Strawberry physiological and biochemical responses to chilling and freezing stress and application of alleviating factors as countermeasures

BACKGROUND: Strawberry is usually cultivated in unheated glasshouses or outdoors, suffering many times by low temperatures during the winter period, with the danger of plant losses. OBJECTIVE: To investigate the efficacy of various alleviating agents against chilling and freezing stress. METHODS: Strawberry plants were foliarly treated with various alleviating substances, i.e. glycine betaine, trehalose, salicylic acid and proline and exposed to 5 °C (chilling treatment) for three weeks followed by a three hour exposure to – 10 °C (freezing treatment), while control plants were growing under 20 °C. At the end of each period polyamine and carbohydrate concentration, antioxidant enzymes activities, total phenols and proline concentration, chlorophyll concentration, lipid peroxidation, electrolyte leakage and H2O2 production in the leaves were measured. RESULTS: All applied products alleviated chilling stress, inducing lower electrolyte leakage, but higher sucrose and fructose concentration in the leaves compared to control. Under freezing temperature, salicylic acid proved to be the most efficient based on the lowest leaf damage observed, followed by trehalose and proline. CONCLUSIONS: Salicylic acid was the best alleviation agent based on leaf damage evaluation, by inducing low chlorophyll a degradation, low superoxide dismoutase, peroxidase and polyphenol oxidase activities as well as low putrescine concentration.