Antifungal and Antioomycete Activities of a Curcuma longa L. Hydroethanolic Extract Rich in Bisabolene Sesquiterpenoids

Curcuma longa, known for its anti-inflammatory, antioxidant, and antimicrobial properties, has been a staple in traditional medicine for centuries. In the pursuit of natural alternatives to synthetic preservatives, the extracts of C. longa have garnered attention for their efficacy in extending shelf life and preventing the spoilage of diverse agricultural products. This study aims to assess the antifungal and antioomycete activities and plant protection capabilities of a hydroethanolic C. longa extract as a natural product against crop pathogens. The phytochemical profile of the C. longa extract was elucidated through gas chromatography-mass spectrometry. The extract exhibited a richness in bisabolene sesquiterpenoids, notably (+)-beta-turmerone, alpha-turmerone, (+)-(S)-ar-turmerone, and included minor phytoconstituents, such as alpha-atlantone, gamma-curcumene, zingiberene, isoelemicin, and gibberellin A3. Radial growth inhibition assays demonstrated the C. longa extract's effectiveness against various phytopathogenic fungi, including Botrytis cinerea, Colletotrichum acutatum, and Diplodia corticola, as well as the oomycetes Phytophthora cactorum and Phytophthora cinnamomi. In ex situ tests, the C. longa extract demonstrated remarkable protection capabilities for Malus domestica excised stems against P. cinnamomi-induced necrosis. Furthermore, the C. longa extract exhibited non-toxicity towards lettuce seed germination and did not impact early lettuce seedling growth, indicating its safety for crop protection. These findings contribute to expanding the potential applications of C. longa as an antimicrobial agent, particularly for safeguarding economically significant trees against the destructive oomycete P. cinnamomi.