Common bacterial blight (CBB) caused by Xanthomonas axonopodis pv. phaseoli (Xap) have been recorded as one of the most important seed-borne destructive diseases on beans. Chemical compounds which are incessantly used on beans to manage CBB disease cause serious damage to natural ecosystems and sometimes they show frequent failure for controlling CBB. These consequences are attributed to the use of by-products from aromatic and medicinal plants. The active ingredient of these plants can inhibit the biofilm formation of different bacterial pathogens. In this study, the effect of aromatic and medicinal plant extracts on biofilm formation of X. axonopodis pv. phaseoli were investigated. The result showed that all plant extracts significantly reduced the biofilm formation of Xap as compared to the control treatment. Twelve of the 14 plant extracts inhibited Xap biofilm formation by >50%. The extract of Clove (Syzygium aromaticum (L.), Coriander (Coriandrum sativum L.), Thyme (Thymus vulgaris L.), Mustard (Brassica nigra (L.), Garden Rue (Ruta chalepensis L.), Garden cress (Lepidium sativum L.), Black cumin (Nigella sativa L.) and Black pepper (Piper nigrum L.) inhibited Xap biofilm formation by 90.85, 87.67, 84.94, 81.10, 79.93, 77.33, 75.17 and 72.02%, respectively. This clearly indicated that crude extracts of S. aromaticum, C. sativum, T. vulgaris, B. nigra, R. chalepensis, L. sativum, N. sativa, and P. nigrum had the greatest effect on biofilm formation and to be a potential candidate as anti-biofilm agents in preventing common bacterial disease of beans caused by Xap.

Keywords: Anti-biofilm activity, Plant extracts, Xanthomonas axonopodis pv. phaseoli