Efficacy of Thai plant extracts against grain discoloration disease in rice (Oryza sativa L.)

Abstract

The antifungal effect was examined of ethanolic crude extracts of four plants on the mycelial growth and conidial germination of Curvularia lunata and Fusarium sacchari, which are the principal causal agents of grain discoloration disease in rice. The four plants studied were: Cassia spectabilis (leaves and flowers); Syzygium aromaticum (buds); Alpinia galanga; and Curcuma zedoaria (aerial part and rhizome). The extract of S. aromaticum showed 100% inhibition on the mycelial growth and conidial germination of both C. lunata and F. sacchari at all concentrations. The extract of A. galanga rhizome at 10,000 parts per million (ppm) also completely inhibited both mycelial growth and conidial germination of F. sacchari. The extracts of leaves and flowers from C. spectabilis displayed 100% inhibition against conidial germination at both 5,000 ppm and 10,000 ppm. The ethanolic extracts of S. aromaticum and A. galanga rhizome were separated based on column chromatography and used for bioassay. The active compounds were characterized as eugenol from S. aromaticum and 1´-acetoxychavical acetate (ACA) from A. galanga. The minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of the active compounds were determined using 96-well microplates against the fungal pathogens. The ACA fraction showed the highest antifungal activity against C. lunata (MIC = 23.43 ppm and MFC = 23.43 ppm) and F. sacchari (MIC = 46.87 ppm and MFC = 93.75 ppm). The results indicated the tested plant extracts had the potential to be used as eco-friendly pesticides to control grain dislocation disease in rice.