Pathogenicity of rice blast isolates (Pyricularia oryzae) in irrigated lowland of Bangladesh.

Rice blast poses a significant threat to food security in Bangladesh, particularly in irrigated lowland (boro rice), which constitutes over 50% of the country's total rice production. While using resistant varieties is an effective method to control rice blast, developing durable resistance is challenged by the pathogen's high variability. To address this, the current study examined the distribution of rice blast reaction types in the major rice‐growing ecosystem of Bangladesh, the irrigated lowland. Two surveys were conducted and 80 blast isolates were evaluated for pathogenicity against differential varieties (DVs). The results revealed that the high frequency of virulence (over 80%) for blast resistant genes, such as Pib, Pit, Pia, Pik‐s, Pi12(t), Pi19(t) and Pi20(t), whereas Pish, Pik‐m, Pi1, Pik‐h, Pi9 and Pita‐2 genes had the least virulence frequency. These low virulence frequency genes demonstrated promising potential for the development of blast resistant varieties in Bangladesh. The isolates were further categorized into two distinct cluster groups based on their reaction patterns to DVs, with theones coming from the eastern region predominantly in Cluster I, while the ones from the northern regions belonged mainly to Cluster II. Additionally, the isolates were classified based on five reaction types, namely U, i, k, z and ta, following a new designation system. Among these, U63, i0, k100, z06 and ta403 were the most dominant reaction types. Although these reaction types were prevalent across Bangladesh, their distribution frequency varied in different major rice‐growing regions. Furthermore, the study observed that early maturing varieties in the irrigated lowland ecosystem were highly susceptible to blast. The findings of this study will be crucial for developing a comprehensive and long‐lasting blast protection system in Bangladesh, focusing on broad‐spectrum resistance strategies. [ABSTRACT FROM AUTHOR]