In vitro Development of Two Alternaria solani Strains, Causal Agent of Alternariose in Tomato (Lycopersicon esculentum) under the Influence of Thevetia peruviana Seeds Extracts

Alternaria solani is a fungus that causes yield losses of up to 80 % in tomato production in field. Synthetic fungicides are the most widely used for its controbl, but have harmful consequences. The objective of this work was to test in vitro the antifungal potential of Thevetia peruviana seed extracts against two A. solani isolates. Aqueous, methanol, ethyl acetate and acetone extracts, at concentrations 12.5, 25, 50 and 100 µL/mL were used. Two synthetic fungicides Maneb (5.33 µg/mL) and Dimethomorph + Clorothalonil (3.75 µg/mL) and control (0 µL/mL) were also tested on two A. solani isolates (Mbal and Foum). The investigation was repeated three times. Phytochemical screening, mycelial growth, spore germination and minimum inhibitory concentrations (MIC50 and MIC90) were determined. The results showed that T. peruviana extracts are rich in many families of bioactive compounds such as alkaloids, phenolic compounds and sugars. All extracts tested show high inhibition of mycelial growth (100%) and spore germination (100%) of the two strains at highest concentration (100 µL/mL). Acetone extract at a concentration of 50 µL/mL inhibited mycelial growth by 88.45 and 86.55% and spore germination by 88.33 and 80.33%, respectively for the Mbal and Foum isolates. The lowest MIC50 (16.63 µL/mL) and MIC90 (54.6 µL/mL) were obtained with the acetone extract on the Mbal isolate while the highest MIC50 (27.5 µL/mL) and MIC90 (61.7 µL/mL) were observed with ethyl acetate on the Foum isolate These extracts can therefore be used in the biological control against Alternariose in tomato.