Abstract: Using shuofeng, one cultivar of summer squash (Cucurbita pepo L. ) , as material, silverleaf whitefly induced the silvering symptoms. The effect of squash silverleaf on photosynthetic rates ( Pn ) , stomatal conductance (Gs ) , intercellular CO2 concentration (Ci ) and chloroplast ultra-structure were studied. The Pn of silvered leaves was lower than that in the healthy leaves. The Gs of silvered leaves decreased but the Ci of silvered leaves increased. Chloroplast membrane was impaired, the size and number of chloroplasts decreased. The lamellae of the grana and stroma were disintegrated gradually. The size and number of starch grains decreased. The change of chloroplast ultra-structure may be the important cause of the decrease of chlorophyllcontent and photosynthetic rate.

Key words: summer squash, silverleaf whitefly, squash silverleaf, photosynthesis, chloroplast, ultrastructure