Comparative responses of johnsongrass (Sorghum halepense (L.) Pers.) and grain sorghum (Sorghum bicolor (L.) Moench) to salinity

Abstract

Two ecotypes of S. halepense (ALA,NM) were used to compare NaCl resistance with cultivar, BTX-HEG, of S. bicolor. The objectives were: (1) to compare NaCl resistance between the two Sorghum species with whole plants and cell cultures; and (2) to determine if osmotic adjustment occurs. In the growth chamber, increased NaCl decreased growth in all three Sorghum sources. Resistance differences to NaCl among the three sources were observed with three growth parameters: leaf number/plant, total leaf area/plant, dry weight/plant part. With a 0.1 M NaCl treatment, there was a 68% reduction in total leaf area/plant in BTX-HEG as compared with only a 37% reduction in ALA. In cell culture, there was 44% reduction in the relative growth in ALA as compared with 73% reduction in BTX-HEG with 0.1 M NaCl. Less leaf growth reduction of ALA was correlated with a low content of Na+ (0.019 μ mols/gDW in ALA vs. 0.028 μ mols/gDW in BTX-HEG at 0.1 M NaCl) and Cl- (0.29 μ mols/gDW in ALA vs. 0.40 μ mols/gDW in BTX-HEG at 0.1 M NaCl). In cell culture, ALA accumulated slightly higher Na+ and Cl- on a dry weight basis than BTX-HEG at either 0.1 and 0.15 M NaCl. However, ALA also had higher K+ content (704 μmols/gDW in ALA vs. 488 μ mols/gDW at 0.1 M NaCl) and larger K+/Na+ ratio (1.33 in ALA vs. 0.98 in BTX-HEG) than BTX-HEG which may relate to the better performance of ALA in presence of NaCl. Osmotic adjustment was observed in both whole plants and cell cultures in both Sorghum species. The solutes contributing to osmotic adjustment differed in their occurrence in calli and leaves. The major solutes contributing to callus osmotic adjustment occurred in the following order: Cl- > Na+ > total amino acids. These solutes contributed 84-90% of which was lowered with 0.15 M NaCl. In leaves, the order of major solutes was: Cl- > sucrose > total amino acids; solutes contributed 50-83% to the decrease in }/s which was lowered when plants were subjected to 0.2 M NaCl. ALA of S. halepense appeared to be more NaCl-resistant than BTX-HEG of S. bicolor in whole plants as well as in cell cultures.