Temperature‐Dependent Variation in Appressorium Development and Pathogenicity Reveals Strain‐Specific Thermotolerance in Pyricularia oryzae

ABSTRACT

Temperature is a key environmental factor influencing the development and severity of plant diseases. In the rice blast pathogen Pyricularia oryzae , successful infection depends on appressorium formation, a process that is strongly influenced by temperature. In this study, we investigated strain‐specific responses to elevated temperature through phenotypic characterization, pathogenicity assays and transcriptomic analysis. Appressorium formation was strongly temperature‐dependent, with optimal development at 25°C and near‐complete inhibition at 35°C. At 30°C, strains showed contrasting responses, allowing classification into thermotolerant and thermosensitive groups based on their capacity to maintain appressorium formation. Thermotolerant strains retained pathogenicity at elevated temperature, whereas thermosensitive strains exhibited variable effects on pathogenicity. Time‐course analyses further demonstrated that appressorium development in one thermosensitive strain was delayed rather than permanently inhibited under elevated temperature. Transcriptomic analysis revealed that thermotolerant strains exhibited relatively limited changes in gene expression, while thermosensitive strains showed extensive transcriptional responses, particularly in metabolic and transport‐related pathways. Chemical complementation experiments further indicated that thermosensitive strains differed in their responses to surface‐associated cues under heat stress, which may contribute to reduced appressorium formation. These findings indicate that thermotolerance in P. oryzae is associated with the maintenance of infection‐related development under elevated temperature and highlight the potential impact of climate warming on the behaviour of rice blast populations.