Formononetin associated with phosphorus influences soybean symbiosis with mycorrhizal fungi and Bradyrhizobium

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 P₂O₅ 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 P₂O₅, formononetin increased soybean productivity to values similar to those observed when 120 kg ha^-1 de P₂O₅, was applied. At doses above 50 g ha^-1, formononetin applied to the seeds can reduce the need of P fertilization by 50%.