Survey on rice blast in two selected districts of Bangladesh and variations of Magnaporthe oryzae in different culture media

Abstract

Rice blast, caused by Magnaporthe oryzae, is one of the most devastating diseases of rice worldwide, particularly in South and Southeast Asia. This study aimed to assess the incidence of rice blast in two major rice-growing districts, Cumilla and Brahmanbaria, of Bangladesh, and to evaluate the morphological variation of the causal pathogen under different culture media. Field surveys were conducted during the Boro season 2020-2021, and disease severity was recorded using standard disease scoring scales. Infected samples were collected and used to isolate M. oryzae in the laboratory. A total of 6 isolates of M. oryzae were cultured on Potato Dextrose Agar (PDA), Oatmeal Agar (OMA), Potato Sucrose Agar (PSA), Rice Flour Yeast Agar (RFYA), and their morphological features were compared. Significant differences in colony color, surface texture, growth rate, and conidial shape were observed among the media. The highest mycelial growth was recorded on RFYA media, which is 90 mm with grayish white colony color and a rough, cottony, irregular surface structure. At the same time, distinct pigmentation was prominent on OMA and other media. These findings enhance understanding of rice blast distribution in Bangladesh and the media-dependent morphological traits of M. oryzae, which can aid in future diagnostics and disease management strategies.