Antifungal activity against Colletotrichum spp. of curcuminoids isolated from Curcuma longa L. rhizomes

Methanol extract of the rhizomes of turmeric, Curcuma longa L., effectively controlled the development of red pepper anthracnose caused by Colletotrichum coccodes. In addition three antifungal substances were identified from the methanol extract of C. longa rhizomes as curcumin, demethoxycurcumin, and bisdemethoxycurcumin using mass and H-1-NMR spectral analyses. The curcuminoids in a range 0.4-100 mu g/ml effectively inhibited the mycelial growth of three red pepper anthracnose pathogens, C. coccodes, C. gloeosporioides, and C. acutatum. The three curcuminoids inhibited mycelial growth of C. coccodes and C. gloeosporioides to an extent similar to the synthetic fungicide dithianon did, but the synthetic agent was a little more effective against C. acutatum. The curcuminoids also effectively inhibited spore germination of C. coccodes, and bisdemethoxycurcumin was the most active. Among the three curcuminoids, only demethoxycurcumin was effective in a greenhouse test in suppressing red pepper anthracnose caused by C. coccodes.