Atividade nematicida de óleos essenciais de plantas do semiárido mineiro

Abstract

The gall nematodes cause great losses to several economically important crops. One of the most used techniques for its control is the use of nematicides. However, due to its high toxicity and the possibility of contamination of the environment, alternative sources using products of natural origin have been extensively studied. An example is the use of essential oils that constitute a potential alternative to synthetic chemical nematicides. Thus, in order to contribute to the development of new nematicidal products that are efficient and less toxic to humans and the environment, the essential oils produced by plants located in the semi-arid region of Minas Gerais were studied, as well as the potential and activity of oils and their chemical constituents against Meloidogyne javanica. In the first chapter, collections of plants and extractions of their essential oils were carried out using the hydrodistillation technique, followed by analysis by gas chromatography coupled with mass spectrometry (CG-EM) for the characterization of chemical constituents. Subsequently, in vitro tests were carried out against juveniles of the second stage (J2) of M. javanica in the presence of the obtained oils and the major substances (citral, 2-dodecanone and 2-decanone) present in the oil of Cymbopogon citratus which showed greater nematicidal activity. In order to determine the concentration of the chemical components of the oil of C. citratus that caused death of 50% (LC50) or more in nematodes, preliminary tests were carried out in different concentrations: 0, 500, 700, 900, 1100 μg/mL for 2-decanone and 2-dodecanone. 0, 500, 550, 600, 650, 700 μg/mL for citral. The products were diluted in Tween® 80 to 0.01 g mL-1 Water, Tween® (polysorbate) and carbofuran, a commercial nematicide, were used as controls. The experimental design was completely randomized with six replications. The essential oils data were submitted to analysis of variance and the averages were grouped by the Scott-Knott test at 5%. In the other tests, the concentrations were subjected to regression adjustment and averages compared to controls using the Dunnett test. Such substances promoted a linear increase in mortality and immobility of J2 with increased concentrations and a linear reduction with increased concentrations on the outbreak of J2 of M. javanica. In the second chapter, C. citratus oil and citral (a substance that showed better nematicidal activity in the in vitro tests for the control of M. javanica) were tested in the greenhouse in the ‘babá de verão’ lettuce culture (butter). The design was in randomized blocks with six repetitions in the concentrations of 0, 260, 521, 700 and 1000 μg/mL of the essential oil of C. citratus and 0, 500, 550, 600, 650, 700 μg/mL for the citral. The controls were water, Tween ®80 at 0.01 g mL-1and carbofuran. After 35 days of planting the seedlings, a suspension was applied containing 4000 eggs plus possible J2 of M. javanica along with emulsions, freshly prepared, of the oil of C. citratus and citral. Such emulsions were distributed in the soil in four holes equidistant from the plant. The data obtained were submitted to the regression adjustment and the means compared to the controls using the Dunnett test. The essential oil and citral affect the reproduction of M. javanica in ‘babá de verão’ (butter) lettuce plants.