Phytochemical composition of essential oils from aerial parts of sweet basil infected by a mixed infection of tobacco mosaic virus and phytoplasma

Abstract

Ocimum basilicum, commonly known as sweet basil, was found naturally infected showing mosaic mottling and witches’ broom symptoms. Semi-nested PCR using specific primers revealed the presence of a mixed infection of TMV and Candidatus phytoplasma. This study aims to evaluate and compare the phytochemical composition of essential oils from aerial parts produced in sweet basil. The comparison covered uninfected, mixed infected, TMV infected, and phytoplasma infected sweet basil. Thirty different essential oils were isolated and evaluated using gas chromatography-mass spectrometry (GC-MS) analysis. The essential oils produced were grouped into 5 main classes: monoterpenes hydrocarbons, oxygenated monoterpenes, sesquiterpenes hydrocarbons, oxygenated sesquiterpenes and ketones. All classes were severely altered due to TMV and Candidatus phytoplasma infection compared to the control. The pathological stress caused by the mixed infection was significantly higher than each pathogen separately. The monoterpenes hydrocarbons, oxygenated monoterpenes and ketones showed a significant increase in the essential oil percentages induced in the mixed infection than that of single infections. Yet, a significant decrease in sesquiterpenes hydrocarbons and oxygenated sesquiterpenes was reported in the infected plants. Furthermore, α-bergamotene, (+)spathulenol, α bergamotene, δ-guaiene, cubenol, bornyl acetate and 1,3-bis(cinnamoyloxymethyl)adamantane, were found only in healthy plants, while α-pinene, camphene, sabinene, β-pinene, β-myrcene, trans-sabinene hydrate, eugenol and trans-caryophyllene were detected only in infected plants. This study reports the possible metabolic consequences and defense mechanisms that induced in sweet basil due to TMV and phytoplasma infection.