Assessment of antibacterial properties of medicinal plants having bacterial leaf endophytes against plant pathogenic Xanthomonads

Abstract

Assessment of antibacterial property in plants by direct testing of aqueous plant extract or solvent extracted plant extracts on test pathogen is a time consuming process and therefore the preliminary assessment technique to confirm antibacterial property in unknown plant is needed. Presence or absence of bacterial endophytes in the leaves of 56 medicinal plants was considered for the assessment of antibacterial compound in these medicinal plants. Absence of leaf endophytic bacteria in 29 medicinal plants was considered as a basis of presence for antibacterial compound in these plants. This was confirmed by inhibition of growth of the test bacterium, in the sterilized aqueous extract of three medicinal plants. The medicinal plant showing bacterial inhibition zone was further confirmed for antibacterial compound by formation of inhibition zone by aqueous extract, ethanol extract and methanol extract on test bacterium by paper disc method. Medicinal plants which did not have bacterial endophytes, possessed antibacterial property in their aqueous leaf extract against Xanthomonads. Out of 29 medicinal plants which did not have leaf endophytic bacteria, 3 plants viz., Simarouba glauca, Terminalia chebula and Bixa orellana Linn were found to possess antibacterial property against Xanthomonas sp. The presences of antibacterial compound in these plants were up to 500 µg/ml of aqueous leaf extract. Thus, the medicinal plants which did not have endophytic bacteria in their leaves can be considered for the presence of antibacterial compound.