Antifungal activity ofAgave americanaleaf extract againstAlternaria brassicae, causal agent ofAlternariablight of Indian mustard (Brassica juncea)

Leaf extract of Agave americana was evaluated for antifungal activity against Alternaria brassicae, the causal agent of Alternaria blight of Indian mustard [Brassica juncea (L.) Czern. & Coss]. Methanolic leaf extract (crude extract) of A. americana showed antifungal activity against A. brassicae. The green mass obtained by vacuum drying of the crude extract was used for further sequential fractionation using ethyl acetate, n-butanol and methanol. Among the three fractions, the methanolic fraction showed the strongest antifungal activity by its inhibition of conidial germination of A. brassicae. The methanolic fraction of A. americana leaves was fractionated further using open column liquid chromatography into six sub-fractions (I – VI). Among the six sub-fractions tested, sub-fraction II showed a strong inhibitory effect on conidial germination of A. brassicae and thereby inhibited lesion development of Alternaria blight of Indian mustard at a concentration of 40 µg/ml or higher. Qualitative separation of molecules present in sub-fraction II by thin layer chromatography followed by diagnosis with Libermann – Burchard reagent indicated that sub-fraction II contained a mixture of saponins. The potential of using A. americana for the management of fungal pathogens of crop plants is discussed.