AVALIAÇÃO DE CEPAS BACTERIANAS DE Bacillus PARA PROMOÇÃO DE CRESCIMENTO VEGETAL EM DUAS CULTIVARES DE ALGODÃO

Abstract

The search for and understanding of the functions of rhizobacteria that promote plant growth and have the potential for biocontrol has become increasingly frequent due to the need for more sustainable agriculture, with less use of chemical inputs and which generates greater productivity. Cotton is a crop that requires a supply of nutrients including nitrogen, phosphorus, and potassium that must be available in the soil for better cotton fiber quality. Furthermore, there is a need to use chemical pesticides to control diseases found in this crop. Although cotton farming is of great economic importance for the country, its production cost is quite high. The present work aims to isolate bacteria of the genus Bacillus from cotton and evaluate the plant growth promotion parameters by the isolates found in the species, as well as observe the potential of the isolates to inhibit the growth of phytopathogenic cotton fungi. Cotton root samples were used to isolate the bacteria. The isolation method used was pasteurization, which selects endospore-producing isolates. The bacterial isolates were incubated in Nutrient Agar medium, in which they were subcultured and purified for subsequent storage and evaluation of plant growth promotion characteristics. 54 bacterial isolates were obtained, and 46 were sequencing, these 43 of which were Bacillus tested for calcium phosphate solubilization, IAA (indole-3-acetic acid) production, CMCase (carboxymethylcellulase) activity, and siderophore production. The bacterial isolates obtained were subjected to in vitro confrontation tests to verify their potential to inhibit the growth of cotton phytopathogens. The halos around the bacterial colonies were measured and then the inhibition rates, in percentage, were calculated. From the biochemical tests to promote plant growth, bacterial isolates were selected that showed better performance for the in vivo test in a greenhouse with the cotton cultivars FM 985 and TMG 47. The treatments were carried out using 1 mL (108 CFU/mL) of bacterial strain culture and a commercial inoculant as control, with nine replicates used for each treatment, observed for 110 days. In the experiment, the plants were evaluated for morphological, phytochemical, and macronutrient parameters. Considering the morphological parameters, there was a positive relationship between the cultivars and the treatments made with bacteria, with an increase in height, fresh mass of the aerial part, dry mass of fruits and roots, volume and length of the root, and number of leaves. Regarding phytochemical parameters, improvements were observed in the concentrations of total sugars, ascorbate peroxidase, phenolic compounds, free amino acids, total sugar, chlorophyll A, reducing sugars, flavonoids, catalase, and chlorophyll B. The bacterial isolates showed potential in inhibiting the growth of the pathogenic fungi Corynespora cassiicola and Fusarium oxysporum f. sp. vasinfectum, with rates of up to 71.89% inhibition of fungal growth. Through the results obtained, it was possible to conclude that the isolates have characteristics that promote plant growth, highlighting the P6T32B7 isolate that obtained the best results in tests carried out on the plant, showing potential for future tests to be carried out in the field. This isolate has the potential for future field testing and possible product formulation.