Evaluation de l’activité antifongique de l’extrait aqueux de l’Atriplex halimusvis-à-vis de l’Alternaria solani agent del’alternariose sur tomate(Lycopersicum esculentum)

Abstract

Alternaria blight, or Alternaria leaf spot, is a common foliar disease of potatoes that also affects tomatoes, eggplants, and other related plants. If not treated promptly and effectively, it can reduce crop yields. This study aims to evaluate the antifungal activity of extracts from a medicinal plant, Atriplex halimus, against the phytopathogenic fungus Alternaria solani, responsible for Alternaria leaf spot in several crops, including tomatoes. Through in vitro assays, the study seeks to measure the inhibitory effect of this extract on mycelial growth and sporulation of the pathogen in order to propose a natural alternative to conventional chemical treatments. Based on the results obtained, it is observed that Alternaria solani strains develop as greenish, shaved colonies with a black underside and a velvety or cottony appearance, often with concentric rings. Microscopic observation reveals a septate and branched mycelium, ranging in color from pale brown to dark brown. The conidiophores are brown, septate, simple, or sometimes branched. The conidia are large, brown, obclavate (club-shaped), with several transverse and a few longitudinal septa. Under different concentrations of the aqueous extract of Atriplex halimus on the Alternaria solani isolate, there was a marked decrease in the diameter of the treated colonies compared to the control. A progressive decrease in growth was observed at concentrations of 6.25%, 12.5%, 25%, and 50%, and the mycelial growth rate of Alternaria solani decreased with increasing concentrations of the aqueous extract of Atriplex halimus. High extract concentrations significantly stimulated the growth rate. At a dose of 12.5%, a rate of 0.51 cm/day was recorded, and then it dropped to 0.05 cm/day at a dose of 25%. Above 50%, no growth was observed, indicating complete inhibition of fungal development. The highest inhibition rate was recorded at a concentration of 3.12%, with a sporulation rate of 72.46%. The sporulation rate was recorded at concentrations of 3.12% and 6.15%, or at concentrations of 12.12% and 19.16%. The highest inhibition rate was recorded at a concentration of 100%, with a sporulation rate of 75.25%.