EVALUATION OF TOMGRO, A DYNAMIC-MODEL OF GROWTH AND DEVELOPMENT OF TOMATO (LYCOPERSICON-ESCULENTUM MILL) AT VARIOUS LEVELS OF ASSIMILATE SUPPLY-AND-DEMAND

TOMGRO, a tomato growth and development model, has been examined under different levels of assimilate source and sink activities, induced by CO2 enrichment and truss thinning. The main purpose was the evaluatio n of the assumptions on dry matter partitioning and fruit setting. The photosynthesis submodel has been calibrated to fit the daily dry matt er production. The main input parameters to the development and growth submodels have been experimentally measured. The calibrated model pro vides good simulations of the leaf area expansion, but it takes no acc ount of the variations in the assimilates stored in leaf blades. Total fruit growth is well simulated in spite of a small underestimation fo r of development and simulations of source/sink balance leads to good simulations of the number of set fruits. This result confirms the hypo thesis that fruit set depends on the ratio between assimilate source a nd sink activities. This calibration with a beef tomato cultivar prove s the robustness of the model and permits some improvements to be sugg ested. The surplus assimilates should be stored in a pool, which could exert a buffer effect during low supply periods. Sink strength of rep roductive and vegetative parts should be measured for different cultiv ars, and under various climatic conditions. Finally, whether the funct ions of assimilate distribution and fruit set are still valid under ve ry low supply conditions or whether some organs have priority over the others remains to be determined.