Extracts and metabolites derived from the leaves of Cassia alata L. exhibit in vitro and in vivo antimicrobial activities against fungal and bacterial plant pathogens

•Bioassay-guided fractionation led to the identification of antimicrobial constituents from Cassia alata.•Methanol and ethyl acetate-soluble extracts of C. alata are rich in aloe-emodin, rhein and aloe-emodin-8-O-β-D-glucoside.•Ethyl acetate-soluble extract strongly suppressed four plant diseases in vivo.•In vitro and in vivo potent suppression of Phytophthora species by the ethyl acetate-soluble extract and rhein was observed.•Rhein highly inhibited Acidovorax avenae subsp. cattlvae with a half maximal inhibitory concentration (IC50) of 2.5 μg/mL.