= Autostin 50 WDG, T
4
= Control, T
2
= Rovral 50 WP, T
5
= Dithane
M-45, T
6
= Amistar Top 325 SC, T
7
= Neem leaf extract, T
8
= Allamanda leaf extract, T
9
= Lantana
leaf extract, T
10
= Datura leaf extract, T
11
= Neem leaf extract+ Rovral, T
12
= Datura leaf extract +
Amistar Top, T
13
= Lantana leaf extract + Dithane M- 45 and T
14
= Allamanda leaf extract +
Autostin. From the morphological characterization of Alternaria species, it was found that the
highest radial mycelial growth (43 mm) was recorded in Manikganj isolate and the lowest (18.13
mm) in Satkhira isolate at 14 DAI and others morphological characters were varied significantly.
All Alternaria isolate was found to be pathogenic in nature that confirmed in the pathogenicity
test. From the molecular characterization study, the nucleotide sequences of Alternaria isolates
were showed 99% similarity with the existing nucleotide sequences and closely related to isolates
of Alternaria brassicae, Alternaria brassicicola and Alternaria alternata that globally found in
GenBank data based. Among the treatments, there was no radial mycelial growth of Alternaria
was recorded in T
4
(Rovral 50 WP), T
6
(Dithane M-45) and T
11
(Neem leaf extract+ Rovral) at all
observations. From the results of field management study, it was observed that all the treatments
showed significant effect on different assayed parameters. In case of botanicals, the lowest disease
incidence (%), disease severity (%), disease severity index (%) and pod infection (%) was found
in T
9
treatment (Lantana leaf extract) which was 65.05%, 28.89%, 37.96% at 70 DAS respectively
and 13.79%, at 75 DAS. In case of chemicals, the lowest disease incidence (%), disease severity
(%), disease severity index (%) and pod infection (%) was found in T
5
treatment (Dithane M-45)
which was 55.91%, 22.09%, 32.16% at 70 DAS, respectively and 6.72% at 75 DAS. In case of
combined treatments, the lowest disease incidence (%), disease severity (%), disease severity
index (%) and pod infection (%) was found in T
13
treatment (Lantana leaf extract + Dithane M45)
which
was
59.14%,
26.32%,
38.20%
at
70
DAS,
respectively
and
12.30%
at75
DAS.
From
the
findings
on different parameters studied in both management experiments, Dithane M-45,
Lantana leaf extract and their combined treatment could be used in further field trials and then
may be recommended for management of grey blight mustard.