Biologically active secondary metabolites in white clover (Trifolium repens L.) – a review focusing on contents in the plant, plant–pest interactions and transformation

Abstract

To exploit biologically active compounds from white clover (Trifolium repens L.) for suppressing weeds and soil-borne diseases, either as isolated products (biopesticides) or through cultivars with enhanced production of these compounds, the biologically active compounds must be identified, plant content measured, and their fate in soil known. The present review summarizes the published knowledge needed for such exploitation; providing essential information on structure and concentration of flavonols, flavones, condensed tannins, isoflavones, isoflavanones, pterocarpans, coumestans, cyanogenic glucosides, and saponins in healthy and stressed white clover plants. Various stresses and particular cultivars affect the concentrations of several of the compounds. Information on biological effects and the degradation/transformation of these compounds in plants or by microorganisms is available. There is no information on the degradation pathway in soil, the mechanisms of exudation and leaching of compounds from plants, and soil sorption properties of the compounds. The clover soil fatigue problem is increasing in grasslands and causes problems especially in organic farming. Research efforts focused on biological elements of clover soil fatigue have not explained it, and the influence of secondary metabolites has not been investigated. There are few investigations into the interaction between beneficial fungi/fungal-diseases and the occurrence of biologically active secondary metabolites in white clover plants. Such studies are critical to better understand beneficial fungi and pathogens.

Fate in Soil of Flavonoids Released from White Clover (Trifolium repensL.)

“…The isoflavonoids and flavones probably have other biological functions than the flavonols, since it has been shown that the concentrations of the isoflavones formononetin and daidzein in roots of white clover increased in response to infection with the root pathogen Pythium ultimum [15]. Previous reports of total isoflavone concentrations in white clover plants ranged between 0.09 and 1.0 mg/g dry weight [12,[16][17][18][19], with isoflavonoids predominantly occurring as glycoside conjugates [20,21], and formononetin glucoside-(di)-malonate(s) and medicarpin-glucosidemalonate being the major isoflavonoids in white clover plants [19,21]. In our study we did not quantify sugar conjugates of formononetin or medicarpin, but the concentrations of the aglycones of those two compounds were high compared to previous reports.…”

“…Legumes that are used as cover crops or incorporated into the soil may also function as a supplement or even replacement for pesticides. Several studies have reported suppressive effects of white clover on weed pressure and diseases or unexplained failure of oversown grasses in swards dominated by clover [1][2][3][4][5][6][7][8][9][10][11][12]. Secondary metabolites have been suspected of causing these effects, and basic knowledge on the release, active or passive, of biologically active secondary metabolites from white clover is therefore much needed.…”

Allelopathic effect of the invasive Acacia dealbata Link (Fabaceae) on two native plant species in south-central Chile

“…It has been shown that members of Acacia-sensu lato contain amines, simple cyanogenic glycosides, cyclitols, essential oils, diterpenes, fatty acids in oilseeds, fluoroacetate, gums, non-protein amino acids, triterpenes, phytosterols, saponins, flavonoids and tannins; however, the identification of these compounds results from the study of a small number of species within this genus (Seigler 2003). Some of the above secondary metabolites have been associated with phytotoxic or inhibitory activity, for example alkaloids (Elakovich & Yang 1996, Hornoy et al 2012, Goyal 2013, cyanogenic glycosides (Carlsen & Fomsgaard 2008, Ambika 2013, terpenes (Ens et al 2009, Macias et al 2010, flavonoids (Carlsen & Fomsgaard 2008, Ambica 2013 and tannins (Carlsen & Fomsgaard 2008). Acacia dealbata Link (silver wattle, aromo) one of the most widely distributed species of the genus Acacia.…”

Pesticides of Botanical Origin: a Promising Tool in Plant Protection

“…chewing insects) the cyanogenic glucosides are released from the vacuoles and hydrolyzed by specific b-glucosidases to yield glucose, a ketone or an aldehyde and toxic HCN. This process is known as cyanogenesis and serves to facilitate a rapid HCN release (Figure 2) that suppress insects, fungus, nematodes and weeds (Zagrobelny et al, 2004;Morant et al, 2007;Bjarnholt et al, 2008;Carlsen & Fomsgaard, 2008). Cyanogenic glycosides, through the action of cyanide, prevent oxygen utilization by the inhibition of cytochrome oxidase (Majak, 1992).…”

“…Phenolics are toxic to insects, fungi, bacteria, nematodes and weeds (Koul, 2008;Carlsen & Fomsgaard, 2008;Simmonds & Stevenson, 2001;Popa et al, 2008;Wu et al, 2001;Simmonds, 2003;Chitwood, 2002). Flavonoids, a major class of phenolic compounds, are distributed widely in vascular plants and Bryophytes, and ca.…”