Regulation of tomato fruit size by plant density and truss thinning

Abstract

SummaryThe distribution of fruit size in the yield of glasshouse-grown tomatoes was manipulated by truss thinning and by allowing side shoots to develop (“taking”) on plants grown at either low (2.04 plants m−2) or high (3.06 plants m−2) planting densities so as to raise the population densities to 3.06 shoots m−2 and 4.07 shoots m−2, respectively. By removing 30% of the available fruit from the distal end of the first three trusses, the average weight of each remaining fruit was significantly increased and the yield of small fruit (grade E) was greatly reduced. Overall, the total yield of fruit from these three trusses was reduced by 16% but the yield from higher trusses was significantly increased and almost completely compensated for the earlier loss of yield. The early and final yields from the crop grown at high density throughout were about 8% and 15% greater than at low density, respectively. The mean fruit weight (Class I) of plants grown at high density was lower than at low density, and the yield of large fruit (grade C) was lower while that of grade E was higher. The taking of side shoots lowered early marketable yields, while it increased the number of fruit produced per m2 and increased the final yield of marketable fruit, the latter only at low density. In general, the addition of side shoots lowered mean fruit weight, reduced the month-to-month variation in mean fruit weight, and reduced the yield of larger fruit and their proportion of Class I yield. The addition of side shoots at low density produced fruit of more uniform size throughout the year and the yield of grade D fruit was almost as high as from plants grown at high density throughout. These benefits were accompanied by a 5% loss of yield but from 33% fewer plants, relative to the high density treatment.