Effect of fruit load on dry matter partitioning in tomato

Greenhouse experiments in which tomato plants were grown for about 100 days at different levels of fruit removal, showed a strong influence of fruit load on assimilate partitioning between vegetative and generative plant parts. The fraction of dry matter distributed to the fruits (F-fruits) in the last weeks of the experiments when an almost constant distribution of dry matter was reached, could accurately be described by a saturation-type function of the number of fruits retained per truss (n(f)): F-fruits=n(f)/(2.96+/-n(f)). Hence, generative sink strength was proportional to the number of fruits in the range two to seven fruits per truss, and the average sink strength of a vegetative unit (three leaves and the stem internodes between two trusses) was 2.96 times the average sink strength of one fruit. In an experiment with either no truss pruning or every other truss removed at anthesis, the average fraction of dry matter distributed to the fruits, over a time interval between two destructive measurements, increased with average fruit number on the plant (N-f) during this time interval and could be described by: F-fruits=N-f(24.2+N-f), which is consistent with the relationship between F-fruits and n(f). The weight of individual fruits increased with decreasing number of fruits per plant, albeit less than proportionally. (C) 1997 Elsevier Science B.V.