Comparative evaluation on chemical composition and in vitro anti-Fusarium activity of solvent extracts of Zingiberaceae rhizomes from Indonesia

Fusarium oxysporum f.sp. cubense (Foc) is a fungus that not only causes disease while bananas are being grown, but it also causes begetting after bananas are harvested, which limits the production of bananas. Zingiberaceae plants contain a high number of extractable secondary metabolites that are regarded to have effective antifungal activities. However, in order for the compounds to be suitable for use, they must be tested by modifying the polarity in the extracting solvent. In this study, four Zingiberaceae species were examined, namely Zingiber officinale, Curcuma longa, C. zanthorrhiza, and Alpinia galanga. The extraction of rhizomes of each plant was accomplished by using solvents with distinct polarity index (PI) viz. water (PI 9.0); a mixture of 50% water and 50% ethanol (PI 7.1); ethanol (PI 5.2); and n-hexane (PI 0.0). The anti-Fusarium evaluation of these 16 extracts was carried out in vitro by implementing the pour plate method in potato dextrose agar (PDA). Our results showed that the C. zanthorrhiza n-hexane extract possessed the greatest antifungal activity among other extracts. The fungal inhibition ability of the extracts was negatively correlated with the increase in solvent polarity index. In order to comprehend our understanding of the antifungal activity, the chemical compositions of each extract were identified through non-targeted Gas Chromatography–Mass Spectrometry (GC-MS), showing the main components of the n-hexane extracts were terpenes and terpenoids. Particularly, C. zanthorrhiza n-hexane extract contained, with the percentage of abundance in parentheses, germacrene B (22.99%), β-farnesene (14.72%), curzerene (10.87%), 2-bornanone (9.60%), α-curcumene (9.32%), zingiberene (8.30%), β-curcumene (6.36%), β-elemene (5.31%), caryophyllene (3.36%), cedrene (2.73%), α-bergamotene (1.36%), and humulene (0.20%). As conclusion, this crude extract or its pure chemical constituents have potential application as biofumigant to control Foc in postharvest banana.