Natural Product Citronellal can Significantly Disturb Chitin Synthesis and Cell Wall Integrity in Magnaporthe oryzae

Natural products are often favored in the study of crop pests and diseases. Previous studies have shown that citronellal has a strong inhibition effect on Magnaporthe oryzae. The objective of this study was to clarify its mechanism of action against M. oryzae.

Firstly, the biological activity of citronellal against M. oryzae was determined by direct and indirect methods, and the results show that citronellal had a strong inhibition effect on M. oryzae with EC₅₀ values of 134.00 mg/L and 70.48 μL/L air, respectively. Additionally, a preliminary study on its mechanism of action was studied. After citronellal treatment, electron microscopy revealed that the mycelium became thin and broken; scanning electron microscopy revealed that the mycelium was wrinkled and distorted; and transmission electron microscopy revealed that the mycelium cell wall was invaginated, the mass wall of mycelium was separated, and the organelles were blurred. The mycelium was further stained with CFW, and the nodes were blurred, while the mycelium was almost non-fluorescent after PI staining, and there was no significant difference in the relative conductivity of mycelium. In addition, chitinase was significantly enhanced, and the expression of chitin synthesis-related genes was 17.47-fold upregulated. Finally, we found that the efficacy of citronellal against the rice blast was as high as 82.14% according to indoor efficacy tests.

These results indicate that citronellal can affect the synthesis of chitin in M. oryzae and damage its cell wall, thereby inhibiting the growth of mycelium and effectively protecting rice from rice blasts.