Abstract: Photosynthetic physiology of silver-leaf mottling of summer squash caused by gene and virus(silver-leaf lesion) was measured.In comparison with normal green leaves at different times in the day,a decrease in net photosynthetic rate(Pn),stomatal conductance(Gs) and transpiration rate(Tr) of both forms of leaf-mottling occurs.Though Pn,Gs and Tr fluctuation urves(for the two forms of leaf-mottling) at different times in the day are dissimilar,their absolute values are actually quite close,with no significant difference(P＞0.05).No obvious difference in intercellar CO₂ concentration(Ci) for the silver leaf-mottling types is observed,and the absolute values of stomatal limiting trends are about the same.Though gene controlled silver-leaf mottling stomatal limited value(Ls) is a little higher than that of the virus controlled silver-leaf mottling,it is, however, insignificant(P＞0.05).Chlorophyll a,b and total chlorophyll content of both forms of silver-leaf mottling drops.Total chlorophyll content for the gene and virus(silver-leaf lesion) controlled silver-leaf mottling drops by 8.54% and 10.84% respectively,compared with that of green leaves.From close observation of the anatomical features of the two types of silver-leaf mottling,it is found that the upper epidermis shape and rrangement patterns of the leaves are similar,both having a little gap between the upper epidermis and the palisade cells,and the upper epidermis cells change from flat,dense arrangement to globular,thin and scattered arrangement.Based on the above mentioned results,genetic silver-leaf mottling is postulated to be a probable phytotoxic source of silver-leaves,induced by Bemisig argentifolii.