Salinity Tolerance in Sorghum. I. Whole Plant Response to Sodium Chloride in S. bicolor and S. halepense
Based on casual qualitative observations, grain sorghum [Sorghum bicolor (L.) Moench[ is less tolerant to salt than the noxious weed and potential biomass energy crop, johnsongrass [S. halepense (L.) Pers.]. The objective was to quantitatively compare whole plant growth and physiological responses to salt stress of these two sorghum species. Salt stress was induced by adding incremental levels of NaCI to a vermiculite medium until concentrations of 0.1 and 0.2 M were attained. Leaf number and leaf area reduction and dry weight reduction in the culm and leaves in response to salinity compared to controls were greater in S. bicolor than in S. halepense. Larger leaf growth reductions in response to salinity in S. bicolor were associated with higher tissue levels of Na and CI. Sorghum halepense had a lower Na/K ratio in the leaves as well as in the roots; the cuim ratio was the same in both species. Higher ψp (0.65 MPa) and lower ψs(−2.17 MPa) S. bicolor leaves compared to the ψp (0.28 MPa) and ψs (−1.71 MPa) S. halepense leaves indicated more osmotic adjustment and more turgor maintenance in S. bicolor than in S. halepense; this response was due largely to CI and sucrose accumulation. The greater growth reduction observed in S. bicolor was associated with higher levels of CI higher Na/K ratios, and a greater capacity for osmotic adjustment. A Na exclusion mechanism appeared to be operative in both species but was more apparent in S. halepense.
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