Plant growth, gas exchange characteristics, chlorophyll fluorescence, disease index, and disease prevention efficiency of LaCl3 in tobacco （Nicotiana glutinosa） plants infected by Fny-CMV （fny stain of cucumber mosaic virus） strain were determined. Leaf area, chloro-phyll and carotenoid contents, maximum photosynthesis rate, apparent quantum yield, and carboxylation efficiency dramatically decreased after 5 weeks post inoculation. The plants infected by Fny-CMV only presented much severer symptom than those infected in the presence of appropriate concentration of LaCl3. ETR （apparent rate of photosynthetic electron transport）, NPQ （nonphotochemical quenching）, qP （coef-ficient of photochemical quenching）, and yield （II） in infected tobacco plants obviously reduced in higher light intensity after 5 weeks post inoculation. And these fluorescence parameters in Fny-infected plants obviously reduced compared with those in the plants infected by Fny in the presence of LaCl3. Together with the growth status and disease index, it revealed that exogenously appropriate concentration of LaCl3 could significantly alleviate the damage of tobacco seedlings caused by Fny-CMV.
