Tomato, Solanum lycopersicum is one of the most important vegetable crops consumed in Algeria. Tomato crops are often infected by Alternaria alternata, which causes early blight disease. Chemical pesticides are intensively used to protect this plant, which lead to environmental pollution that might endanger animal and human health. The main objective of this study is to select potential biocontrol agents from arid soil as an alternative to chemical products. The phytopathogenic fungus which was isolated from infested tomato leaves, stems and fruits cultured in Constantine-Algeria, was identified as Alternaria cf. alternata. Thirty five bacteria isolates were obtained from arid soil in the south of Algeria. Three of the isolates inhibited the growth of A. alternata. However, the most potent isolate, E1B3 reached a 75% inhibition rate. The molecular identification of this isolate showed that it was closely related to Bacillus mojavensis (KC977492). This strain does not produce chitinase, but does produce lipase, protease and lipopeptides. The interaction between A. alternata and B. mojavensis was investigated for the first time in this work by flow cytometric analysis. In conclusion, B. mojavensis strain was antagonistic to A. alternata which could possibly be exploited as a biopesticide in tomato crops management.Keywords: Tomato, Bacillus mojavensis, early blight, Alternaria alternata, flow cytometr
