Antioxidant-Enzyme System as Selection Criteria for Salt Tolerance in Forage Sorghum Genotypes (Sorghum bicolor L. Moench)

Abstract

The involvement of antioxidant enzyme activities in mitigating the damage of NaCl stress was studied in 26 genotypes of forage sorghum exhibiting different responses to salinity, including a local hybrid with unknown performance under salinity stress. The 2-week old sorghum seedlings were subjected to 0, 50 and 100 mM NaCl for 4 weeks, which correspond to 0.7, 8.2 and 15.11 dS m−1 salinity levels. Plants were sampled for enzyme analyses and dry weight determinations 4 weeks after starting salt treatments. Salt stress resulted in signifi cant reduction of dry weight of both tolerant and sensitive genotypes. The reduction was stronger in the later group compared with the former one at 8.2 dS m−1. In contrast, at the highest salinity level, there was sever reduction in plant dry weights for both groups, meanwhile the highest value was recorded by the local genotype. Five out of the 21 salt tolerant genotypes and the local hybrid produced the highest dry weights at 50 and 100 mM NaCl. The effect of salinity levels on antioxidant enzymes and lipid peroxidation was examined. Both salinity levels induced signifi cant increase in superoxide dismutase (SOD) activity, glutathione (GSH) levels and carotenoid concentrations in all tolerant genotypes and the local genotype compared to sensitive group. Moreover, the activities of peroxidase and glutathione reductase (GR) have increased at 8.2 dS m−l1 NaCl for most of tolerant genotypes, then the activity was declined at 15.11 dS m−1 salinity level for the second enzyme and was somehow constant for the first enzyme. There was a common trend in increasing lipid peroxidation activity for sensitive genotypes at both levels of stresses, and reducing the activity for some tolerant genotypes. Five salt tolerant genotypes and the local hybrid maintained beside high SOD, GSH, GR activities, reasonable lipid peroxidation and pigment contents. It could be concluded that the local genotype could be considered as salinity tolerant genotype as it exhibited the same trend of tolerant genotypes. Moreover, antioxidant system SOD, GSH, GR, ASPX and carotenoids could be considered as selection criteria for salt tolerance in sorghum species.