Shading Reduced the Injury Caused by Winter Chill on Pitaya Plant

Pitaya (Hylocereus undatus Britton & Rose) is widely cultivated in subtropical and tropical regions. Pitaya is cold-sensitive; most cultivars are injured during chilling winter periods, especially in subtropical regions. In this study, the effects of shading on the cold tolerance in pitaya plant were investigated. Pitaya plants were grown under full sunlight (control) or a shading net with a light blocking rate of about 60%. Morphological and physiological performance of the overwintering pitaya plants were compared between the control and the shaded treatment. The results showed that shading treatment markedly reduced the chilling induced tissue necrosis. Contents of chlorophyll a, chlorophyll b, and total chlorophylls (chlorophyll a+b), the chlorophyll a/b ratio, Fm and Fv/Fm were all higher in shading treatment than those in the control. Meanwhile, proline content and ascorbic acid peroxidase (APX) activity in the shading treatment were significantly increased, while malondialdehyde (MDA), the superoxide anion (O2.-) and hydrogen peroxide (H2O2) levels were significantly decreased by shading treatment. The results indicated that damage caused by chilling stress on pitaya was, at least partially, light-dependent; and in practical production, shading treatment can be used to reduce chilling injury in pitaya.