Potencial de cultivares de sorgo sacarino irrigadas com águas salinas

Abstract

Increasing production losses in agricultural areas due to salinization of soils reinforce the need to select salinity-tolerant crops, such as sorghum. However, it is important to recognize the mechanisms of tolerance developed by the plants that can support the selection of cultivars with potential use in areas whose coexistence with salinity is unavoidable. The objective of this study was to select sweet sorghum cultivars more tolerant to salinity based on morphological and nutritional characteristics aiming at the identification of promising genotypes for use in salinized areas or that do not have adequate water for irrigation. The experiment was conducted in an greenhouse using the experimental design in randomized blocks arranged in a 6 x 5 factorial scheme. There were tested six cultivars (BR 506, Willey, SF-11, SF-15, TF-17 and 467-4-2) and saline solutions with five values of electrical conductivity (0.0, 1.5, 3.0, 0 and 12.0 dS m-1) using three replicates. The saline solutions were prepared with NaCl, CaCl2.2H2O and MgSO4.7H2O salts in the ratio of 7:2:1. The application of saline solutions was started two weeks after sowing, remaining until plants collecting. In the irrigation control, load cells were installed, which functioned as weighing lysimeters and recorded readings every 15 minutes. The volume of water replacement was applied every 48 hours with a 15% leaching fraction increase. From the data collected in this experiment, this study was divided into three stages. In the first stage, the growth of the plants was evaluated for identification of cultivars with potential of cultivation under salinity. In the second stage, the mechanisms involved in salinity tolerance of sorghum cultivars (related to gas exchanges), Na+ and Cl- concentration and organic solutes in the leaves were studied. In the third stage, the effect of salts of the salt stress on the accumulation and distribution of nutrients in sweet sorghum cultivars was studied. From the results obtained it was verified that the studied cultivars BR 506, TF-17 and 467-4-2 present a higher potential of cultivation under salinity, and BR 506 is the most suitable for ethanol production. The increase in salinity causes a significant reduction in the photosynthetic activity of sweet sorghum cultivars, however, the cultivar BR 506 proves to be the most efficient. The regulation of stomatal opening increased intrinsic water use efficiency and osmotic adjustment, concentrating nutrients and non - reducing soluble sugars on the leaves represent some mechanisms of adaptation to saline stress conditions in sorghum cultivars. Nutrient accumulation was predominantly limited by the reduction of growth due to worsening salinity and, to a lesser extent, competition between soil elements, reflecting differences in leaf and root content.