Insecticidal and Antifungal Activities of Crude Extracts and Pure Compounds from Rhizomes of Curcuma longa L. (Zingiberaceae)

The insecticidal and antifungal activities of Curcuma longa L. rhizome extracts and two isolated compounds, namely, ar-turmerone and curcumin, were evaluated. Rhizomes of C. longa were extracted with n-hexane, methylene chloride, methanol and water, successively. Hexane, methylene chloride, and methanol extracts exhibited remarkable insecticidal activity against the larvae of Culex pipiens. The LC50 values were 5.28, 5.82, and 6.44 mg L-1, respectively, after 48 h. In contrary, the extracts exhibited weak toxic effect on the third instar larvae of Spodoptera littoralis. The LC50 values of water, methylene chloride, and hexane extracts were 495.9, 565.7 and 709.7 mg L-1, respectively after 48 hours. On the other hand, the extracts showed variable antifungal activity against plant pathogenic fungi, Fusarium oxysporum, Pythium debaryanum, Phytophthora infestans, Fusarium solani and Alternaria alternata. Methanol extract had the highest antifungal activity among the tested extracts with EC50 values of 159.8, 242.7, and 322.2 mg L-1 on P. infestans, F. solani and A. alternata, respectively. Two compounds, namely, ar-turmerone and curcumin were isolated from methylene chloride/methanol (1:1) extract of C. longa rhizomes and their chemical structures were identified by using spectroscopic analysis. Ar-Turmerone had moderate toxicity against C. pipiens larvae. The LC50 values were 158.5 and 117.6 mg L-1 after 24 and 48 hours, respectively. In addition, arturmerone showed moderate antifungal activity against P. infestans (EC50= 588.9 mg L-1) and weak activity against F. solani (EC50= 820.6 mg L-1). Curcumin caused 51.1 and 54.32% growth inhibition of F. oxysporum and P. infestans at 250 mg L-1, respectively.