Control of Tomato Early Blight (Alternaria solani) Disease by Aqueous Extract of Thyme (Thymus vulgaris)

Document Type : Research Article

Authors

• Ali Gholamzadeh-Bazarbash ¹
• Sahar Qoli Toloui ¹
• Tohid Alllahverdipour ²
• mehrdad salehzadeh ³

¹ Department of Plant Protection, College of Agriculture, Afaq Institute of Higher Education, Urmia, Iran

² Department of Plant Protection, College Institute, Urof Agriculture Afagh Higher Education mia, Iran

³ Plant Virology Research Center, School of Agriculture, Shiraz University, Shiraz, Iran.

10.22067/jpp.2025.87475.1183

Abstract

Introduction
Tomato (Solanum lycopersicum) is the second most valuable agricultural product after potatoes. Early blight, caused by Alternaria solani, is a major disease affecting tomatoes, damaging stems, leaves, and fruits. This disease significantly reduces photosynthesis and can lead to leaf drop in severe cases across tomato-growing regions in Iran. Common control methods often involve chemical pesticides, but their excessive use can result in environmental pollution, pathogen resistance, and the emergence of dangerous strains, exacerbating the damage. As a safer alternative, researchers have increasingly focused on using natural compounds, or phytometabolites, for pest and pathogen management. Plant biocides offer numerous advantages, including rapid decomposition, specific toxicity, reduced bioaccumulation, and minimal harm to beneficial insects. This study aims to evaluate the effectiveness of thyme extract in managing tomato spot disease as a substitute for chemical pesticides, alongside an assessment of morphological and physiological characteristics in infected versus healthy plants.
 
Materials and Methods
Five fungal isolates were collected from tomato fields in various locations of West Azarbaijan province. Extraction and isolation of A. solani followed the Rigotti method (2003), while DNA extraction and PCR were conducted using Ji Cho's method (2016), with the amplified fragments subsequently sequenced. A phylogenetic tree was created using Mega 8 software, positioning the Iranian isolate alongside Asian A. solani isolates. Thyme extract's effect on fungal colony growth was tested in the lab, and pathogenicity was assessed on tomato variety 4129. Morphological traits, including plant and root length and biomass, along with physiological traits such as chlorophyll content and the expression of defense genes (CAT, APX, POD), as well as phenol and flavonoid levels were measured for UrmiaB isolate, as the most virulent among the collected isolates.
 
Results and Discussion
All concentrations of thyme extract tested in this research exhibited significant inhibitory and antifungal effects at both 1% and 5% probability levels compared to the controls. Additionally, thyme extract showed moderate to high antifungal activity against A. solani, both in laboratory and greenhouse settings. In laboratory trials, thyme concentrations of 50, 100, and 150 mg mL^-1 markedly reduced fungal growth, particularly at higher concentrations (100 and 150 mg mL^-1), which also corresponded with a decrease in pathogenicity affecting tomato fruits of cultivar 4129. Morphological and physiological assessments indicated that thyme extract improved traits in tomato variety 4129, including root and shoot lengths, biomass, chlorophyll content, and the expression of defense-related enzymes (CAT, APX, POD), as well as phenolic and flavonoid levels under greenhouse conditions. These findings demonstrate that thyme extract effectively mitigates early blight disease in tomatoes by inhibiting fungal growth.
 
Conclusion
The results indicated that thyme extract effectively reduced the activity of the pathogen responsible for tomato early blight in both laboratory and greenhouse conditions. Its antifungal properties make thyme extract a promising candidate for commercialization in agricultural pest management, particularly when used in combination with other compounds.
 

Keywords

• Antifungal properties
• Early blight
• Morpho-physiological traits
• Plant metabolite

Main Subjects

• قارچ شناسی

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©2024 The author(s). This is an open access article distributed under Creative Commons Attribution 4.0 International License (CC BY 4.0), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source.

https://doi.org/10.22067/JPP.2025.87475.1183

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