Screening of agricultural field bacteria and highlighting of their antagonistic effects on post-harvest disease fungi

In this study, the isolation of 374 antagonist bacterial strains was carried out on two agricultural biotopes in which 245 strains were isolated from the soil, 69 from the leaves and finally 60 from the roots of both plants. The screening of the antagonism of these 374 isolates was performed against three phytopathogenic fungi, Fusarium oxysporum, Botrytis cinerea and Alternaria alternata, finding that 24 isolates had antagonistic activity with a mycelial growth inhibition rate equal or higher than 37%. These 24 bacterial isolates were identified on the basis of morphological, physiological and biochemical characters. The comparison with the dual culture technique allowed 6 bacterial isolates (Fr43, F31, Fr52, F101, B6 and B29) to be retained with areas of significant inhibition against F. oxysporum, B. cinerea and reached a value between 27 and 52 mm. However, these isolates showed significant inhibitory activity against mycelial growth (varies between 25.88% and 67.05%) and sporulation (varies between 68.74 and 100%) of B. cinerea and F. oxysporum by their supernatant. Concerning the growth promotion, the Fr43 strain was the most active with a GPE % between 25.31 and 60, 71% according to the part of the plant. This isolate was also shown to significantly reduction of the incidence disease to 15.3%, which corresponds to a significant efficacy of biological control that can reach 79.92% against F. oxysporum. On the contrary, the isolate F101 exhibited the lowest value of the effectiveness of biological control versus control which can reach only 37.46%.