Stimulation of vesicular‐arbuscular mycorrhiza formation and growth of white clover by flavonoid compounds

summary The effects of flavonoid compounds on VA mycorrhiza root colonization and growth of white clover ( Trifolium repens L.) plants under growth chamber conditions are reported. The isoflavonoids, formononetin and biochanin A, previously identified from clover roots, stimulated colonization and growth of clover, while several other flavonoid compounds were inactive when tested at concentrations of 5 mg 1 −1 . The flavone, chrysin, when applied at concentrations higher than those tested for formononetin and biochanin A, also increased root colonization and plant growth. The stimulatory effects of the isoflavonoids on plant growth were mediated by VA mycorrhizal fungi and were dependent on concentration, period of growth and soil spore density. Maximum responses were found when 5 mg 1 −1 solutions were applied to soil containing 2 to 4 VA mycorrhiza spores g −1 of soil. These results may provide insights on the molecular mechanisms of host‐fungus interaction and for the development of technology to exploit the potential of the indigenous VA mycorrhizal fungi in field soil.