Azospirillum brasilense e fungos micorrízicos arbusculares no desenvolvimento do sorgo granífero e sua ocorrência em solo contaminado com cobre

Abstract

The inoculation of Azospirillum brasilense bacteria and arbuscular mycorrhizal fungi to plants can improve their development and productivity, and also reduce the amount of inorganic fertilizer applied to the plants. However, the increase in copper concentration in the soil, especially due to the intensification of anthropic activities, promotes a selection pressure mainly on fungi and bacteria, which induces the maintenance of only the most resistant species in the soil. Therefore, the general objective of this study was to analyze the influence of Azospirillum brasilense and different species of arbuscular mycorrhizal fungi on the development and productivity of grain sorghum, as well as the effect of soil contamination with copper on the population of Azospirillum brasilense and on the number of spores of mycorrhizal fungi existing in soil cultivated with agricultural crops. To meet this objective, three scientific studies were developed, the first of which aimed to evaluate the ability of Azospirillum brasilense inoculation to partially replace inorganic fertilizer in the grain sorghum crop, considering its development and productivity; the second, to select species of arbuscular mycorrhizal fungi efficient for the development and productivity of two grain sorghum cultivars fertilized with inorganic fertilizer; and the third, to analyze the effect of copper contamination on the population of Azospirillum brasilense and arbuscular mycorrhizal fungi in soil cultivated with different agricultural crops. The results showed that the inoculation of Azospirillum brasilense in grain sorghum cultivated with inorganic fertilizer increased the root system, NDVI, grain protein and grain yield. Sorghum plants inoculated with Azospirillum brasilense grown with 75% of the fertilizer dose showed grain yield and grain protein content equivalent to those grown with 100% of the recommended fertilizer dose without inoculation. Inoculation of Azospirillum brasilense has the ability to partially replace inorganic fertilizer in grain sorghum. The mycorrhizal species Scutellospora pellucida and Acaulospora scrobiculata increased the thousand grain weight, the phosphorus and potassium contents of the grains and the grain yield of grain sorghum, Acaulospora scrobiculata also increased its vegetative development as well as Glomus formosanum. The inoculation of mycorrhizal fungi in sorghum increased the NDVI and the protein content of the grains. Soil contamination with 400 mg of copper kg-1 reduced the number of spores of mycorrhizal fungi present in soil cultivated with grain sorghum and wheat, as well as the population of Azospirillum brasilense in soil cultivated with grain sorghum and maize.