Evolution of the Secondary Metabolites in Invasive Plant Species Chromolaena odorata for the Defense and Allelopathic Functions

Abstract

Chromolaena odorata (L.) R.M. King & H. Robinson is native to tropical America, and has naturalized in many other countries in tropical Asia, Austria, and West Africa. The species often forms dense thickets and reduces the native species diversity and population in the invasive ranges. The species is also considered as a noxious weed in agriculture fields, and listed in the 100 of the world’s worst invasive alien species. The characteristics of its life-history such as the seed production rate, growth pattern, and adaptative ability to the environmental conditions may contribute to the invasiveness of the species. Possible evidence of the defense capacity against the natural enemy, and the allelopathic potential against the competitive plant species for C. odorata has been accumulated in the literature over three decades. The extracts, residues, and/or rhizosphere soil of C. odorata increased the mortality of various insects and parasitic nematodes, and decreased their population. The extracts, residues, and/or rhizosphere soil of C. odorata also inhibited the germination and growth of several plant species including the indigenous plant species in the invasive ranges of C. odorata. Toxic substances, pyrrolizidine alkaloids were found in the leaves and flowers of C. odorata. These pyrrolizidine alkaloids may work as the defense agents against the natural enemies. Several potential allelochemicals such as flavonoids, phenolic acids, and terpenoids were also found in the plant extracts of C. odorata. Some of these compounds may work as allelopathic agents of C. odorata and inhibit the germination and growth of the competitive plant species. These characteristics of C. odorata for the defense function against their natural enemies such as insects and parasitic nematodes, and allelopathic potential against the competitive native plant species may contribute to the invasiveness and naturalization of C. odorata in the new habitats as invasive plant species. However, it is necessary to determine the concentration of these allelochemicals in the neighboring environment of C. odorata such as the rhizosphere soil since allelochemicals are able to work only when they are released into the neighboring environment. It is the first review article focusing on the defense function and allelopathy of C. odorata.

Invasive Mechanisms of One of the World’s Worst Alien Plant Species Mimosa pigra and Its Management

“…Allelopathy is the interaction between donor plants and their neighboring plants through certain secondary metabolites that are defined as allelochemicals [ 81 , 82 , 83 , 84 ]. The allelochemicals are released into the vicinity of the donor plants either by volatilization, rainfall leachates, root exudation and decomposition processes of donor plant residues, and they suppress the germination, growth and establishment of neighboring plants, as well as exhibiting mutualism with rhizobia and arbuscular mycorrhizal fungi [ 85 , 86 , 87 , 88 , 89 , 90 , 91 ]. Since allelochemicals are synthesized and stored in certain plant tissues until releasing into the vicinity of donor plants [ 81 , 82 , 83 , 84 ], several researchers determined the allelopathic activity in the residues of the leaves and extracts from different plant parts of M. pigra .…”

“…Total annual litterfall of M. pigra was estimated to be 758 g m 2 [ 98 ], and such a litterfall may be one of the sources of allelochemicals of the species. Allelochemicals of the invasive plant species suppressed the regeneration process of the native plant species in their invasive ranges [ 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 ]. Allelochemicals of M. pigra may also suppress the regeneration process of the native plant species through the inhibition of their germination and growth.…”

Isolation and identification of allelochemicals and their activities and functions

“…Allelochemicals suppress the germination, growth, and regeneration process of the receiver plant species. [4][5][6] Some allelochemicals such as cinnamic acid, benzoic acid, and their derivatives disturb cell membrane permeability, water balance, and stomatal functions, and suppress the enzyme activities involved in the photosynthesis, protein synthesis, respiration, and the metabolism of some secondary metabolites including plant hormones. [7][8][9] The disruption of the metabolism and cell functions by allelochemicals may cause the inhibition of the germination, growth, and regen-eration process of the receiver plant species.…”

“…In addition, the extracts and residues of several plant species have shown significant weed control ability as soil additives and mulch because of the allelochemicals. [3][4][5][6] We selected plant species through the following three-step evaluation process: 1) the selection of possible plant species that dominate in natural conditions, 2) investigate plant species in publications and websites, and 3) evaluate the allelopathic activity of the crude extracts of the plant species. After the selection, we extracted the plant species, separated the extracts through the bioassay-guided purification process: evaluate the allelopathic activity of all fractions obtained after each separation step, and apply most active fraction to the next separation step.…”

Ecological insights and environmental threats of invasive alien plant Chromolaena odorata: Prospects for sustainable management

“…The native range of weed extends from southern America to northern Argentina (Dube et al, 2021; Mandal & Joshi, 2014). Tracing the historical records revealed that C. odorata was first introduced in Asia (specifically noted in Indo‐Gangetic plains) before 1870 in Serampore Botanical Gardens at Calcutta from where it spread to Assam (North East India), followed by Myanmar, to Indonesia and eventually to Indo‐China border (Kato‐Noguchi & Kato, 2023; McFadyen & Skarratt, 1996). In South Africa, C. odorata was introduced along with the import of Gmelina arborea Roxb.…”