Antimicrobial flavonoids from the twigs of Populus nigra × Populus deltoides

Abstract

A bioassay-guided fractionation of the ethyl acetate extract from the twigs of the hybrid poplar ‘Neva’, Populus nigra L. × Populus deltoides Marsh, led to the isolation of three flavonoids, which were identified by means of spectrometric and physicochemical analysis as 5-hydroxy-7-methoxy-flavone (1), 5,7-dihydoxy-flavone (2) and 5,7-dihydroxy-flavonol (3). These compounds were further screened for their antimicrobial activity against plant pathogens, including three bacteria (Pseudomonas lachrymans, Ralstonia solanacearum and Xanthomonas vesicatoria) and one fungus (Magnaporthe oryzae). Compounds 2 and 3 showed significant antibacterial activity, with minimum inhibitory concentrations (MICs) ranging from 15 to 25 µg mL⁻¹, and median inhibitory concentrations (IC₅₀ values) from 4 to 18 µg mL⁻¹. The results obtained provide promising baseline information for the potential use of the extract and flavonoids from this plant as antimicrobial agents to help control plant diseases.

Keywords:

• antimicrobial activity
• flavonoids
• hybrid poplar
• Populus
• Salicaceae

Acknowledgements

This work was co-financed by grants from the Hi-Tech Research and Development Program of China (2006AA10A209 and 2006AA10Z423) and the National Key Technology R&D Program of China (2007BAD89B01). The authors are grateful to Prof. Yuying Xiang of the Institute of Forestry, Chinese Academy of Forestry for plant species identification.