Abstract: Changes in chlorophyll content, chlorophyll fluorescence parameter (Fv/Fm) , MDA content and SOD activity in the leaves of six Phalaenopsis cultivarswere studied during different low temperature treatments, and during recovery. The results showed that the cold damage on leaves at 11℃/6℃ was different among cultivars. The damage on leaves of GL11 and JT944 wasmore serious than NK1 and GL14. After 10 d of recovery, chlorophyll content and Fv/Fm in NK1 and GL14 were 84.9% , 43.3% , 91.3% and 24.8% of those before cold treatment, respectively. In contrast, chlorophyll content and Fv/Fm in GL11 and JT944 at 10 d of recovery were only 2.3% , 6.3%, 0 and 0, respectively. NK1 and GL14 had a higher recovery capacity. So it is concluded that NK1 and GL14 were cold2tolerant and GL11 and JT944 were cold-sensitive.The rests were intermediate in cold tolerance, GL11 was the only cultivar that was severely injured under 14℃/9℃, which indicated that the threshold low temperature at night endurable bymost of Phalaenopsis cultivars was below 9℃. The changes in chlorophyll content, Fv/Fm and SOD activity under different cold temperatureswere significant and could be used to indicate the cold tolerance of Phalaenopsis. MDA content did not show consistent changes under cold temperatures.

Key words: Pha laenopsis, Cold tolerance, Chlorophyll content, Fv/Fm, MDA, SOD