Exploring Chemical Profiles, Antifeedant, Nematicidal, and Phytotoxic Potentials of Seven Essential Oils From Eucalyptus Species

Leaf essential oils (EOs) of seven Eucalyptus species planted in Southern Tunisia (E. gracilis, E. lesouefii, E. salmonophloia, E. sargentii, E. flocktoniae, E. oleosa, and E. salubris) were screened for their antifeedant, nematicidal, and phytotoxic effects as well as their chemical compositions. The yield of EOs of these species varied from 1.32% +/- 0.38% to 4.92%+/- 0.37%. Using gas chromatography mass spectrometry (GC-MS) analysis, 22 compounds were identified, representing 87.16%-96.83% of the total oil content. The main components found in all EOs were 1,8-cineole (38.71%-70.44%), alpha-pinene (4.40%-8.88%), p-cymene (0.95%-14.99%), pinocarvone (0.17%-3.22%), trans-pinocarveol (1.53%-13.48%), spathulenol (0.18%-5.39%), and globulol (0.22%-6.47%). The insect antifeedant, nematicidal, and phytotoxic effects of these oils against insect pests (Spodoptera littoralis, Myzus persicae, and Rhopalosiphum padi), the root-knot nematode (Meloidogyne javanica), and two plant models (Lolium perenne and Lactuca sativa) were examined. Despite the moderate insect antifeedant activity, the EOs of E. salubris, E. salmonophloia, E. lesouefii, and E. sargentii were the most effective against M. persicae. Significant nematicidal effects were observed for both E. salmonophloia and E. oleosa EOs. Moreover, all Eucalyptus EOs significantly suppressed the root and leaf growth of L. perenne than the root length of L. sativa, indicating that EOs from Eucalyptus possessed an excellent phytotoxic potential.