Inoculation of corn seeds with Azospirillum brasilense in different temperatures

Resumo

Growth-promoting bacteria Azospirillum brasilense, used as an inoculant in corn culture, can be severely affected by the exposure temperature, with a lethal effect above 35°C, when cultivated alone under laboratory conditions. Such effects may limit the associative interaction between plant-bacteria, with reduced inoculation efficiency, resulting in a lower growth rate of the plant and an increase in oxidative stress. Thus, the objective of the research was to evaluate the efficiency of the inoculation process with A. brasilense in seeds and in the initial growth of seedlings of two corn cultivars submitted to different temperatures. Were utilized corn hybrids seed Syn 488 and Syn 505. The experimental design was completely randomized in a 2 x 4 factorial scheme (with and without inoculation of A. brasilense x 4 sowing temperatures: 20, 25, 30, and 35ºC), with four replications. The inoculation efficiency in corn seedlings submitted to different temperatures was evaluated through the following tests: germination, first count, seedling length and dry weight. In addition, responses at the biochemical level of the interaction (temperatures x inoculation) for the content of photosynthetic pigments and hydrogen peroxide (H₂O₂), antioxidant enzymes and lipid peroxidation were evaluated. The inoculation with A. brasilense changed the morphological and biochemical responses of corn seedlings, and the inoculation process was efficient for all temperatures tested. The best results were under temperatures 25, 30, and 35°C. Plant and bacteria when exposed to temperature conditions (30°C inoculated) showed a significant increase in plant biomass and activity of antioxidant enzymes.