Allelopathic Substances of Osmanthus spp. for Developing Sustainable Agriculture

Abstract

Osmanthus fragrans Lour. has been cultivated for more than 2500 years because of the fragrance and color of the flowers. The flowers and roots have been used in tea, liquors, foods, and traditional Chinese medicine. The species contains more than 180 compounds including terpenoids, phenylpropanoids, polyphenols, flavonoids, and sterols. However, there has been limited information available on the allelopathic properties and allelopathic substances of O. fragrans. We investigated the allelopathy and allelopathic substances of O. fragrans and Osmanthus heterophyllus (G.Don) P.S. Green, as well as Osmanthus × fortunei Carrière, which is the hybrid species between O. fragrans and O. heterophyllus. The leaf extracts of O. fragrans, O. heterophyllus, and O. × fortunei suppressed the growth of cress (Lepidium sativum L.), alfalfa (Medicago sativa L.), Lolium multiflorum Lam., and Vulpia myuros (L.) C.C.Gmel with the extract concentration dependently. The extract of the hybrid species O. × fortune was the most active among the extracts. The main allelopathic substances of O. × fortunei and O. fragrans were isolated and identified as (+)-pinoresinol and 10-acetoxyligustroside, respectively. (+)-Pinoresinol was also found in the fallen leaves of O. × fortunei. Both compounds showed an allelopathic activity on the growth of cress and L. multiflorum. On the other hand, several allelopathic substances including (+)-pinoresinol may be involved in the allelopathy of O. heterophyllus. O. fragrans, O. heterophyllus, and O. × fortunei are evergreen trees. but their senescent leaves fall and cover the soil under the trees. It is possible that those allelopathic substances are liberated through the decomposition process of the leaves into their rhizosphere soil, and that they accumulate in the soil and provide a competitive advantage to the species through the inhibition of the growth of the neighboring competing plants. Therefore, the leaves of these Osmanthus species are allelopathic and potentially useful for weed management options in some agriculture settings to reduce commercial herbicide dependency for the developing sustainable agriculture systems.

Keywords: (+)-pinoresinol; 10-acetoxyligustroside; Osmanthus; allelochemical; decomposition; fallen leaf; growth inhibition.

Figure 1

The leaves of O. fragrans, O. × fortunei, and O. heterophyllus.

Figure 2

The accumulation of the fallen leaves on the soil under the tree of O. × fortune.

Figure 3

Effects of the extracts of O. fragrans leaves on the growth of the hypocotyls and roots of cress and alfalfa, and the growth of the coleoptiles and roots of L. multiflorum and V. myuros. Concentration (mg leaf equivalent extract/mL) indicates the concentration of the tested sample corresponding to the extracts obtained from 1, 3, 10, 30, 100, 300, and 1000 mg leaves per mL. Different letters on the symbols in the same panels indicate significant differences (Tukey’s HSD test, p ≤ 0.05).

Figure 4

Effects of the extracts of O. heterophyllus leaves on the growth of the hypocotyls and roots of cress and alfalfa, and the growth of the coleoptiles and roots of L. multiflorum and V. myuros. Concentration (mg leaf equivalent extract/mL) indicates the concentration of the tested sample corresponding to the extracts obtained from 1, 3, 10, 30, 100, 300, and 1000 mg leaves per mL. Different letters on the symbols in the same panels indicate significant differences (Tukey’s HSD test, p ≤ 0.05).

Figure 5

Effects of the extracts of O. × fortunei leaves on the growth of the hypocotyls and roots of cress and alfalfa, and the growth of the coleoptiles and roots of L. multiflorum and V. myuros. Concentration (mg leaf equivalent extract/mL) indicates the concentration of tested sample corresponding to the extracts obtained from 1, 3, 10, 30, 100, 300, and 1000 mg leaves per mL. Different letters on the symbols in the same panels indicate significant differences (Tukey’s HSD test, p ≤ 0.05).

Figure 6

Chemical structure of (+)-pinoresinol.

Figure 7

Effects of (+)-pinoresinol on the hypocotyl/coleoptile and root growth of cress and L. multiflorum. Means ± SE from three independent experiments with 10 seedlings for each determination are shown. Different letters on the symbols in the same panels indicate significant differences (Tukey’s HSD test, p ≤ 0.05).

Figure 8

Chemical structure of 10-acetoxyligustroside.

Figure 9

Effects of 10-acetoxyligustroside on the hypocotyl/coleoptile and root growth of cress and L. multiflorum. Means ± SE from three independent experiments with 10 seedlings for each determination are shown. Different letters on the symbols in the same panels indicate significant differences (Tukey’s HSD test, p ≤ 0.05).