MOLECULAR CHARACTERIZATION OF ALTERNARIA SPECIES AND INTEGRATED MANAGEMENT OF GREY BLIGHT DISEASE OF MUSTARD

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.