Análise da inoculação de Azosporillum brasilense e de Bacillus spp. em milho sob déficit hídrico

Abstract

Drought severely affects plant productivity and reduces the economic viability of agriculture. Limited water resources and the high cost of irrigation are important factors that force farmers to reduce irrigation, requiring management strategies that minimize costs, without, however, sacrificing crop performance. In this context, the suboptimal irrigation technique becomes an interesting alternative. Likewise, the use of plant growth-promoting rhizobacteria (RPCP) may have a promising role in coping with the deleterious effects of low water availability. In view of the above, homologous strains of Azospirillum brasilense and Bacillus spp were inoculated in hybrid maize seeds and two assays were conducted. The first experiment, carried out in a greenhouse, aimed to evaluate the effects of inoculation and co-inoculation of strains of Azospirillum brasilense and the mixture of Azospirillum brasilense + Bacillus spp on root development, physiological responses and productive performance of corn hybrids with contrasting drought characteristics (DKB390 and P30F53), and exposed to two water regimes (Field Capacity and Water Deficit). The second trial was carried out in the field, with the objective of evaluating the potential effects of inoculation and co-inoculation of strains of Azopirillum brasilense and Bacillus spp. on the development and productive performance of DKB390 hybrid maize submitted to different irrigation gradients. The plants were exposed to three water regimes: full irrigation, moderate water deficit and severe water deficit. The results observed in the greenhouse experiment showed that the inoculants promoted beneficial effects for both maize genotypes exposed to water deficit conditions, with a consequent increase in grain yield. The rhizobacterium Azospirillum brasilense promoted an increase in all root characteristics analyzed in the hybrid DKB390. Co-inoculation with Azospirillum + Bacillus was responsible for promoting higher averages in all parameters evaluated for the hybrid P30F53. In the Fv/Fm ratio there was inhibition of photosystem II only in plants exposed to water deficit after seven days of stress, however the inoculant Azospirillum brasilense provided higher values for both DKB390 and P30F53. Different genetic materials, with divergent behaviors to drought, behave differently in relation to the plant-bacteria association. In the second assay, the analyzes showed that the RPCP interfered in the regulation of the analyzed antioxidant enzymes, attenuating the oxidative damage in plants under water deficit. The Azospirillum + Bacillus treatment acted on the development of the root system, generating an increase in the number of roots and the formation of longer, deeper and thinner roots. The treatments Azospirillum brasilense and the combination Azospirillum + Bacillus, promoted greater mass of ears and mass of grains in comparison to the other treatments, in plants exposed to severe water deficit.