Prioritization of feasible physiological parameters in drought tolerance evaluation in sorghum: a grey relational analysis

Identification and evaluation of drought tolerant germplasm is the primary step for sorghum (Sorghum bicolor L. Moench) breeding and utilization under drought conditions. The objective of this study was to use a grey relational analysis to investigate the role of feasible physiological parameters in evaluating drought tolerance in sorghum. Four sorghum varieties were cultivated in pots with two water treatments, including normal watering (75–80% of the soil moisture capacity) and water deficit (45–50% of the soil moisture capacity), which occurred at jointing stage, anthesis and filling stage, respectively. Drought tolerance index of yield was used as the key indicator to evaluate sorghum performance under drought. The grey relational degree of the investigated parameters decreased in the order of transpiration rate, stomatal conductance, photosynthetic rate, soluble sugar content, proline content, relative water content, activity of catalase, activity of superoxide dismutase and activity of peroxidase, implying that drought tolerance for guaranteeing sorghum yield formation was the most related to gas exchange parameters. Water content was a very sensitive parameter of plant growth under drought stress and was more important as compared to the activities of antioxidant enzymes. Results of this research suggested that feasible physiological parameters could be used in the evaluation of drought tolerance to improve the efficiency and accuracy of selection.