ANTI-PHYTOPATHOGENIC FUNGAL COMPOUNDS FROM THAI PLANTS Alpinia galanga Willd. Mansonia gagei Drumm. AND Melodorum fruticosum Lour.

Abstract

Forty-six Thai plants were preliminarily screened for antiphytopathogenic fungal activity. Three promising plants namely Alpinia galanga Willd. rhizomes, Mansonia gagei Drumm. heartwoods and Melodorum fruticosum Lour. flowers were selected for further study. The CH2Cl2 extracts displayed strong antifungal activity against four fungi: Alternaria porri, Colletotrichum gloeosporioides, Fusarium oxysporum and Phytophthora parasitica. Further separation and isolation were carried out based on bioassay guided. The constituents of A. galangal rhizomes comprised of phenylpropanoids which were identified based on physical properties and spectroscopic evidence as 1ʹ-acetoxy chavicol acetate (ACA), trans-p-coumaryl diacetate, trans-p-hydroxycinnamyl acetate, trans-p-hydroxycinnamaldehyde and two compounds from ACA solvolysis as trans-p-coumaryl alcohol ethyl ether and trans-p-acetoxycinnamyl alcohol. The major constituent in the essential oil from the fresh rhizomes are 1,8-cineole (73%), 2-acetoxy-1,8-cineol (13%) and terpinen-4-ol (3%). Mansonones and coumarins were isolated from the heartwoods of M. gagei and were elucidated as mansorins A, B, C, mansonones C, E, G and H. Eight compounds were isolated from M. fruticosum flower, including 1-hexacosanol, 5-hydroxy-7-methoxyflavone, β-sitosterol, benzoic acid, 5,7-dihydroxyflavone, melodorinol, melodorinones A and B. Among the isolated compounds, mansonone C displayed the highest antifungal activity against P. parasitica with IC50 3.2 µg·mL-1. For the inhibition of spore germination, ACA displayed the highest activity against spore germination of F. oxysporum at 100 µg·mL-1, followed by mansonones E and G. ACA displayed in vivo complete inhibition against disease lesion caused by P. parasitica on pineapple leave, while it slightly inhibited the heart rot disease in pineapple suckers. Nevertheless, there was no synergistic effect observed on the combination of ACA, mansonone E and melodorinol.