Abstract
Arbuscular mycorrhizal fungi (AMF) are obligatory biotrophics, which complicates the feasibility of producing inoculants. Thus, the discovery of substances capable of stimulating mycorrhizal colonization, as the isoflavone formononetin emerges as a promising alternative to explore the benefits of AMF native soil in extensive crops. The objective of this study was evaluate the application of the isoflavone formononetin (7-hydroxy-4'-methoxy isoflavone), fungicide application via seed in Cerrado soil in no-tillage system and fertilized with two doses of phosphorus in soybean under field and controlled conditions. In the field experiment treatments there were three levels of formononetin (0, 0.5 and 1.0 mg/seed Formononetin), in the absence and presence of fungicide (Carbendazim + Thiram commercial mix) applied to seeds and two doses of phosphorus (100 % and 33% of the recommended fertilization). The study was conducted until the maturation of soybeans. The greenhouse conditions experiment was implemented with the same treatments used in the field study and the flowering stage of the soybean plant was simulated water stress for 10 days, returning to normal irrigation to harvest the grain. Applying formononetin stimulated increased mycorrhizal colonization, number of nodules, vegetative growth and soybean production in the greenhouse and in the field and contributes to attenuate the negative effect of the fungicide Carbendazim + Thiram in soybean reflecting increased soybean production and adequate supply of soil phosphorus and high density of propagules of natives AMF contributed to reduce the benefits of stimulating mycorrhizal (formononetin) in the studied soil.
Highlights
The arbuscular mycorrhizal fungi (AMFs) are obligatory biotrophics, belonging to the Glomeromycota phylum (SCHÜSSLER et al, 2001), which colonize the root of the majority of the vascular plants, forming mutualistic symbiosis, that provides many benefits and increased production of the colonized plants (MOREIRA; SIQUEIRA, 2006)
The formononetin increased mycorrhizal colonization by mycorrhizal fungi (AMF) natives contributed to increases of 4% in plant height, 14% in the number of pods per plant and 11 % in grain yield (Table 1). This stimulating effect agrees with several studies, which showed that formononetin application acts to accelerate the germination of spores of Arbuscular mycorrhizal fungi (AMF) colonization and increase in soybean roots (BAPTISTA; SIQUEIRA, 1994; PAULA; SIQUEIRA, 1990; SILVAJUNIOR; SIQUEIRA, 1997), due to these benefits for the plant, the fomononetina is already released in several countries (PHC, 2014)
Similar effect was reported by Siqueira et al (1991a) for formononetin in protecting plants against the residual effect of herbicides, confirming the results found in this study
Summary
The arbuscular mycorrhizal fungi (AMFs) are obligatory biotrophics, belonging to the Glomeromycota phylum (SCHÜSSLER et al, 2001), which colonize the root of the majority of the vascular plants, forming mutualistic symbiosis, that provides many benefits and increased production of the colonized plants (MOREIRA; SIQUEIRA, 2006). This symbiosis between AMF and plant does not replace the phosphorus fertilization, it increases the efficiency of plant uptake of soil phosphorus in natural or added conditions, which makes it extremely important for Cerrado soils (CORDEIRO et al, 2005; FERREIRA et al, 2012). The use of these fungi in annual crops like soybean, is limited due he availability and technical and economic viability of AMF inoculum production on a large scale, once these fungi are obligatory biotrophics (MOREIRA; SIQUEIRA, 2006). The discovery of substances able to stimulate mycorrhizal colonization, like the isoflavonoid formononetin (NAIR et al, 1991), appears as a promising alternative to exploit the benefits of native AMF in extensive crops system (SIQUEIRA et al, 2002)
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