Abstract
ABSTRACT Seed treatment with fungicides is an important practice for the control of phytopathogens in peanut crops. However, these products can harm rhizobacteria (Bradyrhizobium) and inhibit processes such as biological nitrogen fixation. This study aimed to verify the effects of the treatment of peanut seeds cv. BR1 inoculated with Bradyrhizobium spp. with fungicides. The experiment was conducted in a greenhouse, using two combinations of fungicides [C1: carboxin (200 g L-1) + tiram (200 g L-1); C2: pyraclostrobin (25 g L-1) + thiophanate methyl (225 g L-1) + fipronil (250 g L-1)] and one control without fungicide; two inoculants based on Bradyrhizobium spp. (SEMIA 6144 and ESA 123) and one control with a nitrogen chemical source (ammonium nitrate). The experimental design was completely randomized, in a 3 (2 with fungicide and 1 without fungicide) x 4 (2 inoculations based on rhizobia, 1 N mineral source and 1 without N) x 2 (1 or 2 inoculants applications) factorial scheme, with 5 replications. The root and shoot dry mass, plant height, nodulation and leaf nitrogen accumulation were evaluated. The application of both combinations reduced the number of nodules on plant roots, mainly for C1. The vegetative growth and nitrogen in the leaves were affected by C1, whereas, for C2, there were increments higher than for the control without fungicides. ESA 123 was more tolerant to the effects of fungicides on nodulation. Regarding the number of inoculations, there was an increase in the nitrogen rate with two inoculations. C2, despite affecting the nodulation, was less toxic to the inoculants SEMIA 6144 and ESA 123.
Highlights
Worldwide, 40-66 million tons of nitrogen (N2) are fixed annually by plants of the Fabaceae family, which constitute almost half of the N used in agriculture (Egamberdieva et al 2017)
This study aimed to evaluate the compatibility and effects resulting from the treatment of peanut (A. hypogaea L.) seeds with fungicides on nodulation with bacteria of the Bradyrhizobium spp. genus on plant development and leaf nitrogen content
Two inoculants based on Bradyrhizobium spp. (ESA 123 and SEMIA 6144) and two combinations of fungicides of the systemic and contact chemical defensive class [C1: carboxin (200 g L-1) + tiram (200 g L-1); C2: pyraclostrobin (25 g L-1) + thiophanate methyl (225 g L-1) + fipronil (250 g L-1)] were used at the dose recommended by the manufacturer (300 mL of commercial product/100 kg of seeds)
Summary
40-66 million tons of nitrogen (N2) are fixed annually by plants of the Fabaceae family (legumes), which constitute almost half of the N used in agriculture (Egamberdieva et al 2017). The biological nitrogen fixation brings economic and environmental benefits to nitrogen deficient soils. This process makes it possible to replace nitrogen fertilizers, which have high prices. Rhizobia have the nitrogenase enzyme, capable of breaking the triple bond of nitrogen (N≡N) in the atmosphere, making it assimilable to the plant as ammonia nitrogen. The plant offers protection to microorganisms within its roots and organic compounds from photosynthesis (Fernandes Junior & Reis 2008, Geurts et al 2016)
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