Antifungal activity and control of the early blight in tomato through tea tree essential oil

Abstract

One of the main leaf diseases of tomato is the early blight, caused by the fungus Alternaria solani. The use of essential oils could be an alternative for controlling by acting plant defense against phytopathogens. The objective was to evaluate the antifungal, the early blight control, and the activity of defense enzymes in tomato treated with tea tree (Melaleuca alternifolia) essential oil. Aiming to evaluate the mycelial growth and sporulation of the pathogen, mycelial discs were placed in Petri dishes with 0, 500, 1000, 1500, 2000, and 2500 μL L−1 of essential oil, and an additional treatment with fungicide (azoxystrobin + diphenoconazole). The treatments were applied onto the second pair of leaves of tomato plants grown in a greenhouse, and after three days the pathogen was inoculated in the second and third pairs of leaves. Severity was expressed through the area under the disease progress curve (AUDPC). The peroxidase, polyphenoloxidase and phenylalanine ammonia-lyase activities were evaluated with the concentration of 1500 μL L−1. Mycelial growth showed a linear decrease as concentrations increased. In the treated leaves, the 1500 μL L−1 concentration showed the most reduction in AUDPC, corresponding to 53%, whereas in the untreated leaves, the most effective concentration was 2000 μL L−1 with 42% inhibition. An increase in peroxidase and phenylalanine ammonia-lyase activities were observed in the tomato leaves. Tea tree essential oil can be an alternative for the control of early blight in tomato.