Fungos micorrízicos arbusculares (Glomeromycota) na cultura do algodoeiro (Gossypium hirsutum L.) no Oeste da Bahia

Abstract

Cotton is grown for the production of natural fibers and oil, with enormous economic importance in Brazil. Intensive systems of cotton production in the western region of Bahia State can impact the communities of soil microorganisms. This crop has a high demand for industrialized agricultural inputs. These inputs increase the cost of cotton production and promote changes in soil microbes, such as mycorrhizal fungi (AMF), which play an important role in the sustainability of agricultural systems. This study aimed to evaluate the influence of cotton growth on native populations of arbuscular mycorrhizal fungi (AMF) in the Western Region of Bahia and to evaluate the efficiency of these indigenous AMF in promoting growth of cotton plants. Soil samples were collected in cotton growing areas of conventional commercial production system, in areas of native vegetation, in areas of colored cotton family farming production system, and in native semideciduous forest, located in three municipalities of the Western region of Bahia State. Soil fertility analysis, extractions of AMF spores, mounting of slides for species identification, and establishment of trap cultures were conducted for all soil samples. The trap cultures were maintained under greenhouse conditions, for a period of one year, with Brachiaria decumbens as the host plant. AMF spores were extracted from soil samples, and mounted on slides for species identification. The first experiment was conducted with soil from Cerrado and cotton BRS 336 variety. Six AMF populations from areas of native vegetation and cotton growing areas of the western region of Bahia, and an inoculum of Paraglomus occultum were evaluated for cotton growth promotion. The second experiment was performed with cotton BRS 336 variety, on the soil from the first experiment, without re-inoculation of AMF, to evaluate the residual effect of AMF inoculation with a second crop cycle. The third experiment was conducted with the variety of colored cotton feather, BRS Safira variety, in sterilized soil from Vale region, with four AMF populations from the Atlantic semideciduous Forest and from colored cotton growing fields, and a culture of Paraglomus occultum. Sixty days after seed sowing, plants were harvested, and the following variables were evaluated: plant height, fresh and dry weight of shoot, fresh root weight and root colonization. Thirty-four species of AMF, distributed in all orders were identified in soil samples. The most frequent species were of the genus Acaulospora (10 species), followed by the genus Glomus (8 species), Dentiscutata (3 species), Ambispora, Pacispora and Scutellospora, (2 species). Species of Clroideoglomus etunicatum, Diversispora sp., Entrophospora infrequens, Gigaspora sp., Orbispora pernambucana, Paradentiscutata maritima and Paraglomus occultum were also identified. For cotton variety BRS 336, only the native AMF populations were effective in promoting plant growth. For colored cotton variety, both native populations of AMF and Paraglomus occultum were effective in promoting plant growth. The native populations of AMF were effective in promoting growth of the cotton in these soils.