Híbridos de sorgo contrastantes quanto a tolerância à seca: uma abordagem morfoanatômica, fisiológica e bioquímica

Abstract

The climate changes around the globe enhance the effects of the water deficit (WD) on plantations, bringing risks to the world’s food security. For this reason, it is necessary to focus our studies in other tolerant crops, such as sorghum, which is capable to maintain high sustainability even under conditions of water deficit. Focusing to contribute to the comprehension of the high complexities that might be associated to sorghum tolerance to drought, this study aimed to investigate the morpho-anatomical, physiological and biochemical characteristics that might be associated to responses of sorghum hybrids to drought tolerance and water deficit. The experiment was carried under greenhouse at Embrapa Milho e Sorgo. A completely randomized design in factorial scheme 2x2 was used, with two water conditions: field capacity (FC), using soil with water tension of -18 Kpa and WD, soil with water tension of -138kpa, with two hybrids, one tolerant (1G 282) and the other sensitive (AG 1060), with six replications. The WD was imposed during the first blooming phases and maintained for 12 days. After the stress period, we evaluated the following variables on the leaves of the hybrids: water potential on the leaves at noon (Ψmd), active photosynthetic area, the mean of the gas exchange, the quantic efficiency of the photosystem II, the amount of photosynthetic pigments, the activity of the antioxidant metabolism enzymes, the concentration of hydrogen peroxide, the levels of lipid peroxidation, concentration of ascorbate, amount of proline, concentration of biomolecules on the primary metabolism and the stomata density. At the end of the cycle, we evaluated the components of productivity. The 1G 282 hybrid sustained higher productivity of grains under WD condition, highlighting its tolerance when compared to AG 1060 under the same condition. Its higher tolerance is associated to the maintenance of higher water potential on the leaves, higher amount of photosynthetic pigments, reduced leaf area and higher amount of stomata under the WD condition. Hybrid 1G 282 presented higher photosynthetic rates during the stress, a highly responsive antioxidant and non-enzymatic system characterized by the stability of the carotenoids concentration, production of high concentrations of ascorbate and the increase on the activity of the SOD, CAT and APX in its leaves under the condition of water deficit. The increasing on the concentration of proteins and higher accumulation of proline and sugar a lso contributed to the higher tolerance of the hybrid under WD.