Flavonoids in roots of white clover: interaction of arbuscular mycorrhizal fungi and a pathogenic fungus

Abstract

The effects of two arbuscular mycorrhizal fungi (AMF) (Glomus mosseae and G. claroideum) and a pathogenic fungus (Pythium ultimum) on the production of eight flavonoids in roots of two white clover (Trifolium repens L.) cultivars were evaluated. Quantification of AM and pathogenic fungi in the roots showed that the AM symbiosis significantly reduced P. ultimum biomass and in some cases prevented infection. The flavonoid productions in clover roots varied depending on the presence of beneficial and/or pathogenic fungi, fungal isolate or plant cultivar. Only plants colonized with G. claroideum showed detectable concentrations of either coumestrol or kaempferol (cultivar-dependant). In addition, inoculation with G. claroideum resulted in significantly higher concentrations of coumestrol in cv. Sonja and medicarpin in cv. Milo. A low production of coumestrol and kaempferol in mycorrhizal plants may be G. mosseae-specific. Only the concentrations of formononetin and daidzein increased in clover roots in response to infection with P. ultimum. These flavonoids are supposedly stress metabolites, synthesized or produced from glycosides in response to pathogen infection. However, the presence of one or both AMF significantly lowered the formononetin and daidzein concentrations, and overruled the inductive effect of P. ultimum. Therefore the antagonistic action of AM against the pathogen must take place through another mechanism.

Plant-borne flavonoids released into the rhizosphere: impact on soil bio-activities related to plant nutrition. A review

“…Inoculation of a plant with either a phytopathogenic fungus or a putative mycorrhizal partner induces changes in the pattern of secreted flavonoids (Carlsen et al 2008), suggesting that flavonoids are also involved as signal molecules for the plant-fungal interactions. As an example of these interactions, we shall discuss the effects of plant-secreted flavonoids on mycorrhizal, phytopathogenic, and saprophytic fungal partners.…”

Silicon-Induced Changes in Antifungal Phenolic Acids, Flavonoids, and Key Phenylpropanoid Pathway Genes during the Interaction between Miniature Roses and the Biotrophic Pathogen Podosphaera pannosa

“…However, the involvement of flavonoids in plant defense depends on the species (Dixon and Paiva, 1995;Carlsen et al, 2008).…”

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].…”