Fruit growth and dry matter partitioning in cucumber

In this thesis, dry matter partitioning into different plant parts of generative cucumber plants was quantitatively studied as a dynamic process in terms of an internal competition among organs for assimilates in relation to external factors, such as the greenhouse climate and cultural practices. As the fruits represent the major sink organs and as they are of economic interest, special attention was paid to the growth and development of the individual fruits.During a growing season the fraction of dry matter partitioned into the fruits changed cyclically between 40 and 90%. Dry matter partitioning appeared to be primarily regulated by the sinks (fruits). Source strength influenced the number of fruits on a plant and, therefore, indirectly influenced the dry matter partitioning, although after a lag phase. No feed-back effect of the number of fruits per plant on source strength (leaf photosynthesis) was observed, unless all fruits were removed for a prolonged period.The growth rate of an individual fruit, but not its development, was strongly dependent of the assimilate supply. Fruit development appeared to be closely related to the temperature sum. The growth rate increased with increasing temperature, but the effect on final fruit weight depended on the level of assimilate supply. Irradiance affected growth of individual fruits via effects on assimilate supply, but had no photomorphogenetic effect. During fruit ontogeny, cells expanded continuously, but cell division was restricted to the first part of the growing period. Although usually the size of the cucumber fruit positively correlated with the number of cells, cell number was not an important determinant of fruit size.Fruit photosynthesis contributed only to a small extent (1-5%) to the cumulative carbon requirement of a fruit. Thirteen to 15% of the cumulative carbon requirement of a fruit was respired. The respiratory losses as a fraction of the carbon requirement of a fruit changed during fruit ontogeny, but were independent of temperature and were similar for slow and fast growing fruits.A dynamic model was developed for the simulation of the daily dry matter partitioning. In the model dry matter partitioning was simulated as a function of sink strengths of the plant organs, where sink strength of an organ was described by its potential growth rate. Model results agreed well with the measured data.