The leaf photosynthetic potential was evaluated based on the electron transport rate (ETR) of the photosystem Ⅱ in a sweet potato leaf the surface of which was sealed with Vaseline to stop the gas exchange flow. Directly after the total carbon assimilation rate (Pg_2%, or photosynthetic potential) of a leaf was measured in 2%-O_2 air, the leaf was sealed with Vaseline and the ETR was measured. These measurements were tested using young to aged leaves at different light intensities. A close positive relationship was found between Pg_2% and ETR. This result indicates that Pg_2%, or the leaf photosynthetic potential, is estimated by this method. When the detached leaf was Vaseline-sealed and placed in a moistened vinyl-bag in the shade at room temperature, the activity of the preserved leaves was sustained for more than two hours after sampling. Since the chlorophyll fluorescence of a Vaseline-sealed leaf can be monitored within a few minutes, a lot of stocked leaves are possible to be measured collectively. The value obtained is used as a selection criterion for the leaf photosynthetic.
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