No abstract

Anthracnose and grapevine leaf spot are the most important fungal diseases of fox grape in Brazil caused by Sphaceloma ampelinum and Pseudocercospora vitis, respectively. Severe attacks of either diseases can affect the yield in the current and subsequent years. Synthetic fungicides are recommended to control these pathogens in the field but may be harmful to the environment and human health over time and select for fungicide‐resistant pathogen populations. Among the new strategies for safe food production, free of pesticide residues, essential oils represent a promising tool to control plant pathogens. The objectives of this study were to evaluate the antifungal activity of the volatile compounds of 26 essential oils on germination of P. vitis and S. ampelinum and of their principal active compounds as bases for development of new technological products. The essential oils of Cinnamomum zeylanicum and Cymbopogon citratus were fungitoxic to P. vitis and S. ampelinum, in vapour and liquid phases, completely inhibiting spore germination. The main compounds found in the essential oils studied were citral, geraniol, eugenol and isoeugenol. All of these, in vapour and liquid phases, were toxic to P. vitis, completely inhibiting spore germination. Citral, in the vapour phase, and citral, eugenol and isoeugenol in the liquid phase, were toxic to S. ampelinum, completely inhibiting spore germination.

Plum leaf scald (PLS) is the main obstacle to plum expansion in Brazil. This disease is caused by Xylella fastidiosa, which colonizes the foregut of xylem‐sap feeding insects and the xylem of the plants. Breeding programmes identified new plum genotypes that showed no leaf scald symptoms in the field and remained negative for X. fastidiosa for at least 10 years. However, the mechanisms that confer this resistance are not fully elucidated. One hypothesis is the emission of volatile organic compounds by the host. Therefore, we investigated the volatile compound profile from six plum genotypes with different resistance levels to PLS. Thirty‐nine compounds were identified. The major constituents in the plum volatile extract were phytol (46.76%) and limonene (2.48%). Cultivar Laetitia presented the highest total alkane content, Simka showed the highest alcohol content, while Fortune and SC13 exhibited the highest concentration of ketones. Cedrol was not detected in susceptible genotypes but was found in the resistant ones, SC7 and SC15. (E,E)‐α‐farnesene was detected in high concentrations in Fortune but was not found in SC13 and SC15. According to principal components analysis, genotypes were divided into four groups based on the similarity of the volatile profile: 1: Fortune and Laetitia; 2: Simka and SC13; 3: SC7; and 4: SC15. This is the first description of leaf volatile chemical components of Prunus salicina, and the putative factor related to resistance in SC7 and SC15 is discussed. We also propose a terpene pathway of the main volatile compounds found.