Desempenho fisiológico de sementes de soja em resposta aos estresses hídrico e térmico na fase germinativa

Abstract

Soybean is one of the main annual crops grown in Brazil, and its productivity is directly related to the physiological and biochemical quality of the seed and this quality can be affected by stress conditions, such as water and heat. In this sense, the objective of this study was to evaluate the physiological and biochemical performance of soybean seeds submitted to water deficit and thermal stress during the germination phase. The experiment was conducted in the Laboratories of Ecophysiology of Production and Plant Physiology, belonging, respectively, to the Department of Phytotechnics and Biochemistry and Molecular Biology of the Federal University of Ceará (UFC), located in Fortaleza-CE. For this study, soybean seeds of the hybrid Monsoy 8349 IPRO were used, which were submitted to water and thermal stress conditions and their physiological and biochemical aspects were evaluated. The experimental design used was completely randomized, in the split plot scheme, with four replications, with the plots by the three temperatures (20, 25 and 35°C) and the subplots defined by the six levels of osmotic potentials (0, -0.05, -0.10, -0.15, -0.20 and - 0.25MPa). The variables analyzed were: final germination percentage (%G), first germination count (PCG), germination speed index (IVG), average germination time (TMG), shoot length (CPA) and radicle length (CR), dry shoots (MSPA) and radicle (MSR), soluble carbohydrate and proline content. The low water availability negatively affected both the% G and the vigor of the soybean seeds, mainly in the lower osmotic potential (-0.25 MPa), in which there was a reduction of 23.3% in the final germination of the seeds. The temperature of 35ºC was the one that provided a reduction of 13.3% in %G, as well as promoting less vigor of the soybean seeds when compared to the other temperatures analyzed. The temperature of 20ºC, when combined with the water deficit, promoted greater reductions in PCG, in which there was a decline of 63.7% of this variable in the lower osmotic potential (- 0.25MPa) when compared with the osmotic potential 0MPa. The temperature of 25ºC provided a reduction of 61.6% in the IVG, while the temperature of 20ºC was the one that had its average germination time TMG most affected, reaching a delay of 69.15%, when comparing the extremes of its potentials osmotics. The temperature of 20ºC allowed a reduction of 73.37% in the variable CPA and 48.33% in the variable CR. In the CR/CPA ratio, it was the temperature of 25ºC that provided the greatest increase, 160.19%. The temperature of 35ºC promoted a reduction of 68.22% in the MSPA, while the temperature of 25ºC which promoted a reduction of 44.91% in the MSR. The different osmotic potentials, together with the different temperatures, directly affected the levels of organic solutes both in the aerial part and in the root of the soybean seedlings, in which the temperature of 20ºC was the one that made possible the biggest increases in the levels of soluble carbohydrates of both aerial part and radicle, 103.5% and 70.1%, respectively. The temperature of 20ºC was also the one that made possible the greatest increases in the levels of proline in both the aerial part and the radicle, 106.3 μmol g-1 MS and 127.6 μmol g-1 MS, respectively. In general, the temperature of 25 ° C proved to be the most adequate since it made possible the best physiological performance for the germinative variables, vigor and for the accumulation of carbohydrates and proline in response to water deficit.