Óleo essencial de limão para controle de Alternaria alternata (Fr:Fr.) Keissler f. sp. citri

Abstract

Concern about fungicide resistance and toxicity has led to the need to explore alternatives for controlling Alternaria Brown Spot (MMA), caused by the fungus Alternaria alternata. The objective of this work was to evaluate the effect of essential oils (EOs), in different concentrations, on the control of MMA. Experiment 1, carried out in vitro, was carried out in a completely randomized design (DIC), in a 2x4x5 factorial scheme, with two control methods (preventive and curative), four lemon genotypes for EO extraction (Amber, Eureka, Harvey and Siciliano) and five concentrations of EO (0, 2, 4, 8 and 16 μL ml-1), with three replicates per concentration. In experiment 2, carried out in vivo, it was installed in DIC, in a 2x4x3 factorial scheme, with three replications, two control methods (preventive and curative), four lemon genotypes for EO extraction and three EO concentrations (0, 8 and 16 L ml-1). In the preventive control method, approximately 1 ml of different concentrations of the solution with EO + Tween 80 was applied, after two hours, 1 ml of the pathogen solution was applied. For the curative control test, 1ml of the pathogen solution was applied to the leaves, and after 24h, the solution with EO + Tween 80 was applied. Severity assessments were carried out for seven days after inoculation of the fungus. Using the severity data, the Area Below the Disease Progress Curve (AACPD) was calculated. The data were subjected to analysis of variance, when significant for control methods and lemon genotypes for EO extraction, they were compared using the Tukey test, at 5% probability. When significant for concentration, they were analyzed by regression. The preventive control method, in the in vitro experiment, is better in controlling the fungus Alternaria alternata. The Amber genotype stood out in controlling the fungus, both in preventive and curative methods. The EOs of the four genotypes, in both application methods, provided greater control of the fungus with increasing EO concentration. In the in vivo experiment there was no difference between the control methods. The EOs extracted from all genotypes provided greater control when the highest concentration was used (16μL ml-1). The Amber genotype showed the greatest control of the fungus.