Abstract
Arbuscular mycorrhizal fungi play an important role on nutrient supply to plants, specially P. However, the availability of inoculants for large-scale usage in agriculture is still limited because these organisms are obligatory symbionts. The use of symbiosis stimulants such as flavonoids can be an alternative to improve the beneficial effects of mycorrhiza for plant nutrition. The aim of this study was to evaluate the effect of the isoflavonoid biostimulant formononetin (7-hydroxy, 4’-methoxy isoflavone) in combination with three levels of phosphorus fertilization on mycorrhizal colonization, nodulation, and productivity of soybean, under field conditions. A 3 x 4 factorial scheme (levels of P: 0, 60 and 120 kg ha -1 P 2 O 5 and doses of formononetin: 0, 25, 50 and 100 g ha -1 ) was used with five replicates. The following parameters were quantified at full bloom: plant height, shoot dry weight, nodule number, nodule dry weight, mycorrhizal colonization, and shoot N and P concentrations. Productivity was also evaluated at the end of the crop cycle. Formononetin stimulated mycorrhizal colonization at lower levels of P (0 and 60 kg ha -1 ), with colonization increasing from 56 to 64%. When applied with 60 kg ha -1 P 2 O 5 , formononetin increased soybean productivity to values similar to those observed when 120 kg ha -1 de P 2 O 5 , was applied. At doses above 50 g ha -1 , formononetin applied to the seeds can reduce the need of P fertilization by 50%.
Highlights
Soybean (Glycine max (L.) Merrill) is an important source of protein in the human and animal food chains
Because soybean can form symbiosis with N2-fixing bacteria belonging to the genus Bradyrhizobium, the plant demand for N may be completely supplied by biological nitrogen fixation (MOREIRA; SIQUEIRA, 2006)
The need for P fertilization can be reduced by arbuscular mycorrhizal fungi (AMF), which improve P uptake by their host plants due to the establishment of a hyphal network that increases the volume of soil exploited by the root (PARNISKE, 2008; STÜRMER; SIQUEIRA, 2013)
Summary
Soybean (Glycine max (L.) Merrill) is an important source of protein in the human and animal food chains This crop has high economic and social importance in Brazil, the greatest soybean producer worldwide. Soybean plants form symbiotic associations with both N2-fixing bacteria and AMF, with the interaction among the three organisms resulting in a tripartite symbiosis (ANTUNES et al, 2006). Synergetic effects of this tripartite symbiosis have been observed, mainly in conditions of low levels of P and N (MOREIRA et al, 2010; WANG et al, 2011). In soybean Cordeiro et al (2015) reported that formononetin increased mycorrhizal colonization, nodulation, plant growth, and productivity in both greenhouse and field conditions, attenuating the negative effects of fungicides
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