Plant growth-promoting bacteria in sorghum development in coppercontaminated soil

Copper (Cu) is a metal that can become toxic to sorghum when present in high concentrations in the soil. The use of plant growth-promoting rhizobacteria can be an alternative for the development of sorghum [Sorghum bicolor (L.) Moench] in soil contaminated with copper. The objective of this study was to determine the effect of Azospirillum brasilense inoculation on the development and copper levels of sorghum cultivated in soil contaminated with Cu, enabling the reuse of these areas. The experimental design was randomized blocks in a factorial arrangement (9 × 2), with nine doses of copper [(0: natural content of the soil), 30, 60, 90, 120, 150, 180, 240, and 300 mg of copper kg-1 of soil] with and without A. brasilense inoculation, with six replicates. In the treatment without inoculation, a dose of 200 kg-1ha was applied. Plant height (PH), stem diameter, dry mass of the air part (DMAP), volume, length, and root dry mass (RDM), relative index of chlorophyll a and b, and copper contents in DMAP and RDM were evaluated. The inoculation with A. brasilense allows a higher index of chlorophyll a and b and the development of the aerial part of the sorghum, reducing copper content in the aerial part, enabling the reuse of soil containing 52.5% clay, contaminated with up to 300 mg of copper kg-1 of soil. Inoculation with A. brasilense increases the specific surface area (SSA) of sorghum roots compared with non-inoculated plants grown only with nitrogen fertilization in soil contaminated with copper.