Potential Allelopathic Effect of Species of the Asteraceae Family and Its Use in Agriculture

*Ana Daniela Lopes, Maria Graciela Iecher Faria Nunes, João Paulo Francisco and Eveline Henrique dos Santos*

## **Abstract**

Some species are capable of producing substances that affect seed germination, stimulating, or retarding this process, and can also suppress the development of other plants, acting as an antagonistic plant. This can occur naturally, through the release of exudates, or through the action of essential oil, extracts obtained from different parts of the plant, or plant residues with potential allelopathic action. The aim of this chapter is to present the main plant genera of the Asteraceae family with potential phytotoxic or allelopathic activity, with a suppressive effect on the growth of herbicide-tolerant weeds. The genus defined were *Acmella*, *Artemisia*, and *Bidens*, highlighting the form of use—plant extract, essential oil, or plant residues. The Asteraceae family is considered a repository of species to be explored for allelopathy with several associated secondary metabolites such as terpenes, saponins, alkaloids, alkamides, cinnamic acid derivatives, and flavonoids. In addition to these, for the genus *Bidens*, the presence of the acetylenic compound phenylheptatriine (PHT) is considered an important allelochemical with potent allelopathic action. The presence of this compound is associated with the cytotoxic activity of representatives of this genus, which can be a source of prospecting for new molecules to be used as bioherbicides.

**Keywords:** allelopathy, allelochemicals, bioherbicides, metabolites, weeds

## **1. Introduction**

The term allelopathy has been referenced and conceptualized in different ways and from different perspectives. It can be understood as the ability of plants to interfere with other organisms in the environment [1]; as a process where chemical compounds are released into the environment by an organism and, once released into the environment, interact and can influence the growth and development of biological systems, including inhibition or stimulation effects [2, 3]. Older definitions, such as that of Hans Molisch in 1937, consider allelopathy as the direct or indirect result of the transfer of chemical substances from one plant to another [4]. Thus, in 1996, the International Allelopathy Society (IAS) defined allelopathy as the science that studies any process, essentially involving secondary metabolites produced by plants, algae,

bacteria, and fungi, that influence the growth and development of agriculture and biological systems, including positive (stimulation) or negative (inhibitory) effects [5, 6]. It can be seen that, despite the different definitions, these refer, in short, to the central role of secondary metabolites in allelopathy [1], which are involved in defining the characteristics of natural ecosystems and agroecosystems [7].

The compounds identified with potential allelopathic activity are known as allelochemicals and, since their discovery, research has been carried out with the objective of isolating and identifying the substances responsible for this phenomenon and grouping them [8]. Allelochemicals can range from simple hydrocarbons to complex compounds of high molecular weight and can be classified into 10 categories according to their structures and properties: (1) water-soluble organic acids, straight chain alcohols, aliphatic aldehydes, and ketones; (2) simple lactones; (3) long-chain fatty acids and polyacetylenes; (4) quinones (benzoquinone, anthraquinone, and quinone complex); (5) phenolics; (6) cinnamic acid and its derivatives; (7) coumarins; (8) flavonoids; (9) tannins; and (10) steroids and terpenoids (sesquiterpene lactones, diterpenes, and triterpenoids) [9].

The performance of bioassays makes it possible to identify the phytotoxicity of different species, explained by the delay in seed germination, inhibition of plant growth, or any adverse effect caused by specific substances (phytotoxins) or growth conditions [10]. Unlike herbicides, allelochemicals act at low, but constant concentrations, over a long period of time. This fact, associated with the increase in global demand for organic products in the last two decades [11], makes it urgent to invest in studies on the use of allelochemicals as natural pesticides, in order to promote more sustainable agriculture, minimize the effects of pesticides on the environment and human health [12]. Among the benefits associated with the use of allelopathic compounds for the development of new agrochemicals, the fact that most of them are biodegradable and less polluting than traditional pesticides is highlighted due to their shorter half-lives [13].

Allelochemicals can be found in different parts of the plant, including flowers, leaves, stems, roots, or fruits of different species [2, 14]. Secondary metabolites present in medicinal and weed plants have been reported as potent growth inhibitory agents, indicating that such plants act as a depot for allelopathic compounds [15]. Many of these species are representatives of the Asteraceae family, which is composed of approximately 1000 genera, comprising more than 25,000 species of flowering plants [16], representing the largest family among flowering plants in the world, with distribution on all continents, except for Antarctica [17, 18]. This family includes food crops such as lettuce (*Lactuca sativa* L.), endive (*Cichorium endivia* L.), edible safflower seeds (*Carthamus tinctorius* L.), and sunflower (*Helianthus annuus* L.), species used in oil production (Enclyclopaedia Britannica 2015), medicinal species like *Achillea millefolium* L. [19], *Vernonia* spp. [20], and *Matricaria chamomilla* L. [21]; and species used in the bioremoval of pollutants in urban areas, such as metals and xenobiotics (*Solidago*, *Tanacetum*, and *Rudbeckia*) [22, 23]. Several secondary metabolites are present in the Asteraceae family such as terpenes [24], including sesquiterpene lactones [25, 26], saponins [27], alkaloids [28], alkamides [29], cinnamic acid derivatives, and flavonoids [30].

In this sense, this review intends to highlight, as a target for the search for natural alternatives in crop protection, genera of the Asteraceae family that grow spontaneously in different environments [31], some of which are capable of influencing the development of other species by allelopathy. Therefore, three genera of plants belonging to the Asteraceae family with recognized allelopathic activity were selected: *DOI: http://dx.doi.org/10.5772/intechopen.108709 Potential Allelopathic Effect of Species of the Asteraceae Family and Its Use in Agriculture*

*Acmella*, *Artemisia*, and *Bidens*. *Artemisia* and *Bidens* along with *Ambrosia*, *Bellis*, *Helianthus*, and *Tagetes* are the main genera of the Asteraceae family with allelopathic or phytotoxic activity. Furthermore, the phytotoxic potential of *Acmella oleracea* was recently described, for the first time, against the weeds *Calopogonium mucunoides* and *Ipomoea purpurea* [8], confirming allelopathy of its extract.

*A. oleracea* (L.) R. K. Jansen (synonymies *Spilanthes oleracea* L., *S. oleracea* Jacq., and *Spilanthes Acmella* auct. Non (L.) Murr.) popularly known as "jambu" is a plant native to the regions of Asia and South America (especially in the northern region of Brazil), where it is widely used in regional cuisine [32–34]. It is commonly used in folk medicine with proven healing, antispasmodic, anti-inflammatory, antimalarial activity, in the treatment of rheumatism, as a tonic [35, 36], antioxidant, antinociceptive, anti-inflammatory, diuretic, and anesthetic [37]. It also has larvicidal [38], insecticidal [39], acaricide [40], and anthelmintic [41] effects. Acidic amino acids, triterpenes, stigmasterol, and alkaloids predominate in the phytochemical profile of *A. oleracea*, however, the biological activity seems to be related to the abundant presence of N-alkylamides, especially spilanthol [37, 42]. Studies on allelopathic activity and the metabolites involved, however, are still poorly explored, except for the work of [43] who evaluated the inhibition effect, phytotoxicity, and metabolites present in the aqueous methanolic extract of *A. oleracea* (L.) R. K. Jansen on the growth of *Lolium multiflorum* Lam. and *Echinochloa crus-galli* (L.) P. Beauv.

The genus *Artemisia* has more than 350 species and is considered a promising source of biologically active compounds with the potential to provide new herbicides and growth regulators. The different species that make up the genus have phytotoxic compounds for monocots, dicots, photosynthetic bacteria, and endomycorrhizal fungi [44], especially *Artemisia annua* L., which center of origin is Asia [45] but after domestication it began to be cultivated in different countries such as Austria, Brazil, Spain, the United States, France, Poland, and Romania [46]. A. *annua* stands out in the Asteraceae family both for the variety of natural products characterized (almost 600 in total, including around 50 amorphane and cadinane sesquiterpenes), and by the highly oxygenated nature of secondary metabolites of the terpenoid class [47]. There are several studies that report the allelopathic activity of artemisinin and its synthetic derivatives, which can act as inhibitors and promoters of complex signals in response to biotic and abiotic factors [48–52], from the aqueous extract, essential oil, or biomass. Plant of its own species (**Figure 1**).

*Bidens pilosa* L. is an annual plant native to tropical America and widely distributed in tropical and subtropical regions of the world. The genus has about 280 species and is widespread in both cultivated and uncultivated areas, being considered one of the most harmful weeds in agriculture, promoting crop losses in more than 40 countries [53]. *B. pilosa* shows rapid growth exhibiting allelopathic effect on various cultures [53–57]. It is also used as a medicinal plant, cover plant, and source of nectar for bees. Its roots, leaves, and seeds have antibacterial, antidysenteric, anti-inflammatory, antimalarial, antiseptic, anticancer, antipyretic, hepatoprotective, hypotensive, hypoglycemic, diuretic, and antidiabetic activity [58, 59].

Xuan and Khanh [60] systematized a literature review based on 218 literary sources reported over 40 years highlighting chemical constituents, nutraceuticals, ethnomedical, biological, and pharmacological uses, and the effects and toxicity of *B. pilosa*. In this survey, the authors reported that the main compounds (301 compounds) belong to the group of polyacetylenes, polyacetylene glycosides, flavonoids, flavone glycosides, aurones, chalcones, okanine glycosides, phenolic acids, terpenes, pheophytins, fatty acids, and phytosterols, the which were identified and isolated

**Figure 1.**

*Graphic summary referring to the main genera of plants of the Asteraceae family used how potential allelopathic in agriculture.*

from different parts of this plant and considered as bioactive compounds potentially responsible for the pharmacological action, biological and allelopathic properties of the species, which will be described in more detail below.

It is important to highlight, however, that most of the articles that suggest the allelopathic effect of the crude extract of a plant species do so through bioassays, useful tools for previous studies on the allelopathic potential of a species or compound, however, not suitable for sufficient to relate the results obtained in vitro, in the laboratory, with field conditions [3, 61, 62]. For this reason, results from bioassays developed under natural conditions were included in this review [63, 64]. Under these conditions, the biosynthesis of allelochemicals and their release can be influenced by temperature, luminosity, humidity, interaction with soil biota, and nutrient availability [3, 65, 66]; in addition to the fact that plants are evaluated at the initial stage of development, considered the most sensitive stage to allelochemical activity [67, 68].
