This study compared the salt tolerance of Sorghum bicolor and Sorghum sudanense plants subjected to salt stress in two distinct phases of development. We analyzed the growth, gas exchange, the relative chlorophyll content (SPAD index) and the accumulation of organic and inorganic solutes. The experimental design was a randomized 2 × 3 × 2 factorial that included two species (S. bicolor and S. sudanense), three concentrations of salts in the irrigation water (electrical conductivities of 0.0, 4.0 and 8.0 dS m-1) and two periods of salt stress application to the plants [from sowing until 24 days later (Phase I) and from the 25th to the 49th day after sowing (Phase II)] with five replicates. Based on gas exchange and growth results, the plants in Phase I were more sensitive to the effects of salt stress than were those in Phase II. However, we did not observe major differences in salt tolerance between S. bicolor and S. sudanense. The Phase I sorghum plants showed a lower accumulation of organic solutes and a higher concentration of toxic ions, which confirmed that Phase I was more sensitive to salinity than Phase II.
Key words: Photosynthesis, plant growth, salinity, sorghum, salt tolerance.
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