Alleviation of freezing injury to Coronilla (Coronilla varia) Ground Cover by Foliar application of glycine betaine

Coronilla varia or Crownvetch is belonging to the Fabaceae family that is wildly distributed in different parts of Iran. The rapid spread of roots and shoots, as well as the ability to grow in stressful conditions, has caused it to be used to control soil erosion. In addition, the possibility of moving and regrowth has made Coronilla an appropriate alternative to turfgrass in green spaces. The aim of this study was to evaluate the response of Coronilla to freezing stress and the effect of glycine betaine on reducing seedling damage.

a factorial experiment was conducted in a completely randomized design with three replications. Low temperature for one hour in five levels [25 (control), 0, -5, -10 and -15°C] were used as the first factor and spraying with glycine betaine (one day before freezing stress) on two levels (0 and 100 mM) was considered as the second factor. After freezing stress, freezing injury, and physiological (relative water content, ion leakage) and biochemical (chlorophyll, proline, lipid peroxidation, protein, and peroxidase) attributes were measured.

According to the results, exposure to freezing temperatures (-10 and -15°C) increased the damage to Coronilla shoots. The absence of the difference between 0 and -5°C indicates that the temperature of -5°C is tolerable for the Coronilla. Foliar application of glycine betaine reduced leaf damage. The results showed that under freezing stress the relative water content of leaves and roots decreases. The lowest relative water content of leaf with 57.18% and 59.02% was related to severe stress at -10 and -15°C, respectively. Under freezing temperatures, the amount of ion leakage of roots and leaves increased, so that under severe stress of low temperature -15°C compared to 25°C, the amount of ion leakage of leaves increased by 27%. With decreasing temperature, the chlorophyll content of the leaves first increased at 0°C compared to 25°C, then decreased at temperatures below 0°C. While the use of glycine betaine (100 mM) increased the leaf chlorophyll content under freezing conditions. The results showed that with lowering temperatures, the amount of proline in leaf and root increased. In addition, foliar application of glycine betaine increased leaf proline by 7%. On the other hand, freezing stress led to a decrease in leaf (16%) and root (26%) protein at -10°C in Coronilla. In addition, compared to control with lowering the temperature, the high accumulation of malondialdehyde (leaf, 193%; root, 141%), and the activity of peroxidase enzyme in leaves (66%) and roots (156%) recorded.

Based on the results, it can be concluded that physiological and biochemical traits of Coronilla were affected by freezing stress. According to the results, leaf vulnerability was higher than the root. Low temperature caused damage to Coronilla by reducing the relative water content and ion leakage of leaves and roots. While spraying with 100 mM glycine betaine reduced the negative effects of freezing stress. Also, foliar application of glycine betaine effectively alleviates the adverse effects of freezing injury in Coronilla by increasing the accumulation of compatible osmolytes such as proline in leaves and roots.