VA-mycorrhizae and mycorrhiza stimulating isoflavonoid compounds reduce plant herbicide injury

Abstract

Imazaquin, imazethapyr and pendimethalin showed high toxicity to sorghum plants grown in a greenhouse soil mix. However, mycorrhizal sorghum plants were less affected by herbicide toxicity than non-mycorrhizal ones, at low to moderate herbicide concentrations. VAM herbicide safening effects were more evident on imazaquin-treated plants, than for those treated with the other two herbicides. Applications of imazethapyr and pendimethalin at the two highest concentrations, but not imazaquin, reduced VAM colonization rates in sorghum. Applications of the VAM stimulating isoflavonoids, biochanin A and formononetin, at 5 ppm solutions to a field soil sample containing toxic levels of imazaquin (13 ppb) and indigenous VAM fungi, reduced herbicide-induced injury in corn and sorghum under growth chamber conditions. The benefits of isoflavonoids were reduced when additional propagules of Glomus intraradix were added into field-soil samples, and were eliminated when VAM fungi were inactivated by autoclaving. This indicates that herbicide safening effects of biochanin A, and formononetin are VAM-mediated and also suggests the potential use of these isoflavonoids as herbicide safeners.

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

“…The mechanisms by which flavonoid compounds stimulate fungal growth (Nair et al, 1991;Gianinazzi-Pearson et al, 1989) and root colonization (as reported here) cannot be determined from our experiments. As indicated by others (Adesanya, O'Neill & Roberts, 1986), the effects of these compounds on fungi may result from their effects on membrane permeability, enzyme activity or DNA transcription.…”

“…Inoculations with VAM fungi can result in accumulation of isoflavonoid compounds in legumes (Morandi, Bailey, & Gianinazzi-Pearson, 1984;Morandi, 1989); but, the possible effects of these compounds on VAM colonization and plant growth have been overlooked. Formononetin and biochanin A, previously isolated and identified from clover roots (Nair et al, 1991), exhibited the highest biological activity for stimulating VA mycorrhiza formation, whereas the other flavonoids tested, including the isoflavonoid genestein, were inactive when applied at solution concentrations of 5mgr'. Although formononetin and biochanin A have been found to exhibit low antifungal activity against other soil fungi (Debnam & Smith, 1976), their VAM stimulating effects are rather unexpected since these compounds are considered as phytoalexins (Van Etten, 1976) and also as allelochemicals in clover at concentrations of 100 mg r^ or higher (Tamura et al 1969).…”

“…These compounds can stimulate fungal growth directly or remove fungal self-inhibition, if they exist in VA mycorrhizal fungi. Formononetin and biochanin A, both identified in clover roots (Nair et al, 1991), are produced in suspensioncultured cells as normal cell metabilites (Koster, Strack & Barz, 1983;Kebmann, Daniel and Barz, 1988) and were recently found in VA mycorrhizal growth-stimulating cells of Pueraria (Nair, Siqueira & Paula, unpublished). As plant signals these isoflavonoids may stimulate the free living fungus to use its endogenous reserves (Becard & Piche, 1989).…”

Fitorremediação de solos contaminados com herbicidas

“…No entanto, tem-se observado a ocorrência de fitotoxicidade em culturas sensíveis (carryover) plantadas após a utilização desses herbicidas, cujo efeito residual varia de alguns meses até três anos ou mais. Esse fenômeno tem sido observado para os herbicidas atrazine e imazaquin (Siqueira et al, 1991), além de outros, como tebuthiuron, fomesafen e trifloxysulfuronmetyl. Nessa situação, torna-se possível e recomendável o emprego de espécies vegetais na descontaminação dos solos.…”

Fitorremediação do herbicida trifloxysulfuron sodium

“…Além disso, produtos que apresentam efeito residual longo -que pode variar de alguns meses até três anos ou mais -provocam fitotoxicidade em culturas sensíveis (carryover) plantadas após a utilização desses herbicidas, como observado para atrazine e imazaquin por Siqueira et al (1991).…”