Two instead of three leaves between tomato trusses: measured and simulated effects on partitioning and yield

Commercial tomato cultivars initiate three leaves between trusses. It is expected that in a cultivar with only two leaves between trusses assimilate partitioning towards the fruits and therefore yield would be favored. However, a lower number of leaves on the plant reduces leaf area index (LAI) and may therefore reduce light interception and total biomass production, affecting yield negatively. The effect of the number of leaves between trusses was investigated in a simulation study and a greenhouse experiment. In the photosynthesis-driven model TOMSIM, two leaves per truss were simulated by reducing the sink strength of each vegetative unit by 1/3. Seven fruits per truss were assumed. Reduced vegetative sink strength increased partitioning to the fruits over a whole season from 66% to 74%. However, yield increased only marginally (1.5%), as average LAI decreased from 2.4 to 1.7 m2 m2 and hence total biomass production was reduced by 9.5%. To avoid this reduction in total biomass production, the removal of old leaves was delayed by 2 weeks. This resulted in an average LAI of 2.3 m2 m2, identical total biomass production, and yield improved compared to the control with 12.8%. In the greenhouse experiment, control plants (no leaf pruning) and plants where the second leaf of each vegetative unit was weekly removed when it was only 1-3 cm long, were grown. To compensate for a decrease in LAI, pruned plants were also grown at 3.8 plants m2. All plants were pruned to 6 fruits per truss. Leaf pruning increased partitioning to the fruits, averaged over the period from 18 February to 20 May, from 57% to 61%. Average LAI was 2.9, 2.4 and 3.6 m2 m2 for control, leaf pruning and leaf pruning & increased density, respectively. Leaf pruning significantly reduced total biomass by 11% whereas fruit yield was hardly affected. Leaf pruning & increased density unexpectedly resulted in only 58% of dry matter allocated to the fruits. Increasing density increased biomass and fruit yield per m2 by 29% and 17%, respectively. It is concluded, based on simulation results and experimental data, that a tomato cultivar with 2 instead of 3 leaves between trusses would improve yield, when combined with measures to keep LAI sufficiently high