4. Morphological variability among the pyricularia oryzae isolates causing rice blast disease in South Western Region of Bangladesh

Rice is a staple food crop for majority of human population worldwide. Significant grain yield losses are reported due to blast disease caused by Pyricularia oryzae across all rice growing areas of the world. Though, presently available blast management strategies reduce disease significantly but blast epidemics are still common, thereby causing devastating yield losses. The present study was aimed at determining the variability among the Pyricularia oryzae isolates. Leaf blast samples were collected from South-Western regions of Bangladesh the causal pathogen was isolated following tissue planting method in the Plant Pathology Laboratory of Agrotechnology Discipline, Khulna University, and Khulna, during September 2020 to September 2021. Morphological variability was determined based on nine morphological components like as front mycelial color, reverse mycelial color, growth behavior, length of conidia (μm), width of conidia (μm), conidial color, radial growth at 12 days (mm) after incuation, radial growth at 14 days (mm) after incuation and radial growth at 16 days (mm) after incuation. Seven types of mycelial colors were recorded. These were- Light brown, Deep brown, Light gray, Olivaceous grey, Grey, Deep grey and Black. Two types of growth behavior- Smooth and Rough were present in P. oryzae isolates. Two types of conidial color- Blackish and Transparent were also observed among the 19 isolates. Cluster analysis considering nine morphological components showed five distinct groups. Three isolates were placed in each cluster I and III, cluster II contains seven isolates, cluster IV contained five isolates and cluster V contained only one isolate (PO-11). PO-11 showed distinct morphological variations among the 19 isolates, which was originated from AEZ-11. PCA biplot demonstrated a high range of variation and showed with high negative correlation between two groups of variable. One consisted of conidial length, conidial breadth and growth behavior and another consists of reverse mycelial colony color, front mycelial colony color, conidial color, radial growth at 12 days, 14 days and 16 days after incubation. Among the nine morphological components, front and reverse mycelial color, growth behavior and conidial length played more than 80% role in generating variation among the nine tested components.

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