INFLUENCE OF SINK-SOURCE INTERACTION ON DRY-MATTER PRODUCTION IN TOMATO

Sink-source ratio in tomato was manipulated, in six glasshouse experim ents, by fruit pruning (trusses pruned to two to seven fruits immediat ely after fruit set of each truss), truss pruning (removal of every ot her truss at anthesis) and truss pruning in plants with two shoots. Pe riodic destructive harvests were conducted for about 100 d after flowe ring of the first truss. Dry matter production was not influenced by s ink-source ratio, whereas dry matter distribution between fruits and v egetative parts was greatly affected. The fraction of dry matter distr ibuted to the fruits at the end of the fruit pruning experiments (F-fr uits) could be described accurately as a saturation-type function of n umber of fruits retained per truss (N-1): F-fruits = 0.660 (1 - e(-0.3 41Nf)). Specific leaf area and internode length decreased and plant le af area increased when sink-source ratio was reduced. Removal of every other truss at anthesis did reduce dry matter partitioning into the F ruits, but it did not influence internode length. Plant development (n umber of visible leaves at the end of the experiments) was not influen ced by sink-source ratio. In four experiments some plants were pruned to one fruit per truss. Final dry matter production was 8-24% lower fo r these plants, compared with plants with more than one fruit per trus s. This was, at least partly, the result of less light interception by these plants, which had strongly curled leaves pointing downwards. Re sults indicate that effects of sink demand on dry matter production pe r unit of intercepted radiation and probably on leaf photosynthetic ra te in commercial tomato production can be ignored.