Óleos essenciais de espécies citrícas no controle da ferrugem asiática (Phakopsora pachyrhizi H. Sydow & P. Sydow) da soja (Glycine max (L.) (Merrill)

Abstract

Soybeans arrived in Brazil via the United States in 1882, and soon expanded throughout the country. Over the years several diseases of high impact in the development and productivity of the culture were established. Among the main ones is the Asian rust (Phakopsora pachyrhizi), which is fast-spreading and which in the last few seasons is caused by high levels of loss and severe damage. Currently its control is made with numerous applications of fungicides, causing what can cause several impacts to the environment, the health of the producer and the balance of ecosystems. In this sense, the objective of this work was to determine the efficiency of the evaluation of the essential oil potential (EO) of four citrus species (Citrus sinensis), (Citrus reticulata), (Citrus vulgaris) and (Citrus paradisi), verifying if its application can be used as an alternative Control of this disease. The work was carried out in the Phytopathology Laboratory and in the greenhouse of the Federal University of the Southern Border, Laranjeiras do Sul-PR. The evaluation of spore germination was performed on microscopic slides containing a 1% agar-water thin layer, on which 30 μL of the spore suspension and 30 μL of each treatment were deposited. These slides were incubated in a humid chamber at 23 ° C for 12 hours when the percentage of germination was determined. Concentrations of 0.1, 0.5, 1 and 2% of each essential oil were used, in addition to the control being distilled water containing 0.1% Tween 20 with five replicates. The induction bioassay of the defense enzymes was conducted in soybean plants under greenhouse conditions. The OE were applied to the first trifolium of each plant and after 72 hours five disks of 1.5 cm in diameter, the first trifolium (treated) and the second (untreated) trifolium of each plant were collected for analysis of carbohydrates, proteins , Peroxidases, polyphenoloxidases and phenylalanine ammonia-lyase in a spectrophotometer. The bioassay to verify the severity of the disease attack was conducted in soybean plants conditioned in a greenhouse. The treatments were constituted of the four citrus species in the concentrations of 0.1 and 0.5% with five replications. After ten days the symptoms were evaluated the severity of the disease according to the proposed diagrammatic scale. The OE of the different citrus species significantly inhibited the spore germination, with prominence for C. vulgaris that at 0.1% already promoted total inhibition. OE promoted an increase in the activity of the enzymes already in the concentration of 0.1%. Higher induction was observed in treated trefoils, indicating local effect. For severity, the trifoliols treated with C. reticulata and C. vulgaris species at concentrations of 0.1 and 0.5% did not present disease development. These results indicate the great potential of essential oil of the citrus species tested for the control of Asian rust in the soybean crop.