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Allelopathy is a mechanism to achieve a competitive edge among plant species growing in close proximity to one another. It has been shown that chemicals found within leaf litter and seed oils have allelopathic effects on germination. Lettuce seed germination assays were conducted to test the allelopathic potential of Apiaceae seeds. The effect of the individual components of the essential oils of the seeds were also assayed. The percent germination, root length, and root hair length were measured in each assay. The Apiaceae seeds: fennel, cumin, caraway, celery, dill, anise and coriander were found to inhibit germination of lettuce at various seed densities. Fennel and cumin seeds were shown to also inhibit root and root hair elongation respectively. In fennel seeds, fenchone is present in sufficient amount to alone inhibit germination and root elongation, but not root hair elongation of lettuce seedlings. Similarly in cumin seeds, cuminyl alcohol inhibited germination and root hair elongation, but not root elongation. Similar germination results were observed for the other Apiaceae species providing evidence that the Apiaceae family generally has allelochemicals present in seed oils which inhibit germination and root and root hair elongation of lettuce. Reduced root and root hair lengths increase the chance of desiccation in seedlings before establishment and delay growth as water uptake is required for seedling growth. These results provide further evidence that allelopathic relationships exist between these species.
Figure 1. Fennel seeds inhibit lettuce germination at high densities, but inhibit root elongation without inhibiting root hair elongation at low seed densities.
Figure 2. Anethole, the major component of fennel seed oil, does not inhibit lettuce germination or root elongation even at high doses but root hair elongation is inhibited at low doses. Anethole is not likely the allelochemical in fennel seeds.
Figure 3. Fenchone, the second most abundant component of fennel seed oil, inhibits lettuce germination at high doses, and inhibits root elongation without inhibiting root hair elongation at low doses. Fenchone is the most-likely allelochemical in fennel seeds.
Figure 4. Cumin seeds inhibit lettuce germination at high densities but, inhibit root hair elongation on normal length roots at low seed densities.
Figure 5. Cuminaldehyde, the major component of cumin seed oil, inhibits seed germination at high doses, but shows normal root hair elongation on normal length roots at low doses. Cuminaldehyde is not likely the allelochemical in cumin seeds.
Figure 6. Cuminyl alcohol, the second-most abundant component of cumin seed oil, inhibits lettuce germination at high doses, and inhibits root hair elongation on normal length roots at low doses. Cuminyl alcohol is the most-likely allelochemical in cumin seeds.
Table 1.The effects of various Apiaceae and their essential oil components. Each was observed for inhibition of lettuce seed germination (G), root elongation (R), and root hair elongation (H). Lower case means mild, proportional.
(Foeniculum vulgare) GR
(Cuminum cyminum) GH
(Pimpinella anisum) R
cuminyl alcohol GH
(Carum carvi) G
(Coriandrum sativum) rh
(Anethum graveolens) G
(Apium graveolens) G
|Note: This poster was presented at the 1998 ßßß (Biological Honor Society) Northeast District 1 Convention at Worcester, MA by Steven Lamoureux, an undergraduate member of the society. His presentation was awarded first prize; the John C. Johson award plaque is displayed in the ECSU biology department and Steven received a certificate and a $750 travel award to attend the National Convention in San Diego this summer to present his work again.|
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