Effectiveness of essential oils for postharvest control of Phyllosticta citricarpa (citrus black spot) on citrus fruit

Abstract

The in vitro and in vivo control of Phyllosticta citricarpa (citrus black spot, CBS) on citrus fruits was evaluated using 14 essential oils (EOs) extracted from Uruguayan native plants. In vitro, volatile components of Chenopodium ambrosioides completely inhibited fungal growth. The dilution agar test showed that fungus reproduction was completely inhibited by Conyza bonaerensis essential oil (EO). The other 12 EOs tested showed high inhibition after 10–15d, presenting fungistatic effects. In vivo, assays were performed on fruit of lemon [Citrus limon (L.) Burm] and Valencia orange [Citrus sinensis (L.) Osbeck] in order to evaluate the effects of liquid and volatile EO phases on reproduction. Typical lesions of CBS without reproductive structures were exposed to Ch. ambrosioides and C. bonaerensis EOs for 20 d at 27°C and cycles of 16h light and 8h dark. The volatile components of Ch. ambrosioides were able to control 100% of P. citricarpa reproduction in orange and lemon fruit. The growth of other fungi such, as Colletotrichum gloeosporoides and Fusarium sp., was also inhibited. Nevertheless, the liquid phase was not effective to control the pathogen. In another test, carton boxes with 20 fruits, each presenting typical CBS symptoms, but without the presence of reproductive structures, were exposed to 0.01 and 0.05% of Ch. ambrosioides EO (w/v). The fruits were stored at 5°C for 20d and then kept for 7d at room temperature. A 40% reduction of reproduction was observed in citrus fruit exposed to 0.05% of EO. GC–MS analysis of EOs showed that Ch. ambrosioides EO was composed of 76% monoterpene compounds (49 and 27% of oxygenated and hydrocarbons, respectively), while C. bonaerensis EO presented 17% monoterpenes and 10% sequisterpenes.