In vitro evaluation of some Egyptian plants against the rot bacteria and spider mite and isolation the active constituent(s) from Myrtus communis leaves

The present study investigated activity of 4 different extracts of 25 local plant species belonging to 17 families against two phytopathogenic bacteria, Erwinia carotovora and Ralstonia solanacearum the pathogens of soft rot and brown rot diseases of many important cultivated plants together with phytophagous mite, twospotted spider mite, Tetranychus urticae which feed on numerous food and fiber crops causing serious damage and crop loss worldwide. The biological evaluation results indicated that Myrtus communis was the most potent to combat these pests. Bioactivity-guided separation of the bioactive methanol extract of the dried leaves of Myrtus communis resulted in the isolation of a chromatographically pure compound. Based on spectroscopic methods (¹H, ¹³C-NMR and MS) as well as chemical methods (detection tests and acidic hydrolysis). The active compound which isolated for the first time from this plant was characterized as 3-methoxy myricetin 7-O- α-L-rhamnopyranoside. This compound exerted a bactericidal activity against both Erwinia carotovora and Ralstonia solanacearum with MLC values of 200 and 100 μg.ml^-¹ respectively, along with an acaricidal activity against the tested mite with LC50 value of 67 mg/l.