Hydroxylated Cinnamates Enhance Tomato Resilience to Alternaria alternata, the Causal Agent of Early Blight Disease, and Stimulate Growth and Yield Traits.

The important vegetable crop, tomato, is challenged with numerous abiotic and biotic stressors, particularly the newly emerged fungicide-resistant strains of phytopathogenic fungi such as Alternaria alternata, the causal agent of early blight disease. The current study investigated the potential antifungal activity of four cinnamate derivatives including cinnamic acid, ρ-coumaric acid, caffeic acid, and ferulic acid against A. alternata. Our in vitro findings showed that all tested compounds exhibited dose-dependent fungistatic action against A. alternata when their concentrations were increased from 0.1, 0.3, 0.5, and 0.7, to 0.9 mM, respectively. The high concentration of ferulic acid (0.9 mM) completely inhibited the radial mycelial growth of A. alternata and it was comparable to the positive control (difenoconazole fungicide). Additionally, under greenhouse conditions, foliar application of the four tested cinnamates significantly reduced the severity of early blight disease without any phytotoxicity on treated tomato plants. Moreover, it significantly improved the growth traits (plant height, total leaf area, number of leaves per plant, and shoot fresh weight), total chlorophyll, and yield components (number of flowers per plant, number of fruits per plant, and fruit yield) of treated A. alternata-infected plants. Collectively, our findings suggest that cinnamate derivatives could be good candidates as eco-friendly alternatives to reduce the use of chemical fungicides against A. alternata.

Benzimidazole Derivatives Suppress Fusarium Wilt Disease via Interaction with ERG6 of Fusarium equiseti and Activation of the Antioxidant Defense System of Pepper Plants.

Sweet pepper (Capsicum annuum L.), also known as bell pepper, is one of the most widely grown vegetable crops worldwide. It is attacked by numerous phytopathogenic fungi, such as Fusarium equiseti, the causal agent of Fusarium wilt disease. In the current study, we proposed two benzimidazole derivatives, including 2-(2-hydroxyphenyl)-1-H benzimidazole (HPBI) and its aluminum complex (Al-HPBI complex), as potential control alternatives to F. equiseti. Our findings showed that both compounds demonstrated dose-dependent antifungal activity against F. equiseti in vitro and significantly suppressed disease development in pepper plants under greenhouse conditions. According to in silico analysis, the F. equiseti genome possesses a predicted Sterol 24-C-methyltransferase (FeEGR6) protein that shares a high degree of homology with EGR6 from F. oxysporum (FoEGR6). It is worth mentioning that molecular docking analysis confirmed that both compounds can interact with FeEGR6 from F. equiseti as well as FoEGR6 from F. oxysporum. Moreover, root application of HPBI and its aluminum complex significantly enhanced the enzymatic activities of guaiacol-dependent peroxidases (POX), polyphenol oxidase (PPO), and upregulated four antioxidant-related enzymes, including superoxide dismutase [Cu-Zn] (CaSOD-Cu), L-ascorbate peroxidase 1, cytosolic (CaAPX), glutathione reductase, chloroplastic (CaGR), and monodehydroascorbate reductase (CaMDHAR). Additionally, both benzimidazole derivatives induced the accumulation of total soluble phenolics and total soluble flavonoids. Collectively, these findings suggest that the application of HPBI and Al-HPBI complex induce both enzymatic and nonenzymatic antioxidant defense machinery.

Metal Complexation of Bis-Chalcone Derivatives Enhances Their Efficacy against Fusarium Wilt Disease, Caused by Fusarium equiseti, via Induction of Antioxidant Defense Machinery.

Sweet pepper (Capsicum annuum L.) is one of the most widely produced vegetable plants in the world. Fusarium wilt of pepper is one of the most dangerous soil-borne fungal diseases worldwide. Herein, we investigated the antifungal activities and the potential application of two chalcone derivatives against the phytopathogenic fungus, Fusarium equiseti, the causal agent of Fusarium wilt disease in vitro and in vivo. The tested compounds included 3-(4-dimethyl amino-phenyl)-1-{6-[3-(4 dimethyl amino-phenyl)-a cryloyl]-pyridin-2-yl}-propanone (DMAPAPP) and its metal complex with ruthenium III (Ru-DMAPAPP). Both compounds had potent fungistatic activity against F. equiseti and considerably decreased disease progression. The tested compounds enhanced the vegetative growth of pepper plants, indicating there was no phytotoxicity on pepper plants in greenhouse conditions. DMAPAPP and Ru-DMAPAPP also activated antioxidant defense mechanisms that are enzymatic, including peroxidase, polyphenole oxidase, and catalase, and non-enzymatic, such as total soluble phenolics and total soluble flavonoids. DMAPAPP and Ru-DMAPAPP also promoted the overexpression of CaCu-SOD and CaAPX genes. However, CaGR and CaMDHAR were downregulated. These results demonstrate how DMAPAPP and Ru-DMAPAPP could be employed as a long-term alternative control approach for Fusarium wilt disease as well as the physiological and biochemical mechanisms that protect plants.

Benzoic Acid and Its Hydroxylated Derivatives Suppress Early Blight of Tomato (Alternaria solani) via the Induction of Salicylic Acid Biosynthesis and Enzymatic and Nonenzymatic Antioxidant Defense Machinery.

Tomato early blight, caused by Alternaria solani, is a destructive foliar fungal disease. Herein, the potential defensive roles of benzoic acid (BA) and two of its hydroxylated derivatives, ρ-hydroxybenzoic acid (HBA), and protocatechuic acid (PCA) against A. solani were investigated. All tested compounds showed strong dose-dependent fungistatic activity against A. solani and significantly reduced the disease development. Benzoic acid, and its hydroxylated derivatives, enhanced vegetative growth and yield traits. Moreover, BA and its derivatives induce the activation of enzymatic (POX, PPO, CAT, SlAPXs, and SlSODs) and non-enzymatic (phenolics, flavonoids, and carotenoids) antioxidant defense machinery to maintain reactive oxygen species (ROS) homeostasis within infected leaves. Additionally, BA and its hydroxylated derivatives induce the accumulation of salicylic acid (SA) and its biosynthetic genes including isochorismate synthase (SlICS), aldehyde oxidases (SlAO1 and SlAO2), and phenylalanine ammonia-lyases (SlPAL1, SlPAL2, SlPAL3, SlPAL5, and SlPAL6). Higher SA levels were associated with upregulation of pathogenesis-related proteins (SlPR-1, SlPR1a2, SlPRB1-2, SlPR4, SlPR5, SlPR6), nonexpressor of pathogenesis-related protein 1 (SlNPR1), and salicylic acid-binding protein (SlSABP2). These findings outline the potential application of BA and its hydroxylated derivatives as a sustainable alternative control strategy for early blight disease and also deciphering the physiological and biochemical mechanisms behind their protective role.