The Effect of Citrus Essential Oils and Their Constituents on Growth of Xanthomonas citri subsp. citri

Abstract

Citrus bacterial canker (CBC) caused by <i>Xanthomonas citri</i> subsp. <i>citri</i> (<i>Xcc</i>), is the most devastating of the citrus diseases worldwide. During our study, we found that Essential oils (EOs) of some citrus cultivars are effective on <i>Xcc</i>. Therefore, it prompted us to determine the plant metabolites responsible for the antibacterial properties. We obtained EOs from some locally cultivated citrus by using a Clevenger apparatus and their major constituents were identified by gas chromatography/mass spectrometry (GC-MS). The effect of <i>Citrus aurantium</i>, <i>C. aurantifolia</i>, <i>Fortunella</i> sp. EOs and their major constituents were evaluated against <i>Xcc</i>-KVXCC1 using a disk diffusion assay. Minimal inhibitory and bactericidal concentration of the EOs and their constituents were determined using the broth microdilution method. <i>C. aurantium</i>, <i>C. aurantifolia</i> Eos, and their major constituents including citral, linalool, citronellal, geraniol, α-terpineol, and linalyl acetate indicated antibacterial effects against <i>Xcc</i>. The <i>C. aurantifolia</i> EO and <i>citral</i> showed the highest antibacterial activity among the tested EOs and constituents with inhibition zones of 15 ± 0.33 mm and 16.67 ± 0.88 mm, respectively. Synergistic effects of the constituents were observed between α-terpineol-citral, citral-citronellal, citral-geraniol, and citronellal-geraniol by using a microdilution checkerboard assay. Transmission electron microscopy revealed that exposure of <i>Xcc</i> cells to citral caused cell wall damage and altered cytoplasmic density. We introduced <i>C. aurantifolia</i> and <i>C. aurantium</i> EOs, and their constituents citral, α-terpineol, citronellal, geraniol, and linalool as possible control agents for CBC.