Mecanismo de ação de óleos essenciais na redução da severidade da pinta preta do tomateiro

Abstract

Currently, the use of alternative tools to chemical control has become one of the most sustainable and eco-friendly options for crop protection against phytopathogens. Tomato production is frequently restricted by early blight (EB), a highly destructive disease caused by the phytopathogenic fungus Alternaria spp. Based on this problem, the present study aimed to evaluate the effect of essential oils (EOs) and the biological control agent (BCA) Bacillus amyloliquefaciens MBI600 for control of EB. The effect of antifungal activity, resistance induction, growth and productivity of the EOs of thyme (Thymus vulgaris), lemongrass (Cymbopogon citratus), tea tree (Melaleuca alternifolia) and BCA MBI600 were tested for control of A. linariae in tomato plants. Under in vitro conditions, the mycelial growth of A. linariae was strongly inhibited at 100, 100 and 87.47 % when applied thyme EO (2000 ppm), lemongrass EO (2000 ppm), and BCA MBI600 (500 ppm), respectively. The treatment with thyme EO (0.89%) and lemongrass EO (1.11%) had the lowest percentage of conidia germination. Tea tree EO showed reduced antifungal activity on A. linariae. The percent of infected leaf area at eight days after inoculation (DAI), sprayed with thyme EO and BCA BMI600, was 46.78 and 66.29 % lower than the plants only inoculated. The final disease severity (70 DAI) in the treatment with the BCA MBI600 (36.74%) and thyme EO (42.00 %) was significantly lower than the control treatment (68.81%) (P ≤ 0.05). Foliar spraying with BCA MBI600 and thyme EO induced resistance in tomato plants, with increased activity of defense-related enzymes; peroxidase, polyphenol oxidase and β-1,3-glucanase, showing maximum activity at 144, 192 and 192 hours after inoculation, respectively, and to a minor extent phenylalanine ammonia-lyase. After BCA MBI600 and thyme EO application, callose deposition, lignin, and phenol accumulation in infected tissues by A. linariae improved, whereas the BCA MBI600 increased plant height, number of leaves, and yield. In this study, BCA MBI600 and thyme EO showed high antifungal activity in vitro conditions. Furthermore, under in vivo conditions, both BCA MBI600 and thyme EO stimulated the defense system of tomato plants infected by A. linariae, which was associated with reduced severity of EB. These results indicate that thyme EO and BCA MBI600 are potential tools in tomato EB disease management.