Chemical Constituents and Antimicrobial Activity of a Ganoderma lucidum (Curtis.) P. Karst. Aqueous Ammonia Extract.

Mushroom extracts have shown potential as a source of new antimicrobial agents. This study investigates the chemical profile of an aqueous ammonia extract obtained from the carpophores of Ganoderma lucidum , which grows on Quercus ilex trees, and explores its valorization as a biorational. The major chemical constituents of the extract, identified through gas chromatography-mass spectrometry, include acetamide, oleic acid, 1,2,3,4-butanetetrol, monomethyl azelate, undecane, and palmitic acid. The anti-oomycete and antifungal activity of G. lucidum extract was evaluated against Phytophthora cinnamomi , the primary threat to Quercus spp. in the dehesa biome, as well as three Botryosphaeriaceae fungi. In vitro tests revealed minimum inhibitory concentration (MIC) values of 187.5 μg·mL -1 against P. cinnamomi and 187.5-1000 μg·mL -1 against the fungi. Furthermore, conjugation of the G. lucidum extract with chitosan oligomers (COS) synergistically enhanced its antimicrobial activity, resulting in MIC values of 78.12 and 375-500 μg·mL -1 against P. cinnamomi and the fungi, respectively. These MIC values are among the highest reported to date for natural products against these phytopathogens. Subsequent ex situ testing of the COS- G. lucidum conjugate complex on artificially inoculated Q. ilex excised stems resulted in high protection against P. cinnamomi at a dose of 782 µg·mL -1 . These findings support the potential utilization of this resource from the dehesa ecosystem to protect the holm oak, aligning with sustainable and circular economy approaches.