Discovery of Tropolone Stipitaldehyde as a Potential Agent for Controlling Phytophthora Blight and Its Action Mechanism Research

The fermentation of endophytic Nigrospora chinensis GGY-3 resulted in the isolation of tropolone stipitaldehyde (1), which exhibited broad-spectrum inhibition activity against fungi and bacteria, especially against Phytophthora capsici, with an EC₅₀ value of 0.83 μg/mL and Xanthomonas oryzae pv. oryzicola, with a minimum inhibitory concentration value of 4.0 μg/mL. The in vitro and in vivo assays demonstrated that 1 had a significant protective effect on P. capsici. Furthermore, 1 inhibited the spore germination of P. capsici and damaged the plasma membrane structure. As observed by SEM and TEM, after exposure to 1, mycelia exhibited swelling, shrunken, branch-increasing phenomena, cell wall and membrane damage, and disordered content. Transcriptome analysis revealed that 1 might affect starch and sucrose metabolism and fatty acid biosynthesis by suppressing the expression of genes relevant to cell wall synthetases and cell membrane-associated genes. These findings indicate that 1 may be a potential agrochemical fungicide for controlling phytophthora blight.