Prospecção de Geraniol synthase (GES) em espécies aromáticas e uso do óleo de kenaf para controle da ramulose no algodoeiro

Abstract

Cotton stands out as a high value textile plant in the world market due to the quality of its fibers and the commercial derivatives that the plant produces. Ramulose is a disease that causes great damage to this crop, caused by the fungus Colletotrichum gossypii South var. cephalosporioides Costa, mainly affects young leaves, the most common symptoms being the darkening and necrosis of leaves and branches, which may compromise the whole development of the plant. Extracts and vegetable oils have been studied as an alternative to control pests and diseases such as ramulose in crops. These have as main constituents the secondary compounds, chemicals known as phytochemicals, terpenoids, alkaloids and glycosides. Among these the geraniol, monoterpene that stands out for its fungicidal property. Kenaf (Hibiscus cannabinus) belongs to the family Malvaceae and is rich in compounds known as polyphenols, alkaloids, tannins and essential oils, also being a promising source of fungicidal oil. This work aimed to analyze the effect of oils and extracts on the development of the fungus C. gossypii, which causes ramulose, by means of two researches: In the first one, we sought to prospect Geraniol synthase, the precursor enzyme of geraniol, in aromatic species, for means of molecular analyzes via PCR and qPCR, besides phytopathological tests, in order to evaluate the geraniol expression and the effectiveness of its extracts and vegetable oils in the prevention and control of ramulose; The second study evaluated the effect of Kenaf oil on the development of fungus C. gossypii under laboratory conditions. In order to carry out the first research eleven aromatic species were evaluated, among them M. pulegium, O. basilicum, O. majorana and R. officinalise, which presented satisfactory levels of expression of this enzyme in the molecular assays, being selected for bioassays in vivo against C. gossypii. O. basilicum, M. pulegium and O. majorana oils, at 2000 ppm concentration, were tested in vivo and their preventive and curative actions compared to commercial fungicide. There was effective control of the oils O. basilicum and M. pulegium under ambient conditions, and M. Polegium was distinguished with D.S.I. around 30%, lower value than that presented by the commercial fungicide (40%). These results indicate that the use of aromatic species can be an effective alternative for the treatment of ramulose, with the advantages of being a low cost method and not presenting risks of environmental contamination. In addition, the genetic characterization of aromatic species is an important source of information to expand the use of natural resources, allowing new materials that hold genes of interest to be found and serve as environmental conservation strategies. In the second study, phytopathological tests were performed on isolate 287 of C. gossypii on the effect of Kenaf oil at concentrations of 25, 50 and 75 μl / 1 ml. It was verified by regression analysis that there was no reduction in the mycelial growth of C. gossypii in the oil concentrations adopted in this work. The data presented by fungus growth, fungistatic effect and spore production did not reveal a statistical difference between the treatment with oil and control. Based on the composition of kenaf oil, rich in fungicidal ingredients, even this oil lacking control over C. gossypii in the present study, it is believed that in higher concentrations this oil may exert an effect on this pathogen.