Re-interpretation of an Experiment on the Role of Assimilated Transport Resistance in Partitioning in Tomato

The importance of transport resistance (distance between source and sink) on assimilate partitioning in tomato is questioned. Slack and Calvert ( Journal of Horticultural Science 52 : 309–315, 1977) concluded that, in tomato, excising of fruit trusses showed a direct influence of distance from source on assimilate partitioning. A dry matter distribution model for tomato, based on the hypothesis that distribution is regulated by the sink strengths of the plant organs and that no influence of transport resistance on partitioning exists, has been described and validated by Heuvelink ( Annals of Botany 77 : 71–80, 1996). Using this model, it is shown that the results of Slack and Calvert (1977) can be explained more simply on the basis of the succession of trusses with growth shifted with respect to time. Therefore, their results do not prove that transport resistance plays a role in assimilate partitioning.