Efficacy of ethanolic extracts of galangal (Alpinia galanga) in inhibiting the mycelial growth of Fusarium sacchari and Curvularia lunata and their phytotoxicity on pak choi (Brassica rapa var. chinensis)

The extracts of galangal (Alpinia galanga) have a rich background as antimicrobial agents. This study therefore determined the efficacy of galangal rhizome ethanolic extract (CE) in controlling Curvularia lunata and Fusarium sacchari and the phytotoxicity on seed germination and seedling growth of pak choi (Brassica rapa var. chinensis). The extracts were obtained by maceration with different concentrations of ethanol, such as CE 40, 50, 60, 70, 80 and 95%. The antifungal activity was tested at a dose 10% of CE in solution. CE 60, 80 and 95% significantly inhibited the mycelial growth of F. sacchari with 85.12 to 90.83% inhibition. CE 60% was the strongest inhibitor of C. lunata displaying 82.12% inhibition. Seedling vigor index (SVI) was determined to assess the effect of the extracts on the seedling growth. Fresh weight of the seedling of pak choi was also determined. Seedlings treated with CE 40% showed the highest SVI (significant p≤0.05), compared with CE 50 and 60% while CE 80% registered the weakest vigor. CE 40, 50 and 60%, respectively, promoted root growth significantly but had slight inhibition (<30%) on shoot growth. Overall, no significant effect on seedling growth was observed when compared to the control. Therefore, the CE has potential to suppress F. sacchari and C. lunata, two major causal agents of plant diseases. Nevertheless, this CE has a minimal effect on seedling growth but this can be mitigated if appropriate extraction solvent and dose is applied in the field.