Bacterial biocontrol agents of rice diseases: compatible with pesticide and effects on rhizospheric soil microbiota

Abstract

The aim of this study was to determine the behaviour of bacterial biocontrol agents (BBAs) selected to control disease in irrigated rice, in the presence of pesticides, and to study changes in the soil microbiota. We assessed the compatibility between these BBAs and pesticides using diff erent doses of each compound, besides the impact of the BBAs on the quality and diversity of the soil microbiota under fi eld conditions. For the microbial evaluations, rice seeds were treated with the same BBAs, in addition to the following combinations: DFs-C6 (DFs185 (Pseudomonas synxantha)/DFs306 (/unidentifi ed)); DFs-C7 (DFs306/DFs416 (Bacillus sp.))and DFs-C8 (DFs185/DFs306/DFs416). Saline solution was used for the control treatment. Soil samples were collected close to the roots to evaluate basal respiration, organic matter, carbon, and microbial biomass. EcoPlate TM microplates were used to determine the activity and diversity of the microbial metabolic profi le. All the BBAs (DFs185, DFs223 (P. fl uorescens), DFs306 and DFs416) were tolerant to the fungicides and herbicides regardless of the dose, whereas tolerance to the insecticides occurred only in the DFs416 isolate. Resistance, however, was only seen in the DFs185 (pyraclostrobin + epoxiconazole) and DFs223 (azoxystrobin) isolates. There were signifi cant changes to the soil microbiota, especially with the DFsC06 treatment, which was the only treatment to increase the microbial biomass and quotient. Little or no diff erence was found in microbial metabolic activity or diversity. These results suggest the potential use of these bacterial treatments in integrated pest management, as they are resistant/tolerant to many pesticides used in rice cultivation, and some of them had a positive impact on the soil microbiota.