Vincenzo De Feo-l, Francesco De Simone-l and
Felice Senatore-2
1- Centro Interdipartimentale di Chimica, Biologia e Tecnologia
Farmaceutiche, Università degli Studi di Salerno, Piazza Vittorio
Emanuele, 9 - 1-84084 Penta di Fisciano (Salerno) Italy;
2- Dipartimento di Chimica delle Sostanze Naturali, Università
"Federico II", via D. Montesano, 49 - 1-80131 Napoli, Italy.
Volatile compounds have been reported to have allelopathic properties in plant-plant, plant-micro-organisms, and plant-insects interactions (1). Such compounds may be present in various phases of interaction: their presence in the aerial parts make it able of forming vapour clouds of volatiles around the plants; the presence in the soil surrounding the plants, and the ability to remain in the dry soil until micro-organism decomposition, permit their transport into plant cells through the waxy coatings of seeds and roots, with related effects on the seed germination of the ground flora in the vicinity (2).
In a series of studies concerning the in vitro interactions between plants, our research group is carrying out a study on the allelopathic properties of Ruta graveolens L. (rue), a plant used medicinally from centuries. Several species, in fact, that have been widely used in medicine, exert also significant allelopathic activities.
In previous works, we have isolated, from the aqueous extract of rue, some flavonoids and coumarins, with a high inhibitory activity on seed germination and radicle elongation of radish (3). In addition, a simple rue infusion can be used, in greenhouse experiments, in the control of some common weeds (4,5).
In this paper we have evaluated the potential allelopathic activity of the essential oil of R. graveolens and of its constituents.
The essential oil was obtained hy hydrodistillation of the aerial parts of R. graveolens and was analysed by GC and GC/MS. Forty-two compounds were identified in the oil, with prevalence of ketone compounds. 2-Undecanone (methyl-nonyl ketone) and 2-nonanone (methyl-heptyl ketone) constitute the main components; terpenoids are represented mainly by limonene, a-pinene and l,8-cineole.
The essential oil and its constituents decected in amounts greater than 1% were assayed in different concentrations (from 10-3] to 10-6 M for the pure compounds) on seed germination and radiclc elongation of radish (Raphanus sativus L. cv 'Saxa'), both in the light and in darkness.
The essential oil and some of the pure compounds. namely 2-nonanol, 1,8-cineole and methyl salycilate, showed a significant and dose-dependent inhihitory activity both of seed germination and radical elongation of radish. Ketone compounds, on the contrary, seems to show not any allelopathic activity.
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