Control of dry rot (Lasiodiplodia theobromae) in bunches of grapevine cv. Itália using essential oil and chitosan

ABSTRACT

Among fungal infections that affect the grapevine post-harvest is dry rot caused by Lasiodiplodia theobromae, which leads to losses greater than those in the field since they are added to the costs of harvest, transport and storage. Natural products have been used to control plant diseases, showing efficiency in reducing the use of pesticides. Thus, this study aimed to obtain control of dry rot by using alternative products. Mycelial growth of L. theobromae was analyzed on Petri plates containing PDA medium supplemented with the following products: citronella, clove and mint oil at the concentrations of 1.0% and 1.5%, and chitosan (1.5%). Control was a plate with PDA medium with no product addition. To evaluate the healing effect of oils on dry rot development, bunches of grapevine cv Itália were inoculated with the pathogen and, after 4 h, sprayed with the concentrations of 1.0% and 1.5% clove, citronella and mint oil solution; 1.5% chitosan solution, and water (control). Subsequently, to evaluate the protective potential, bunches of grapevine cv. Itália were subjected to the same treatments and inoculated, after 4 hours, with L. theobromae. For the assessment of inoculation time, bunches of grapevine cv. Itália were sprayed with solution of the essential oils: clove (1.5%) and citronella (1.0% and 1.5%), and water (control), and inoculated after 24, 48, 72 or 96 h with the fungus L. theobromae. Mint and citronella oils, at all concentrations, were capable of inhibiting the mycelial growth of L. theobromae. Essential oils and chitosan were effective in reducing the incidence of dry rot in bunches of grapevine cv. Itália. However, regarding the severity alone, citronella and mint oils, at the concentration of 1.5%, retained the ability to reduce the disease by 30 and 29.2%, respectively. The inoculation time influenced the disease incidence and severity. The longer the time for the material to be inoculated, the higher the incidence and the severity of the disease.

Keywords
Vitis sp; natural product; fungal disease control