Antifungal Activity of Alkaloids from Murraya koenigii (Linn.) Spreng against Alternaria brassicae (Berk.) Sacc.

Among eleven botanical methanolic crude extracts tested through spore germination inhibition test against Alternaria brassicae, the fraction of Murraya koenigii (Linn.) Spreng was most effective with a minimum inhibitory concentration of 216 μg/ml. Methanolic (MeOH) extract of Murraya koenigii exhibited antifungal activity with R_f value 0.83 of zone of inhibition against A. brassicae by direct bioautography. The MeOH fraction was further fractionated into nine column chromatography sub-fractions (CSFs) (I-IX) to identify the antifungal bioactive compounds. CSFs II and III exhibited strong inhibitory effect on conidial germination of A. brassicae with the lowest MIC values of 25 and 23.25 μg/ml, whereas CSF IV, V, VI, VII and VIII were effective at 10% dilution (45.5–59 μg/ml). These nine CSFs were further used to investigate their effect on lesion development of Alternaria blight on detached leaves of Indian mustard at 1.25%, 2.5%, 5% and 10% dilutions, respectively. Only CSF VIII at concentration of 59 μg/ml (10% dilution) completely inhibited lesion development of A. brassicae, whereas control (treatment with water instead of CSFs) showed distinct leaf lesion of A. brassicae. Diagnosis of methanolic leaf extract of Murraya koenigii with Dragendorff reagent indicated that the active compounds comprised of alkaloids.