Chemical Composition and Phytotoxic Activity of the Volatile Oil of Invasive Xanthium italicum Moretti from Xinjiang
2013-08-20
China is one of the many countries seriously affected by biological invasion. Among the various exotic species, Italian cocklebur (Xanthium italicum Moretti), a herbaceous annual weed belonging to the genus Xanthium (family Asteraceae) that is represented by 25 species distributing throughout Eurasia and America, was first spotted in Beijing. In the past two decades, the exotic plant has quickly expanded to six provincial or autonomous regions.
X. italicum is a very competitive weed; once established, X. italicum is often found to form dense monocultures as long as light, moisture and nutrition are sufficient, which consequently results in adverse impacts on native plant communities. Xanthium plants are found to be very difficult to control either chemically or manually. Previous study showed that aerial parts of X. italicum in an air tight container could inhibit root elongation of radish by 79%, implying that this plant can release biologically active VOCs into the environment to affect other plants’ growth. This phenomenon was further studied by evaluating the phytotoxic effects of X. italicum essential oil against two dicot plants, amaranth (Amaranthus mangostanus L.) and lettuce (Lectuca sativa L.), and two monocot plants, wheat (Triticum aestivum Linn) and ryegrass (Lolium multiforum), and analyzing the chemical composition of the oil in this research.
Among the four test species, amaranth was the most sensitive plant, 0.5µl/mL essential oil application resulted in a 50% reduction on root elongation, and 2.5 µl/mL essential oil almost completely inhibited its seedling growth. Wheat was the least sensitive species, whose root growth was reduced to 36% of control by 5 µl/mL essential oil. The essential oil exerted moderate inhibitory effect on both lettuce and ryegrass. Compared to a commercial herbicide–Harness, X. italicum oil exhibited stronger phytotoxicity on amaranth, lettuce and wheat, but weaker activity on ryegrass.
The chemical composition of the essential oil isolated by hydrodistillation from the aerial parts of X. italicum Moretti was analyzed by GC/MS. Thirty two compounds were identified, representing 94.89% of total oil, which was found to be rich in monoterpene hydrocarbons (60.71%). The main constituents of the oil were limonene (51.61%), germacrene B (6.98%), δ-cadinol (5.94%), β-pinene (5.23%), α-caryophyllene (5.1%) and bornyl acetate (3.15%). Bioassay revealed the dominant constituent–limonene, was unlikely the responsible phytotoxic compound due to its low biological activity; rather, there might be other oil constituent(s) that either act alone, or work together, and possibly assisted by synergistic effect, to display the phytotoxic activity.
The result suggested that X. italicum might produce allelopathic VOCs to facilitate its invasion success. This is the first report on the phytotoxic activity and the chemical composition of the essential oil of X. italicum Moretti from China. The result was published in Journal of Arid Land in September 2013, 5(3): 324-330.
X. italicum is a very competitive weed; once established, X. italicum is often found to form dense monocultures as long as light, moisture and nutrition are sufficient, which consequently results in adverse impacts on native plant communities. Xanthium plants are found to be very difficult to control either chemically or manually. Previous study showed that aerial parts of X. italicum in an air tight container could inhibit root elongation of radish by 79%, implying that this plant can release biologically active VOCs into the environment to affect other plants’ growth. This phenomenon was further studied by evaluating the phytotoxic effects of X. italicum essential oil against two dicot plants, amaranth (Amaranthus mangostanus L.) and lettuce (Lectuca sativa L.), and two monocot plants, wheat (Triticum aestivum Linn) and ryegrass (Lolium multiforum), and analyzing the chemical composition of the oil in this research.
Among the four test species, amaranth was the most sensitive plant, 0.5µl/mL essential oil application resulted in a 50% reduction on root elongation, and 2.5 µl/mL essential oil almost completely inhibited its seedling growth. Wheat was the least sensitive species, whose root growth was reduced to 36% of control by 5 µl/mL essential oil. The essential oil exerted moderate inhibitory effect on both lettuce and ryegrass. Compared to a commercial herbicide–Harness, X. italicum oil exhibited stronger phytotoxicity on amaranth, lettuce and wheat, but weaker activity on ryegrass.
The chemical composition of the essential oil isolated by hydrodistillation from the aerial parts of X. italicum Moretti was analyzed by GC/MS. Thirty two compounds were identified, representing 94.89% of total oil, which was found to be rich in monoterpene hydrocarbons (60.71%). The main constituents of the oil were limonene (51.61%), germacrene B (6.98%), δ-cadinol (5.94%), β-pinene (5.23%), α-caryophyllene (5.1%) and bornyl acetate (3.15%). Bioassay revealed the dominant constituent–limonene, was unlikely the responsible phytotoxic compound due to its low biological activity; rather, there might be other oil constituent(s) that either act alone, or work together, and possibly assisted by synergistic effect, to display the phytotoxic activity.
The result suggested that X. italicum might produce allelopathic VOCs to facilitate its invasion success. This is the first report on the phytotoxic activity and the chemical composition of the essential oil of X. italicum Moretti from China. The result was published in Journal of Arid Land in September 2013, 5(3): 324-330.