Urtica dioica and Dodonaea viscosa leaf extracts as eco-friendly bioagents against Alternaria alternata isolate TAA-05 from tomato plant

Abstract

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.

Figure 1

Alternaria alternata growth on a Petri dish (A) and conidiophore bearing the septated conidium was photographed under a light microscope 40x (B).

Figure 2

Constructed phylogenetic tree based on 10 most parsimonious ITS sequences. The Egyptian fungal isolate is Alternaria alternata TAA-05 (OL673807).

Figure 3

Constructed phylogenetic tree based on 16 most parsimonious 18SrRNA sequences. The Egyptian fungal isolate is Alternaria alternata TAA-05 (OL674053).

Figure 4

Visual observation of the antifungal activity of U. dioica extract (A), D. viscosa extract (B), and Ridomil fungicide (C) against the growth of A. alternata isolate.

Figure 5

HPLC chromatograms of flavonoid compounds identified in the methanol leaf extracts of U. dioica (A) and D. viscosa (B).

Figure 6

HPLC chromatograms of phenolic compounds identified in the methanolic leaf extracts of U. dioica (A) and D. viscosa (B).

Figure 7

Antifungal activity of Urtica dioica and Dodonaea viscosa most abundant compounds and mixtures. A = Control, B = Positive control (Ridomil), C = Caffeic acid, D = Ferulic acid, E = α-Tocopherol, F = Ferulic acid + caffeic acid, G = Ferulic acid + coumaric acid, H = Ferulic acid + α-tocopherol, I = Caffeic acid + coumaric acid, J = Caffeic acid + α-tocopherol, K = Coumaric acid + α-tocopherol, L = Coumaric acid, M = Total mixture.