Low,non-freezing,temperature may delay senescence,reduce disease,and control insect pest in stored citrus fruit,but it may also cause chilling injury (CI).Exposure of chilling-sensitive citrus cultivars to non-lethal high temperature conditioning or hardening treatments may increase their chilling tolerance. Fortune mandarin is very sensitive to chilling and,therefore,a good model system to study the basis of CI.Furthermore,this cultivar is very useful for the understanding of the responses associated with the heat-induced chilling tolerance since conditioning fruit of this cultivar at 37℃ for 3 days prior to cold storage is very effective reducing CI.Physiological and biochemical studies have provided very valuable information about the involvement of hormones,oxidative stress,lipids,carbohydrates and phenolic metabolism in low temperature tolerance and highlight the relevance of the antioxidant enzymatic system,of the enzyme phenylalanine ammonia-lyase and of the hormone ethylene in this process.