Morphological and molecular identification of Pyricularia oryzae causing blast disease on rice (Oryza sativa)

Aims: Rice (Oryza sativa) is one of Malaysia's most significant crops. Rice blast caused by Pyricularia oryzae is one of the most serious diseases of Oryza sativa, causing significant damage to the Malaysian rice crop and impacting productivity. This study was carried out to isolate and characterize phytopathogenic fungal isolates associated with rice blast collected in a paddy field in Alor Setar, Kedah, Malaysia.Methodology and results: Morphological characterization of seven fungal isolates obtained showed thin, white, and grayish green mycelia and the reverse colony was light yellow to brown. The fungal isolates produced two-septate pyriform (pear-shaped) conidia with solitary, unbranched and light brown conidiophores. Pathogenicity tests of all isolates on rice leaves revealed diamond-shaped symptoms with a grayish center and brown edge. All isolates showed similar morphological and pathogenicity characteristics; thus, a representative isolate was further identified through DNA sequencing and phylogenetic analysis of the internal transcribed spacer (ITS) region for species confirmation. Based on DNA sequences of ITS and phylogenetic analysis, the representative isolate was confirmed as P. oryzae.Conclusion, significance and impact of study: Seven isolates morphologically identified as Pyricularia sp. were tested as pathogenic by causing rice blast disease. Representative isolate P2 (USM-PD1) was confirmed to be P. oryzae by DNA sequencing and phylogenetic analysis of the ITS region. This study provides information on the etiology and symptomatology of rice blast disease caused by P. oryzae USM-PD1 that can be applied to diagnose and mitigate the threat posed by this plant pathogen for the disease management.