Ronice Alves Veloso

Composição e fungitoxicidade do óleo essencial de capim citronela em função da adubação orgânica

The objective of this work was to evaluate the influence of organic fertilization on the content and composition of the essential oil of citronella grass (Cymbopogon nardus), as well as to assess the fungitoxicity of this oil to the mycelial growth of the fungi Didymella bryoniae, Colletotrichum gloeosporioides, and Amphobotrys ricini. The extraction of the essential oil was done by hydrodistillation in plants cultivated with four doses of organic fertilizer (0, 3, 6, and 9 kg matured cattle manure per hole), and the identification of the chemical compounds was done by gas chromatography/mass spectroscopy. To evaluate the inhibition of mycelial growth, the experiment was installed in a completely randomized design in a factorial arrangement. Seven aliquots of essential oil were tested (0, 5, 10, 15, 20, 25, and 30 µL) in five evaluating times, with four replicates. The contents of the essencial oil in citronella grass were note affected by organic fertilization, and the oil includes 24 chemical compounds, among these monoterpenes and sesquiterpenes, with higher concentrations of the compounds citronellal, β-citronellol, geraniol, and elemol. The essential oil of citronella grass has higher inhibition effect on Amphobotrys ricini, when compared to the fungi Didymella bryoniae e Colletotrichum gloeosporioides.

Teor e composição do óleo essencial de quatro acessos e duas cultivares de manjericão (Ocimum basilicum L.)

The objective of this study was to evaluate the essential oil chemical composition and content of four wild accessions of basil (Ocimum basilicum L.), from different geographical regions, and two commercial cultivars grown under the same edaphoclimatic conditions. The seeds of the accessions were collected in the municipality of Gurupi, state of Tocantins (GUR), and Monte Alegre, state ofGoias (MAL, MVE and FPS), and the seeds of the commercial cultivar of purple basil (MR) were acquired in the Gurupi market and the seeds of the commercial cultivar Maria Bonita (MB) were provided by the Garden of Medicinal Plants of the Federal University of Lavras. The seeds were planted in pots with a capacity of ten liters using as substrate soil from earth works and cattle manure in the proportion of 2:1. The essential oil was obtained by hydrodistillation using a Clevenger-type apparatus, and the identification and the relative percentage of the compounds of the essential oil were performed by Gas Chromatography coupled to Mass Spectrometry Detector. Thirty-nine compounds were identified in the essential oils obtained, which were divided into monoterpenes, sesquiterpenes and phenylpropanoids. In the cultivars MB and MR, the major compound was linalool, and in the wild accessions (MAL, GUR, FPS and MVE) it was the (E)-methyl cinnamate. The highest content of essential oil was obtained from the cultivar Maria Bonita (3.77%).

Enzymatic Activity in Essential Oil-Treated and Pathogen-Inoculated Corn Plants

Bipolaris maydis and Exserohilum turcicum are important fungal pathogens that cause leaf blight in corn whose control have been difficult. Essential oils are a promising and environmentally friendly alternative for disease management, but the mechanisms of action remain poorly studied. Here, we aimed to assess the effect of B. maydis and E. turcicum as well as the essential oil of Morinda citrifolia in the activity of plant defense enzymes in corn plants. Experiments were carried out in a completely randomized design with three replications and six treatments as they follow: (T1): corn plants inoculated with B. maydis; (T2): corn plants inoculated with E. turcicum; (T3): corn plants treated with essential oil of M. citrifolia (0.25%) and inoculated with B. maydis; (T4): corn plants treated with essential oil of M. citrifolia (0.25%) and inoculated with E. turcicum; (T5): corn plants treated with essential oil of M. citrifolia (0.25%); and (T6): corn plants non-inoculated and treated with distilled water. Protein content (PC) and activities of the enzymes ascorbate peroxidase, catalase, chitinase (CHI), peroxidase (POX) and superoxide dismutase (SOD) were assessed. PC was significantly decreased, whereas CHI and SOD activity was higher in T1-T5 compared to T6. T4 and T5 significantly increased POX activity relative to T6. Therefore, our findings suggest that the essential oil of M. citrifolia may play an active role in disease control by activating defense enzymes in corn plants.

Essential Oils for Alternative Teak Rust Control

The objectives of this study were to evaluate the effect of lemon grass, citronella grass, Mexican-tea and noni essential oils on urediniospore germination of Olivea neotectonae, the agent responsible for rust in Teak (Tectona grandis L.f.); to evaluate the phytotoxic effect of these essential oils on teak seedlings; and to evaluate the use of essential oils to control rust in teak plants when preventively and curatively applied. We found that the noni and lemon grass essential oils inhibited 100% of urediniospore germination. On the other hand, the essential oils from noni and lemon grass caused phytotoxicity when applied to seedlings at concentrations of 2000 and 1500 μL L-1, respectively. The major constituents found in lemon grass essential oil were Geranial and Neral, while Octanoic Acid was found in noni oil. Lower values in the area below the rust progress curve were observed with the preventive application of lemon grass and noni essential oils.

Essential Oil of Cymbopogon citratus on the Control of the Curvularia Leaf Spot Disease on Maize

The Curvularia Leaf Spot is becoming more common due to the culture expansion and the low resistance of the cultivated genotypes in tropical regions. Thus, the objective was to evaluate the fungitoxicity of the essential oil of Cymbopogon citratus upon the phytopathogen Curvularia lunata, causative agent of the Curvularia Leaf Spot. There was realized pathogenicity tests of C. lunata in maize plants, phytotoxicity of the essential oil of C. citratus and gas chromatography attached, germination tests of the conidia, and of in vitro inhibition of C. lunata. Also, there were realized tests aiming at verifying the phytopathogen control in vivo. In the pathogenicity tests, there were verified symptoms of the disease in all of the suspensions tested on plants. It was observed that the essential oil concentrations of 7.5 µL mL−1 to 50 µL mL−1 were phytotoxic. The majoritarian chemical components of the essential oil of C. citratus were Geranial (41.46%) and Neral (32.43%). The concentrations of 5 and 7.5 µL mL−1 inhibited 100% of conidia germination. None of the concentrations evaluated effectively inhibited C. lunata mycelial growth in in vitro tests. In the preventive control, the concentration of 7.5 µL mL−1 was sufficient for the reduction of the progress of the disease, however the curative control was not efficient on the tested dosages.