Bacillus subtilis associado a Trichoderma asperellum e seus efeitos na morfometria, uso dos nutrientes e fisiologia de capim Marandu.

Abstract

Marandu grass Urochloa (Syn Brachiaria) brizantha is a forage of high importance and has large areas in Brazil. The objective of this work was to make available the effects of biostimulants in the efficient use of nutrients, improve the photosynthetic apparatus and provide more significant plant growth. The experiment was carried out in a greenhouse. Three experiments were carried out independently, evaluating the reductions of alcohol (Experiment 1), phosphorus (Experiment 2), and potassium (Experiment 3), inoculated or not. The experimental design was completely randomized in a 5 x 3 factorial scheme with five replications. The evaluated factors were: Mineral fertilizer rate: 0, 25, 50, 75, and 100% of the recommended dose and inoculation with growth-promoting microorganisms: non-inoculated, inoculated with Bacillus subtilis (UFRA-92) and co-inoculated with Trichoderma asperellum composed of the isolates (UFRA-06, UFRA-09, UFRA-12, and UFRA-52) and Bacillus subtilis (MIX). Inoculation was done via irrigation and 35 days after emergence and biometric parameters were measured: plant height, root length, leaf, and root dry mass and were calculated: leaf appearance rate, leaf elongation rate, leaf area . The leaves were collected and remained for the composition of bacteria, phosphorus, and potassium. Nutrient use efficiency was calculated from agronomic efficiency, regulatory efficiency, recovery efficiency, and nutrient response efficiency. The best treatments and doses of nitrogen, phosphorus, and potassium were found in the first test, and a new experiment was carried out, in a meditation house, using these results. The treatments were: non-inoculated plants fertilized with a reduced dose of NPK (C), non-inoculated plants fertilized with a maximum amount of NPK (C+), and plants co-inoculated with Trichoderma asperellum (UFRA-06, UFRA-09, UFRA-12, and UFRA-52) and Bacillus subtilis and fertilized with a reduced dose of NPK (MIX). The experimental design was completely randomized (DIC) with ten replications. Gas exchanges from CO2 assimilation, instantaneous carboxylation efficiency, stomatal conductance, and transpiration rate were evaluated. Chlorophyll fluorescence was determined from the potential activity of photosystem II (PSII) reaction centers, photochemical extinction coefficients, electron transfer rate, effective photochemical efficiency of PSII, and non-photochemical extinction coefficients. The total chlorophyll content was measured with the aid of a chlorophyll meter and the chlorophyll a, b, and total content were quantified, as well as the quantification of soluble carbohydrates: Glucose, Sucrose, Fructose, and Starch. Growth parameters were evaluated from plant height, root length, leaf, and root dry mass, and calculated leaf area and leaf elongation rate. The nutrient content of the leaves was quantified: nitrogen, phosphorus, and potassium. The results showed that co-inoculation and doses increased leaf area, plant height, elongation rate, and leaf appearance for nitrogen and potassium, while for phosphorus the interaction was significant for root dry mass. The isolated effect of inoculation on nitrogen doses provided an increase in root and dry leaf mass, root length, and leaf elongation rate. In phosphorus doses, the isolated effect of inoculation generated an increase in root and dry leaf mass, height, root length, and leaf elongation rate. At potassium doses, co-inoculation increased root dry mass, root length, plant height, leaf area, and leaf elongation rate. Inoculation and co-inoculation showed significant increases in all indices of efficient use of the nutrient. The nutritional content as a function of co-inoculation generated an increase in the content of nitrogen, phosphorus, and potassium. The results showed that co-inoculation provided increases in CO2 assimilation, instantaneous carboxylation efficiency, stomatal conductance, and transpiration. The chlorophyll content had an increase in chlorophyll a, chlorophyll b, and the sum of chlorophylls. The content of soluble carbohydrates showed an increase in glucose, sucrose, fructose, and starch. The nutritional content of co-inoculated plants had an increase in nitrogen, phosphorus, and potassium. It is possible to state that the 7 application of biopromoters in a co-inoculated form was responsible for increasing the efficient use of nutrients, improving the photosynthetic apparatus, increasing plant growth, and providing greater efficiency in the acquisition of water and nutrients, and in the transformation of energy into productivity gains. It is possible to state that B. subtilis and T. asperellum can be used as inoculants in Marandu grass, as it increases plant growth, efficient use of nutrients, and improves the photosynthetic apparatus