The nematicidal activity of hydrolate by-products from the semi industrial vapor-pressure essential oil extraction of selected aromatic plant species (commercial: Lavandula × intermedia Emeric ex Loisel. var. super, Thymus vulgaris L., T. zygis Loefl ex L. and experimentally pre-domesticated: L. luisieri (Rozeira) Rivas-Martínez) was investigated against the root-knot nematode Meloidogyne javanica by in vitro and in vivo bioassays. Liquid-liquid extraction of hydrolates yielded the corresponding aqueous and organic fractions which were biological and chemically studied. Hydrolates from L. × intermedia var. super, L. luisieri, T. vulgaris, and T. zygis showed strong in vitro nematicidal effects against M. javanica (J2 mortality and suppression of egg hatching). In the case of the Thymus species, the active components were found in the organic fraction, characterized by thymol as major component. Conversely, the nematicidal activity of L. × intermedia var. super and L. luisieri remained in the corresponding aqueous fractions. In vivo tests on tomato seedlings at sublethal doses of the hydrolates/organic fractions induced a significant reduction of nematode infectivity. In pot experiments, all hydrolates tested on tomato plants significantly affect the infection frequency and reproduction rate of the nematode population. This study demonstrates that L. × intermedia var. super, L. luisieri, T. vulgaris, and T. zygis hydrolates could be an exploitable source of potential waste protection products on root-knot nematodes.
Keywords: Lavandin; Lavandula luisieri; Nematicidal activity; Organic fraction; Root-knot nematode; Thymus vulgaris; Thymus zygis; Water residue.