Phytotoxic effect of caraway essential oil and its main compounds against germination of spring wheat and two weed species

Increased interest in using biological methods of crop protection has led to research on the various plant's allelopathic potential. Essential oils show phytotoxic properties that can be used to produce alleloherbicides (botanical herbicides), i.e., natural substances to control weeds. The most frequently analyzed effect of essential oils is their influence on the seed germination process and seedlings' development and growth. This study aimed to investigate the phytotoxic potential of oil in water (o/w) solutions of caraway oil and its main components: carvone and limonene, on germination of spring wheat (Triticum aestivum, cv. Tybald), wild oats (Avena fatua), and chamomile (Matricaria chamomilla).

Caraway oil was rectified under reduced pressure to separate the essential oil into fractions containing carvone and limonene. GC-FID-MS analyzes of volatile compounds were performed on a Trace GC Ultra gas chromatograph connected to a DSQ II mass spectrometer (Thermo Electron). Simultaneous GC-FID and MS analysis were carried out using the MS-FID (SGE Analytical Science) splitter.

The Petri dish experiment was performed in the laboratory, in four series and three repetitions. Five doses of caraway oil: 0.6; 1.0; 1.4; 2.8; 4.3 mg cm^-3, carvone: 0.2; 0.6; 1.2; 1.7; 2.9 mg cm^-3 and limonene: 0.1; 0.3; 0.7; 1.0; 1.4 mg cm^-3 were used. Twenty seeds of the tested species were placed on two layers of filter paper in each dish. The filter paper was previously soaked with 7 g of an appropriate o/w solution. The seeds were allowed to germinate for seven days in the dark at room temperature (± 25 ° C). After this time, seedlings were counted, and the length of their roots and stems were measured.

It was found that caraway oil and its fractions containing the dominant ingredients: carvone or limonene, inhibit the germination of spring wheat and both weeds. The most sensitive to caraway oil was chamomile. In turn, spring wheat was the least sensitive to caraway oil. Limonene displayed the smallest effect on the germination of the tested plant species.