Óleos essenciais no controle da ferrugem asiática da soja Phakopsora pachyrhizi Syd. & P. Syd.

Abstract

The objective of this work was evaluating the potential of essential oils in the control of the Asian soybean rust caused by plant pathogen P. pachyrhizi. The experiment was carried out in two stages. In the first, in Petri dishes contends 10 mL of agar-water medium and essential oils from Corymbia citriodora,Cymbopogon nardus, Azadirachta indica or Thymus vulgaris in the concentrations of 1%, 0.5%, 1% and 0.3%, respectively for each oil, 100µL of urediniospores were added in the concentration of 5mg/mL of water, incubated by 4 hours for 25ºC and appraised the germination. In second trail in green house, the oils, in the same concentrations, were applied in soybean plants (cultivars MG/BR46 (Conquista) and Suprema) 7 days before and 15 and 30 days after the inoculation. The appraised parameters were presence and number of uredia for cm2 of foliar area. It was also collected leaflets to preparation of samples to Scanning Electron Microscopy (SEM). It was possible to verify that the oils in the used concentrations inhibited 100% the urediniospores germination in medium agar-water. In green house it was observed that all the oils delayed the evolution of the disease when compared with the control, and the severity of the disease was reduced in average from 34.6 to 60.7% on the cultivar MG/BR46 (Conquista) and from 45.7 to 62.3% on the cultivar Suprema in relation to the control. In the SEM it was observed that the urediniospores were withered, on soybean plants where T. vulgaris oil was spread. For the other treatments it was just observed reduction in the size of the uredias. We can infer that the used essential oils have potential to reduce the attack of the P. pachyrhizi, agent of the Asian soybean rust.