INTERFERENCE OF HERBICIDES ON THE ASSOCIATION OF THE BACTERIA Azospirillum brasiliense IN SOYBEANS AND TOXICITY OF HERBICIDES TO THE BACTERIA

• Grant number: 24/16615-9
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: February 01, 2025
• End date: January 31, 2026
• Field of knowledge: Agronomical Sciences - Agronomy - Crop Science
• Principal Investigator: Patrícia Andrea Monquero
• Grantee: Carina de Fátima Felippe
• Host Institution: Centro de Ciências Agrárias (CCA). Universidade Federal de São Carlos (UFSCAR). Araras , SP, Brazil

Abstract

Inoculation with Azospirillum brasiliense through biological nitrogen fixation (BNF) and the production of phytohormones results in improvements in soybean productivity, promoting the development of the root system and the absorption of water and nutrients. Post-emergent herbicides used on this crop can have a toxic effect on bacterial cells. The aim of this study is to evaluate the co-inoculation of Azotrop (Azospirillum brasiliense) and Rizokop (Bradyrhizobium japonicum) in soybeans and the toxicity of post-emergent herbicides to A. brasiliense. The first trial will have a completely randomized design in a 2 x 6 + 2 factorial scheme, with two phenological stages for the application of the herbicide treatments and 6 herbicide treatments with two control treatments and four replications. The experiment will be carried out in a greenhouse in pots with a volumetric capacity of 10 liters, using soybeans with Enlist technology inoculated with the commercial product Rizokop + Azotrop. After inoculation, the plants will be sprayed with the following herbicide treatments: glyphosate, ammonium glufosinate, 2,4-D, glyphosate + ammonium glufosinate, glyphosate + 2,4D and glyphosate + 2,4D + ammonium glufosinate applied at two different phenological stages: V2 and V3 and with two controls: without herbicides and with inoculation and without herbicides and without inoculants. The quantity and functionality of bacterial nodules will be assessed at the V5 stage. When the soybeans reach R8, the plants will be evaluated in terms of the number of pods per plant, the number of grains per plant, plant height (cm) and the biomass of the roots of each plant (g). The in vitro sensitivity of the A. brasiliense bacteria to herbicides will be assessed using the minimum inhibitory concentration (MIC) technique, this being the first in vitro test. The experimental design will be entirely randomized with four replicates in a 3 x 5 factorial, with the factors represented by 3 herbicides: glyphosate (750 g/L a.e. ha-1), ammonium glufosinate (500 a.e. ha-1), 2.4-D (837.5 a.e. ha-1) in 5 doses: commercial dose (CD), double (2DC), one and a half of the commercial dose (1.5 CD), half (½DC) and a quarter (1¿4DC), as well as a control without herbicide. In the second in vitro trial, A. brasiliense cells will be assessed for their ability to produce indole-acetic acid (IAA) when in contact with the following treatments: glyphosate, 2,4-D and ammonium glufosinate applied at commercial doses and mixtures of glyphosate + 2,4D, glyphosate + ammonium glufosinate and glyphosate + 2,4-D + ammonium glufosinate. The bacterial cells will be tested for EIA production by adding Salkowiski's reagent. The data from the experiments will be subjected to analysis of variance and, when significant, the means will be compared using the Tukey test at 5% probability.