EFFECT OF NITROGEN RATES ON ESSENTIAL OIL CONTENT OF TWO TUNISIAN FENNEL (Foeniculum vulgare Mill.) ACCESSIONS

Two accessions of fennel (Foeniculum vulgare Mill) were collected from two Tunisian localities (Sahel and Sfax) and grown in field trials under four rates of nitrogen (50, 100, 150 and 200 kg/ha) to evaluate their essential oil yield and composition in response to this nutrient. The essential oil from seeds was extracted by hydrodistillation and analyzed by gas chromatography (GC) and gas chromatography–mass spectrometry (GC-MS). The essential oil yield presented significant differences between the two fennel seed accessions studied. The highest seed yield per hectare among the accessions belonged to Sfax accession, obtained on 50 and 150 kg/ha nitrogen fertilization. Twenty nine compounds were identified in all of the examined essential oils. Trans-anethole was the major compound in Sahel accession (67.4–77.0%) followed by nonanal (0.2–15.5%), fenchone (8.7–11.1%) and limonene (5.0–6.8%). The major compounds detected in the seeds essential oils of Sfax accession are trans-anethole (72.3–79.3%), limonene (6.2–11.0%), fenchone (4.2–10.8%) and estragole (3.2–9.2%). The highest essential oil percentage was obtained at 50 kg/ha nitrogen fertilization for Sahel accession and at 200 kg/ha nitrogen fertilization for Sfax accession.