Compatibilidade de biouninema com agrotóxicos e promoção de crescimento de feijoeiro

Abstract

Beans are considered one of the most important crops for feeding Brazilian society. However, due to several biotic and abiotic problems that occur in bean cultivation, significant reductions in their productivity have been observed, making it necessary to adopt management tactics for this crop. These tactics can be carried out through the use of pesticides as well as biological products based on microorganisms. Among the microorganisms, the rhizobacteria Bacillus subtilis-34 stands out, which has been studied at Unimontes and has proven to be efficient in controlling phytopathogens, in addition to promoting the growth of beans, okra, tomatoes, bananas and lettuce. It is known that both biological products and pesticides are part of agricultural management. Considering the potential of B. subtilis-34 as a phytopathogen controller and growth promoter, it is essential to understand the performance of this microorganism when subjected to pesticides used in bean crops. Furthermore, there are no studies on the effect of B. subtilis-34 as a growth promoter in bean crops through soil application. Therefore, the objective of this study was to evaluate the growth of B. subtilis-34 in the presence of pesticides and its action as a growth promoter in beans. In a first experiment, the in vitro growth of B. subtilis-34 was evaluated when subjected to the presence of fungicides and insecticides, which are commonly used in bean crops. For this, two assays were used for evaluation. In Assay 1, the bacteria grew in the presence of pesticides and in Assay 2, the pesticides were added after the growth of the bacteria. These trials were developed in a completely randomized design, with 8 treatments consisting of 7 pesticides (mancozeb, captan, sulfur, thiophanate-methyl, thiophanate-methyl+chlorothalonil, thiamethoxam and pyriproxyfen+xylene) and a control (without the presence of pesticides) with 4 replicates. To evaluate bacterial growth, serial dilution was performed and the plating of the concentration of 10-5 in 7 cm diameter Petri dishes, containing Trypic Soy Agar (TSA) medium. After a period of 12 hours, the number of colony forming units (CFUs) was counted. In trial I, the fungicides mancozeb and captan inhibited the growth of B. subtilis-34, and these were classified as incompatible. In trial II, the fungicide captan completely inhibited the multiplication of the bacteria, while the fungicide mancozeb and the insecticides thiamethoxam and pyriproxyfen+xylene reduced the number of CFU. B. subtilis-34 was compatible with the pesticides thiophanate-methyl and thiophanate-methyl+chlorothalonil in both trials. The second experiment was carried out in a greenhouse and set up in a completely randomized design with five treatments, namely: 0.0 L ha-1, 2.0 L ha-1, 4.0 L ha-1, 8.0 L ha-1 of Biouninema and 4.0 L ha-1 of Biobaci® (commercial product based on B. subtilis-BV09), with six replicates. After 60 days of transplanting, the following were evaluated: number of leaves, stem diameter, plant height, SPAD, fresh and dry mass of the root, fresh and dry mass of the aerial part, number of pods, fresh and dry mass of the pods and grain weight. The dose of 4.0 Lha-1 of Biouninema provided a greater stem diameter of the bean plants while the dose of 2.0 Lha-1 of Biouninema provided a greater grain weight in relation to the other treatments.