High Illuminance and Low Temperature Promote Perithecial Production of the Green Bristlegrass Blast Fungus Magnaporthe oryzae

Sexual reproduction of the ascomycetous fungus Magnaporthe oryzae is reported to be regulated by illuminance and temperature, but their temporal interaction during perithecial production remains unclear. Here, we performed full-factorial condition transfer assays (illuminance: low/0 lx, medium/1000 lx, or high/5000 lx; temperature: low/19 °C or high/25 °C) using a pair of high-fertility M. oryzae isolates collected from green bristlegrass to characterize sequential and combinatorial effects of illuminance and temperature on perithecial production. We found that perithecial production showed a strong positive correlation with illuminance at 19 °C, and continuous darkness completely abolished their fertility. Early illuminance priming promotes perithecial production in a dose-dependent manner, whereas prolonged initial darkness for over four days results in remarkable reductions in perithecial production. Moreover, pre-transfer at 25 °C promoted perithecial production under 1000 lx or darkness, and post-transfer at 19 °C sustained or enhanced perithecial production. We also found that plates initially cultured at 5000 lx maintain high capacity for perithecial production across most post-transfer environments, especially under the post-transfer condition at 19 °C with over 2000 perithecia per plate. Taken together, our study demonstrates that combinations of high illuminance and low temperature promote perithecial production of the green bristlegrass blast fungus M. oryzae under laboratory conditions, providing alternative insights into the roles of environmental factors in fungal sexual reproduction.