Search Results (2)

The allelopathic plant Rhus typhina (Rt) has a shallowly distributed root system with a high density of secretory canals, which may allow it to exhibit indirect allelopathic effects through the soil on an understory turf species in a plantation. However, how these effects occur is still not well understood. For this study, the soil from the root zone of Rt was extracted via distilled water, and extracts at different concentrations (25, 50, and 100 g L⁻¹) were used to treat six commonly planted turfgrass species, including Medicago sativa (Ms), Lolium perenne (Lp), Trifolium repens (Tr), Medicago falcata (Mf), Festuca arundinacea (Fa) and Coronilla varia (Cv), during a continuous germination–seedling culture experiment via the sand culture method. The germination, physiological, and growth indicators of the turfgrass seedlings were analyzed. The allelopathic effects of the soil extract at different concentrations on the six receivers were evaluated to provide a scientific basis for managing plantations with multilayer structures. The results indicated that, in general, the extracts of the soil from the root zone of Rt inhibited the germination and seedling growth performance characteristics of the mentioned turfgrasses; the inhibitory effects on Ms, Lp, and Mf increased with increasing concentrations of the Rt soil extracts, whereas those on Fa tended to decrease. In addition, the inhibitory effect on Tr obviously weakened at 50 g·L⁻¹ relative to that at 25 g·L⁻¹, whereas it became more obvious at 100 g·L⁻¹; however, it exhibited the opposite trend for Cv. Generally, Mf and Cv were more sensitive to Rt allelochemicals at relatively low concentrations, and these species should be avoided when planting in Rt plantations at low densities. In contrast, Lp and Tr were more sensitive than those at relatively high concentrations and should be avoided when planting in Rt plantations at high densities. Full article

Ageratum conyzoides L. is native to Tropical America, and it has naturalized in many other tropical, subtropical, and temperate countries in South America, Central and Southern Africa, South and East Asia, Eastern Austria, and Europe. The population of the species has increased dramatically as an invasive alien species, and it causes significant problems in agriculture and natural ecosystems. The life history traits of Ageratum conyzoides, such as its short life cycle, early reproductive maturity, prolific seed production, and high adaptive ability to various environmental conditions, may contribute to its naturalization and increasing population. Possible evidence of the molecules involved in the defense of Ageratum conyzoides against its natural enemies, such as herbivore insects and fungal pathogens, and the allelochemicals involved in its competitive ability against neighboring plant species has been accumulated in the literature. The volatiles, essential oils, extracts, residues, and/or rhizosphere soil of Ageratum conyzoides show insecticidal, fungicidal, nematocidal, and allelopathic activity. The pyrrolizidine alkaloids lycopsamine and echinatine, found in the species, are highly toxic and show insecticidal activity. Benzopyran derivatives precocenes I and II show inhibitory activity against insect juvenile hormone biosynthesis and trichothecene mycotoxin biosynthesis. A mixture of volatiles emitted from Ageratum conyzoides, such as β-caryophyllene, β-bisabolene, and β-farnesene, may work as herbivore-induced plant volatiles, which are involved in the indirect defense function against herbivore insects. Flavonoids, such as nobiletin, eupalestin, 5′-methoxynobiletin, 5,6,7,3′,4′,5′-hexamethoxyflavone, and 5,6,8,3,4′,5′-hexamethoxyflavone, show inhibitory activity against the spore germination of pathogenic fungi. The benzoic acid and cinnamic acid derivatives found in the species, such as protocatechuic acid, gallic acid, p-coumaric acid, p-hydroxybenzoic acid, and ferulic acid, may act as allelopathic agents, causing the germination and growth inhibition of competitive plant species. These molecules produced by Ageratum conyzoides may act as defense molecules against its natural enemies and as allelochemicals against neighboring plant species, and they may contribute to the naturalization of the increasing population of Ageratum conyzoides in new habitats as an invasive plant species. This article presents the first review focusing on the defense function and allelopathy of Ageratum conyzoides. Full article