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Running head: Effects of daylength and leaf removal on tomato * Author for correspondence. SUMMARYWhile low intensity long-day (LD) lighting has been shown to enhance the growth of young plants under low light levels, the effect on the yield of a long-season glasshouse tomato crop has not been previously examined. LD were provided by the use of tungsten lamps (2.8 µmol m -2 s -1 at approx. 0.5 m from the ground) between 04.00 h to sunrise and from sunset until 20.00 h (GMT). LD lighting increased the leaf chlorophyll contents, and the numbers of flowers and fruits set per truss when the plants were young. However, this treatment did not affect the total yield of tomatoes.Different leaf removal treatments were applied within each glasshouse compartment.A previous experiment had shown that reducing the leaf area index (LAI) from 5.2 to 2.6, by removing old leaves, did not affect yields. It is also thought that the removal of young leaves reduces the total vegetative sink-strength and favours assimilate partitioning into fruit. Therefore, removal of young leaves could benefit yield. In the present experiment a third of the leaves were removed in March (those immediately below each truss) and subsequently every third leaf was removed at an early stage.This reduced the LAI from 4.1 to 2.9 and resulted in a loss of yield from 3 to 4 weeks after leaf removal until the end of the experiment, at which point there was an 8% loss of cumulative yield, due to a reduction in the average number of fruits set per truss and mean fruit weight. We postulate that light which would have been intercepted by young photosynthetically efficient leaves at the top of the canopy was intercepted instead by older leaves which were less efficient, reducing the net canopy In both studies increased chlorophyll contents were observed when growth was enhanced as a result of LD. Based on the response presented by Gabrielsen (1948), Hurd (1973 estimated that the observed increase in chlorophyll content could account for a 6% increase in photosynthesis under the conditions used