Ovicidal activity of essential oils and their components on phytoparasitic nematodes.

Propagation and survival of the most economically relevant phytonematode species mainly rely on eggs, due to a prolonged survival and presence of protective structures such as gelatinous matrices or cysts. Therefore, eggs represent a main target of any innovative nematode control tools, such as potential formulates based on essential oils (EOs) or their active components. In this study, a large number of EOs and, at a less extent, of their single constituents have been tested at different concentrations and exposure times on the egg masses of the root-knot nematode Meloidogyne incognita and the encysted eggs of cyst nematodes Globodera rostochiensis and Heterodera carotae. The ovicidal activity of tested EOs largely varied according to their composition and source plant. The EOs from Ruta graveolens and Cinnamomum zeylanicum were highly active on M. incognita eggs, as causing 76 and 88% mortality rates, respectively, since after a 24-hour egg exposure to 500 μg mL-1 EOs’ solutions Adversely, a lower egg hatch inhibition was observed for the EOs from Schinus molle and Pelargonium graveolens. Egg hatch inhibition also varied among the EOs from the same plant genus, as in a comparative study on two different Monarda species the ovicidal activity was always significantly higher for M. dydima than for M. fistulosa EO. A study on single EOs’ components revealed a strong activity on M. incognita eggs for carvacrol, as determining an almost complete egg mortality after a 48-hour exposure of egg masses to a 500 μg mL-1 carvacrol solution, as well as for thymol. Adversely, a low activity on root-knot nematode eggs was recorded for g-terpinene and o-cymene. The activity on cyst nematode eggs varied either among the EOs and the nematode species. The EO from S. molle was much more suppressive on H carotae than on G. rostochiensis eggs, whereas the E. caryophillata EO exerted a similar activity on both nematode species. Data demonstrated that effect of EOs is extended to all the infective and propagative stages of phytonematode species, as confirming the potential of these plant compounds for the formulation of new nematicides.