The Antifungal Activity of Gallic Acid and Its Derivatives against Alternaria solani, the Causal Agent of Tomato Early Blight

Asmaa El-Nagar,Yasser Nehela,Naglaa A Taha,Abdelnaser A Elzaawely

doi:10.3390/agronomy10091402

Abstract

Tomato (Solanum lycopersicum L.) is among the most important vegetable crops worldwide. Early blight disease, caused by Alternaria solani, is a destructive foliar disease of tomato and other Solanaceae species. Herein, we investigated the in vitro antifungal properties of gallic acid and two of its derivatives (syringic and pyrogallic acids) against A. solani during 2019 and 2020 seasons. The physiological and biochemical effects of these compounds on infected tomato plants were also investigated using the whole plant bioassay. The in vitro investigation showed that all tested compounds showed fungistatic action and inhibited the mycelial radial growth of A. solani in a dose-dependent manner. In two separate pot-experiments, those compounds efficiently suppressed the development of the disease symptoms and area under disease progress curve (AUDPC), without any phytotoxic effects on the treated tomato plants. Additionally, all tested compounds positively enhanced the biochemical traits of treated plants including the chlorophyll content, the total soluble phenolics, the total soluble flavonoids, and the enzymatic activities of catalase, peroxidase, and polyphenol oxidase during 2019 and 2020 seasons. Moreover, the treatment with gallic acid and its derivatives significantly increased all yield components of A. solani-infected tomato plants such as the total number of flowers and fruits, and the fruit yield for each tomato plant in both experiments. Considering the fungitoxicity of phenolic acids against A. solani with no phytotoxicity on treated tomato plants, we believe that gallic acid and its derivatives might be a sustainable eco-friendly control strategy to reduce the usage of chemical fungicides partially or entirely against A. solani particularly, and fungal diseases in general.

Highlights

Tomato (Solanum lycopersicum L.) is one of the most important vegetable crops worldwide and the second most consumed vegetable crop after potato
303.69 ± 42.85 in 2019 and 2020 seasons, respectively). These findings indicate that the exogenous treatment with gallic acid and its derivatives alleviates the harmful effects of A. solani on tomato leaves and suppresses the development of the disease symptoms
These findings indicate that the exogenous treatment with gallic acid and its derivatives alleviates the harmful effects of A. solani on the leaf surface of tomato plants and suppresses the development of the disease symptoms

Summary

Introduction

Tomato (Solanum lycopersicum L.) is one of the most important vegetable crops worldwide and the second most consumed vegetable crop after potato. Tomato is considered a tropical plant, it grows in temperate climates in almost every country worldwide under a broad range of production systems. According to the compendium of tomato diseases and pests, tomato plants might be threatened by more than 60 phytopathogens, including viruses, bacteria, fungi, and oomycetes, which cause serious diseases and considerable yield losses [4]. Among these diseases, early blight disease is considered one of the most destructive foliar diseases of tomato plants and other plant species in the family Solanaceae, including potato, eggplant, and pepper [4,5,6,7]. A. solani reproduces asexually by multicellular conidia which can form visible necrotic lesions 2–3 days postinfection and reproduce new conidia 3–5 days later [6,9]

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