Isolation and Morpho-Molecular Characterization of Alternaria spp. Causing Grey Leaf Blight of Mustard in Different Regions of Bangladesh

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 responsible for grey blight disease of mustard in different regions of Bangladesh. The experiment was 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. Diseased mustard leaves displaying characteristic symptoms were collected from eight distinct mustard-growing districts in Bangladesh, namely Jashore, Khulna, Satkhira, Dhaka, Manikganj, Tangail, Sirajganj, and Dinajpur. Fungal DNA was extracted from pure cultures of Alternaria, and PCR amplification was conducted using ITS primers designed to yield 700 bp fragments. Morphological characterization revealed considerable variations among Alternaria species, including differences in radial mycelial growth, colony color, shape, texture, subsurface color, zonation, conidia production, and sporulation time. Pathogenicity tests confirmed the pathogenic nature of all Alternaria isolates. Molecular analysis using ITS regions demonstrated a 99% similarity of the nucleotide sequences with existing sequences in the NCBI database, closely related to Alternaria brassicae, Alternaria brassicicola, and Alternaria alternata. Three species of Alternaria (A. brassicae, A. brassicicola, and A. alternata) were identified from grey blight-infected mustard leaves. Additionally, variations were observed in the number of conidia, longitudinal septation, transverse septation, conidial length, and breadth among the different isolates. The study highlighted the close genetic relationship among the Alternaria isolates and their association with grey blight disease in mustard. These findings contribute valuable insights into the genetic diversity and pathogenicity of Alternaria species in Bangladesh's mustard-growing regions. Such knowledge can be instrumental in developing effective disease management strategies to mitigate yield losses in this crucial oilseed crop.