DRY-MATTER PARTITIONING IN A TOMATO CROP - COMPARISON OF 2 SIMULATION-MODELS

TOMSIM(1.0) and TOMGRO(1.0) are two dynamic models for tomato growth a nd development. Their sub-models for dry-matter distribution between l eaves, stem and fruits were compared and discussed. In both models the simulated dry-matter distribution is regulated by the relative sink s trengths of the plant organs. These sink strengths are quantified by t he potential growth rates of individual organs, i.e. the growth rates under conditions of non-limiting assimilate supply. This approach is g eneral and not limited to the tomato crop. In TOMGRO(1.0), fruits, lea ves and internodes stay within age classes and move from class to clas s during development, whereas in TOMSIM (1.0), record is kept of every fruit truss separately but leaves and internodes are lumped together (i.e. no record of weight or leaf area per age class as in TOMGRO(1.0) ). In TOMSIM(1.0), vegetative sink strength is a constant, whereas in TOMGRO(1.0) it is calculated from potential area expansion rate of lea ves and specific leaf area. In both models, the ratio between leaf gro wth and stem growth is constant. In TOMGRO(1.0) there is a feed-back m echanism which controls the vegetative/generative balance: a higher de mand/supply ratio for assimilates induces higher fruit abortion rates. In TOMSIM(1.0) the number of fruits set per truss is not simulated, b ut is an input to the model. TOMSIM(1.0) functions representing flower ing rate, fruit growth period, vegetative sink strength and fruit sink strength were compared with similar TOMGRO(1.0) functions, in their d ependence on temperature and physiological plant age. A sensitivity an alysis was made for the effects of temperature, flowering rate, and fr uit and vegetative sink strengths on dry-matter distribution for both models. A validation of both models was based upon periodic destructiv e harvests in: 1) a greenhouse experiment in Wageningen, using a round tomato cultivar, consisting of a control treatment and a treatment wh ere every second truss was removed at anthesis, and 2) two greenhouse experiments conducted in Montfavet, using a beefsteak. tomato cultivar . Daily shoot dry-weight increase, average 24 h greenhouse temperature s and numbers of fruits set per truss (in TOMGRO(1.0) numbers of flowe rs per truss) were inputs to the models. In general dry-matter distrib ution was simulated well by both models for the cultivar and condition s where they were developed. TOMGRO(1.0)'s poor performance in one of the validations resulted from the absence of an assimilate storage poo l. To achieve reasonable agreement between measurements and simulation s for situations other than where the models were developed, parameter adjustments had to be made, most likely reflecting cultivar differenc es. Strong and weak points of both models are discussed.