Abstract: In order to elucidate one mechanism underlying plant resistance to downy mildew（DM）disease，Vitis amurensis‘Zuoshanyi’（a DM-tolerant cultivar）and‘Shuangfeng’（a DM-susceptible cultivar）were inoculated with Plasmopara viticola，and chlorophyll fluorescence IMAGING-PAM was used to analyze the photosynthetic changes in leaves. After 3 days of inoculation，spot lesions caused by DM were observed，and chlorophyll fluorescence parameters were significantly altered in the infected leaf tissues. In the leaf spots by 7 days of inoculation，the amplitudes of Fv/Fm，ФPSII，Y（NPQ），and Y（NO）changes were higher in Zuoshanyi（–73.42%，–100%，–49.64%，+ 285.21%，respectively）than in Shuangfeng（–22.98%，–28.17%，+ 5.62%，+ 26.18%，respectively）. Compared to the control leaves，ФPSIIand rETR in tissues surrounding the infection sites were higher in Zuoshanyi but lower in Shuangfeng. Therefore，withered spots period of Zuoshanyi was earlier than Shuangfeng，which lead to fluorescence parameters in withered spots changed rapidly，at the same time，ФPSII and rETR of the surrounding tissues of infected sites in Zuoshanyi was higher than in Shuangfeng，which enhanced the ability of DM inhabitation. ФPSII and rETR might be used as an indicator to screen DM-resistant cultivars of V. amurensis.

Key words: Vitis amurensis, downy mildew, chlorophyll fluorescence imaging