Mother corm origin and planting depth affect physiological responses in saffron (Crocus sativus L.) under controlled freezing conditions

Considering the prevalence of cold and dry winter in many saffron cultivation regions, the freezing-induced damage is one of the most adverse factors increasing electrolyte leakage and reducing corm growth. These effects justify the necessity of studying agronomic strategies to promote plant tolerance to freezing stress. Herein the effects of planting depth, freezing injury and mother corm origin on some biochemical responses and regrowth mechanisms of saffron were evaluated based on a completely randomized design arranged in factorial with four replicates. In this study, different planting depths (10, 15 and 20 cm), mother corms harvested from different farms (1-4 years old), and freezing stress (natural temperature, - 10 and - 20 degrees C) were tested. The maximum N, P, and K concentrations in leaf, root and corm mass were found when mother corms originated from a 4-year-old farm. By contrast, the minimum values were obtained in the mother corms originating from a 1-year-old farm. The same trend was also observed for proline accumulation in above- and underground organs. With dropping temperature, electrolyte leakage in leaf (ELL) and whole underground part (ELU) significantly increased, while the proline accumulation increased. Moreover, ELL and ELU significantly decreased with increasing planting depth. Although chlorophyll a, chlorophyll b and carotenoid contents decreased on account of freezing stress, the pigments recovery process accelerated at -20 degrees C, compared with -10 degrees C. Moreover, the highest recovery rate of chlorophyll a, chlorophyll b and carotenoid was observed when the planted corms originated from a 4-year-old farm. Overall, it seems that mother corms planting, harvested from 4-year-old farms, at 20 cm soil depth can effectively alleviate the adverse effects of freezing injury in saffron.