Déficit hídrico e doses de nitrogênio na morfofisiologia e produção de genótipos de milho inoculados por Azospirillum brasilense

Abstract

Water stress and soil nitrogen deficiency are the abiotic stresses that most limit plant growth and development. They are presented as the main consequence in reducing the productivity of crops. Maize is one of the cereals most responsive to the water cond ition, and is often grown under conditions of water deficit and low fertility. The tolerance of maize plants to water deficit from drought periods, needs to be improved in order to meet the demands of food in areas with limited availability of water resour ces and low soil fertility. In this sense, the use of rhizobacteria appears as a tool to ameliorate these deleterious effects resulting from drought and low nitrogen applied to the soil. The inoculation by rhizobacteria that promote plant growth provides an increase in the root system, constituting a strategy of adaptation of plants in the condition of water deficit, which may reflect in tolerance a nd in higher productivity of crops. In addition, these rhizobacteria have the ability to perform biological nitrogen fixation. Thus, due to the various responses involving plant genotypes, bacteria, and environmental conditions, there is a need to better understand the mechanisms involved in this interaction. For that, two experiments were carried out in a greenhouse and two in the field. For the first two experiments we evaluated ecophysiological characteristics, foliar and root morphology and nutrient absorption. In the first trial the responses of the combination of several strains of Azospirillum brasilense in the presence and absence of water deficit were evaluated using a drought sensitive genotype. The inoculant Az1 attenuated the deleterious effects caused by drought and promoted the best growth of the root system, resulting in the tolerance of maize plants to water deficit. In the second, the evaluation was the same as in the first experiment with the difference in the maize genotype that shows drought tolerance. Az1, Az2 and Az3 inoculation can improve plant growth, nutrient uptake and mitigate the effects of water deficit on the development of maize plants. From the results of these experiments we carried out two other experiments in the field varying dose of nitrogen applied in the soil and by using a genotype sensitive to drought and the two more responsive inoculants. The effect of water deficit mitigation and soil nitrogen application with Az1 and Az2 inoculants was observed. The morphophysiological responses were improved with the presence of A. brasilense. In addition, it was possible to observe the increase in productivity with the Az2 inoculation. In the interaction of the abiotic stresses of the water deficit and of the low nitrogen, A. brasilense improves the morphophysiology and the production of the maize plants.