Effects of drought preconditioning on freezing tolerance of perennial ryegrass

Abstract

Predicted increases in winter temperatures may negatively impact winter survival by preventing maximal cold acclimation prior to freezing temperatures. Accordingly, research is needed to identify strategies that may help promote cold acclimation and increase freezing tolerance. Therefore, the objectives of this research were to (i) examine the effects of drought preconditioning (DP) on freezing tolerance of two perennial ryegrass (Lolium perenne L.) cultivars (‘Buccaneer’ and ‘Sunkissed’) under both non-cold acclimating (20°C) and cold acclimating (2°C) conditions; and (ii) examine the physiological and biochemical changes in leaves and crowns of perennial ryegrass in response to DP. Plants of ‘Buccaneer’ and ‘Sunkissed’ perennial ryegrass were subjected to the following treatments in a controlled environment chamber: (i) well-watered at 20°C, (ii) DP at 20°C, (iii) well-watered at 2°C, and (iv) DP at 2°C. Leaf and crown tissues were harvested for analysis of freezing tolerance (lethal temperature resulting in 50% mortality, LT50), nonstructural carbohydrates, proline, soluble protein, and antioxidant enzyme activities. Drought preconditioning resulted in an improvement in freezing tolerance (lower LT50) for Buccaneer, but had no significant effect on freezing tolerance of Sunkissed. Furthermore, DP resulted in increases in carbohydrate, proline, and soluble protein contents, but this response was dependent upon cultivar, tissue, and temperature regime.