Antibacterial activity of moroccan plants extracts against Clavibacter michiganensis subsp . michiganensis, the causal agent of tomatoes' bacterial canker

Abstract

In search for alternative ways of tomatoes’ bacterial canker control, we screened here forty medicinal and aromatic plants (MAP) sampled from 15 families, currently used in southern Moroccan traditional medicine, for their activity against Clavibacter michiganensis subsp . michiganensis the causal agent of this disease. The antibacterial efficacy of powders of these plants was determined in vitro using the agar plate’s methods. Results obtained show that all the forty plants tested inhibited the bacterial growth of this pathogen with inhibition zone diameter ranging from 5 to 50 mm. Determination of the minimal inhibitory concentrations (MIC) and the minimal bactericidal concentrations (MBC) of the most effective plants indicates that there plants gender Rubus, Anvillea and Pistacia have the lower MIC which is equal to 3,125 mg ml -1 . The other plants ( Lavandula coronopifolia, Lavandula stoechas, Rosa canina, Cistus monspliensis and Cistus crispus ) had a MIC equal to 6.25 mg ml -1 . The MBC for different plants tested are between 6.25 mg ml -1 , case of Rubus ulmifolius and 25 mg ml -1 . The germination percentage of seeds treated with the most efficient three plants extracts was significantly higher than the untreated. Seeds treated with the extract of L. coronopifolia gave the higher germination rate (98%). The rate germination is 84 to 88% respectively for Cistus monspeliensis and Rubus ulmifolius . In other hand population size of the bacterium in the seeds’ surface was significantly reduced compared to the controls for the three treatments, when tomato seeds were artificially inoculated with the pathogen before being treated with the plants extracts (aqueous extracts).