Action of citronella (Cymbopogon nardus L) essential oil on the pathogen Lasiodiplodia theobromae in bunches of grapevine cv. ‘Itália’

ABSTRACT Presence of Lasiodiplodia theobromae (dry rot) in vines established in irrigated areas of the Brazilian semiarid region has shown to be highly aggressive when infecting several parts of the plants. Essential oils have shown efficiency in controlling diseases, both by the fungitoxic action, inhibiting mycelial growth and spore germination, and by the presence of eliciting compounds. Thus, the objective of this study was to obtain control of L. theobromae by using citronella oil (Cymbopogon nardus L) at different levels. Mycelial growth of L. theobromae was analyzed in Petri dishes containing potato-dextrose-agar medium supplemented with essential oil at the following concentrations: 0; 0.25; 0.5; 1.0; 1.5 and 2.0%. To evaluate the direct effect of the essential oil on the development of the disease, grape bunches were inoculated with the pathogen and, after 4 h, sprayed with solutions containing the same concentrations described above; subsequently, in order to evaluate the potential of the essential oil in the preventive treatment, the same treatments were applied in grape bunches 4 hours before inoculation. Citronella oil at all tested concentrations was capable of inhibiting the mycelial growth of L. theobromae by 100%. For the healing treatment, considering incidence, 0.25% citronella reduced by 38% the infection in berries of grape bunches inoculated with L. theobromae and was capable of reducing the disease severity by 56%. As regards the preventive treatment, 0.25% citronella oil reduced by 52% the infection in berries of grape bunches cv. ‘Itália’, reducing the disease severity by 66.3%. These results lead to the conclusion that 0.25% was the best concentration tested for disease control with citronella essential oil.