Effects of osmoprotective compounds on freezing tolerance in chestnut (Castanea sativa) leaves

The European chestnut is an interesting productive alternative for farmers in southern Chile. However, in recent years, climatic variability with the occurence of late spring and early summer frosts has caused severe damages to new shoots and leaves of young chesntut trees, especially in the training phase and on herbaceous tissues. Low temperatures negatively affect growth, productivity and trigger a series of morphological, physiological and biochemical changes in fruit trees. The experiment aimed to evaluate the effect of osmoprotective compounds on freezing tolerance in chestnut leaves. The trial was conducted in a three-year-old orchard cultivar ‘Cittá di Castello’ managed with a leader training system in Vilcún County, La Araucania region, southern Chile. A randomized complete block experimental design was employed with three replications of 10 trees per treatment with a planting layout of 8×7 m (178 trees ha^-1). The treatments were the following: -OP (control water), salicylic acid at 50 (SA50), 100 (SA100), 150 (SA150) and 250 mg L^-1 (SA250), ascorbic acid at 50 (AA50), 100 (AA100), 150 (AA150) and 250 mg L^-1 (AA250). Whereas a comercial biostimulant (Ascophyllum nodosum) ST3 was sprayed at 3 mL L^-1. The treated plants showed less cold damage compared with untreated chesnuts trees. The highest levels of chlorophyll content were obtained in leaves treated with AA50 (2.98 mg g^-1 FW), and the highest photosynthetic activity was determined during December for the treatment AA50 (16.01 µmol CO₂ m^-2 s^-1). With respect to the total phenol content treatments SA100 and ST3 reached the highest values, 52.33 and 49.73 mg GAE g^-1 FW (fresh weight), respectively. In relation to lipid peroxidation (LP), the highest malondialdehyde (MDA) values were obtained for the treatments AA50 (66.37 nmol MDA g^-1 FW) and SA150 (65.73 nmol MDA g^-1 FW).