Abstract: We investigated the effect of night chilling on the photosynthetic physiology of two cultivars of mango ( Mangifera indica)‘Choke Anand’and‘Khieo Sawoei. The potted mango seedlings of both cultivars were grown under the full light and 50% daylight for one year . In the following winter season (February 2006) , the seedlings were moved to a cold storage room maintaining 4℃ for seven consecutive nights and returned to their original places during the rest of the day . Photosynthetic physiology was measured before, during the treatment, and during 10 days after the treatment . Chill-night treatment resulted in strong suppression in net photosynthesis ( P_n ) , stomatal conductance ( g_s ), and maximum photochemical efficiency of PSII ( Fv/Fm ) , and increased non-photochemical quenching (NPQ) for both cultivars. Overall, the chillinginduced photosynthetic suppression was stronger in seedlings grown in full sunlight than in 50% daylight. The decrease in Fv/Fm was stronger in‘Khieo Sawoei’than in‘Choke Anand’cultivar , and the increase of NPQ was relatively higher in‘Choke Anand’compared to‘Khieo Sawoei’cultivar. Night chilling resulted in a decrease in chlorophyll content and in-crease in the carotenoid: chlorophyll ratios, the malondialdehyde (MDA) contents, membrane leakage, as well as compatible
solutes ( total soluble sugar and proline ) under both irradiances. After termination of the chilling treatment, the recovery of Fv/Fm was relatively quicker in‘Choke Anand’than in‘Khieo Sawoei’cultivar. Both cultivars showed a complete recovery after seven days of termination of the chilling treatment . These results showed that‘Khieo Sawoei’was more sensitive
to chilling than‘Choke Anand, and shading significantly alleviated the chilling - induced photoinhibition.

Key words: Chlorophyll fluorescence