The discovery of plant secondary compounds with antimicrobial activity is very promising. Turmeric, Curcuma longa, has compounds in its rhizomes with fungicidal activity. The objective of this study was to evaluate the in vitro fungitoxic activity of turmeric extracts and curcumin against Alternaria solani. Four different concentrations (0, 1, 5, 10 and 20%) of aqueous extracts of turmeric rhizomes (sterilized by autoclave) and four curcumin solutions (0, 50, 100, 200 and 400 mg/L) were incorporated into potato dextrose agar medium in order to evaluate fungal mycelial growth and sporulation. To evaluate the effect of using an autoclave, 10% and 15% turmeric extracts were sterilized by filtration. The effects of autoclaved and non-autoclaved turmeric extracts and curcumin on in vitro spore germination were tested. The concentrations of 10 and 15% of non-autoclaved turmeric extracts inhibited the mycelial growth by 38.2% and 23.2% respectively and the fungal sporulation by 71.7% and 87% respectively. When turmeric extracts were autoclaved, neither mycelial growth nor spore germination was inhibited and the effect on sporulation was reduced, suggesting the presence of thermolabile antimicrobial compounds. The non-autoclaved 5% extract inhibited spore germination by up to 15%. At the highest concentration, the curcumin solution inhibited mycelial growth by 29.5%. Neither in vitro sporulation nor spore germination was affected by curcumin. These results show the fungitoxic potential of turmeric and curcumin against A. solani.
medicinal plant; turmeric; plant extract; tomato early blight; alternative plant disease control
