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

Abstract

SUMMARYThe effects of flavonoid compounds on VA mycorrhiza root colonization and growth of w-hite 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 growtb of clover, while several other flavonoid compounds were inactive when tested at concentrations of 5 mg 1"', The flavone, chr\'sin, wben applied 3t concentrations higher than those tested for formononetin and biochanin A, also increased root colonization and plant growth. The stimulatory effects of the isoflavonoids on p\ant growth were mediated by VA mycorrhiza) fungi and were dependent on concentration, period of growth and soil spore density. Maximum responses were found when 5 mg 1"' solutions were applied to soi! containing 2 to 4 VA mycorrhiza spores g"^ of soil. Tbese results may provide insights on the molecular mechanisms of bost-fungus interaction and for the development of technology to exploit the potential of the indigenous VA mycorrhizai fungi in field soil.

Efeito da formononetina (7 hidroxi, 4'metoxi isoflavona) na colonização micorrízica e crescimento do milho em solo contendo excesso de metais pesados

“…No nível mais alto de contaminação, a colonização foi reduzida em 75% em relação ao solo controle sem contaminantes, mesmo na presença de formononetina. No solo não contaminado, a aplicação dessa substância aumentou em quase 50% a colonização das raízes, confirmando os resultados de vários outros estudos com estes flavonóides em milho (Siqueira et al, 1991b;Silva Jr. & Siqueira, 1997). No entanto, esses incrementos diminuíram com a elevação da proporção de solo contaminado, sendo inexistente a 10%.…”

“…Como discutido em trabalhos já citados, a colonização micorrízica pode amenizar o estresse da fitotoxidez de metais e, à semelhança do que tem sido demonstrado para estresse induzido por resíduo de herbicida no solo (Siqueira et al, 1991b), a aplicação dessa substância pode favorecer o crescimento de plantas em solo com excesso de metais. Isto foi objeto do presente estudo, que utilizou o milho como planta-teste.…”

Specific flavonoids as interconnecting signals in the tripartite symbiosis formed by arbuscular mycorrhizal fungi, Bradyrhizobium japonicum (Kirchner) Jordan and soybean (Glycine max (L.) Merr.)

“…Mycorrhizal fungi may have evolved to use the most abundant flavonoid to induce hyphal branching and stimulate colonization. Other studies either failed to identify an effect of genistein on hyphal growth (Baptista and Siqueira, 1994) and root colonization (Siqueira et al, 1991) or have even indicated an inhibition of the fungal development (Chabot et al, 1992).…”

Arbuscular mycorrhizal fungi and mycorrhizal stimulant affect dry matter and nutrient accumulation in bean and soybean plants1

“…In the early 1990s, Nair et al (1991) and Siqueira et al (1991) found that some chemical substances were able to act as biochemical signals and as mycorrhizal colonization stimulants of native arbuscular mycorrhizal fungi, such as isoflavonoid formononetin . These stimulants are alternatives to maximize benefits in the nutritional improvement of plants and in the reduction of biotic and abiotic stresses.…”