One of the tomato’s acutely devastating diseases is Alternaria leaf spot, lowering worldwide tomato production. In this study, one fungal isolate was isolated from tomatoes and was assigned to Alternaria alternata TAA-05 upon morphological and molecular analysis of the ITS region and 18SrRNA, endoPG, Alt a1, and gapdh genes. Also, Urtica dioica and Dodonaea viscosa methanol leaf extracts (MLEs) were utilized as antifungal agents in vitro and compared to Ridomil, a reference chemical fungicide. The in vitro antifungal activity results revealed that Ridomil (2000 µg/mL) showed the highest fungal growth inhibition (FGI) against A. alternata (96.29%). Moderate activity was found against A. alternata by D. viscosa and U. dioica MLEs (2000 µg/mL), with an FGI value of 56.67 and 54.81%, respectively. The abundance of flavonoid and phenolic components were identified by HPLC analysis in the two plant extracts. The flavonoid compounds, including hesperidin, quercetin, and rutin were identified using HPLC in D. viscosa MLE with concentrations of 11.56, 10.04, and 5.14 µg/mL of extract and in U. dioica MLE with concentrations of 12.45, 9.21, and 5.23 µg/mL, respectively. α-Tocopherol and syringic acid, were also identified in D. viscosa MLE with concentrations of 26.13 and 13.69 µg/mL, and in U. dioica MLE, with values of 21.12 and 18.33 µg/mL, respectively. Finally, the bioactivity of plant extracts suggests that they play a crucial role as antifungal agents against A. alternata. Some phenolic chemicals, including coumaric acid, caffeic acid, ferulic acid, and α-tocopherol, have shown that they may be utilized as environmentally friendly fungicidal compounds.
