Defícit hídrico em soja com tipo de crescimento semideterminado para a região do Matopiba

Abstract

The soybean is one of the most cultivated legumes in the world. In Brazil, more than 33 million hectares were planted in soybeans for a production of more than 114 million tons and in the state of Tocantins, the planted area was over 940 thousand hectares with a production of 2.9 million tons in the 2016/2017 harvest. However, soybean crops are affected by climate change and the water deficit that lead to significant reductions in yields. Considering the relevance of this culture in the national context, this study aimed to characterize soybean lineages with semi-determinate growth habit developed by the Federal University of Tocantins breeding program for the water deficit, analyzing the agronomic, physiological and biochemical characters. The work has been divided into two chapters. The objective of the first chapter was to evaluate the effects of the deficit in the gas exchange, agronomic and biochemical variables of the studied lineages at the reproductive stage of flowering at the beginning of grain filling in the municipality of Gurupi-Tocantins. The second chapter aimed to study the effects of the water deficit in the period of reproduction, from the beginning of the grain filling to the full filling. Genotypes were subjected to water restrictions with 30% and 50% reduction of field capacity. In general, the water deficit of 30 and 50% applied to flowering did not affect these following variables: yield per plant, weight of 100 seeds, total number of pods, total number of seeds per plant, stem diameter, first pod insertion and percentage of blank pods. Likewise, the amino acid proline was affected by water stress and the genotype 4 had the highest proline concentration. When submitted to higher intensity water deficits, reductions were recorded for the variables such as stomatal conductance, transpiration, water use efficiency and photosynthesis. In the grain filling, even with the reduction of stomatal conductance, the internal carbon concentrations in general were not changed in treatments without stress and stress of 30 and 50%. When compared to with stress and without stress, the level of proline was affected for all genotypes. There was no statistical difference among the genotypes for the agronomic variables: stem diameter, first pod insertion, blank pod percentage, pod number per plant, total number of seeds per pod, yield per plant and weight of one hundred seeds. The genotypes 2 and 4 presented positive results and were consequently selected to continue in the breeding program.