Investigation of carbohydrate concentration and leaf photosynthesis during plant development of three tomato cultivars.

MSc-thesis abstract (submitted 8 August 2014):
Tomato is grown in the greenhouse and produced year–around in the Netherlands. In winter, supplementary light is applied in the greenhouse to compensate for low natural radiation. However, simulations showed that a surplus carbohydrates accumulated in leaves during vegetative and early reproductive phases of tomato plants. Furthermore, ‘feedback inhibition’ caused by carbohydrate accumulation was proposed by many researchers. In that case, application of supplementary light is not economical efficient.

The aims of this research was to investigate whether sink-limited situation of tomato plants occurred in vegetative and early reproductive phases, and if this sink-limitation influenced by cultivars with different potential fruit sizes and fruit pruning.
In addition, if sink-limitation occurred, whether accumulated carbohydrates could down-regulate photosynthetic rate or not.

Sink strength of tomato plants was manipulated by three cultivars (Solanum lycopersicum, cv. ‘Sunstream’, ‘Cappricia’ and ‘Komeett’) and fruit pruning treatment. The total growth period was from 16th August 2013 to 22th of November 2013. Supplementary light was applied from 6:00h to 16:00h since 17th September 2013. Periodic destructive measurements were conducted. Starch was the main carbohydrate in leaves, while total soluble sugar (especially glucose) was the main carbohydrate in stems. Starch concentration in canopy-leaves was always higher at sunset compared to sunrise. Starch concentration in top-leaf was higher than that of canopy-leaves at both sunrise and sunset. Carbohydrate were accumulated in the vegetative or early reproductive phase. Total soluble sugar concentration in stems correlated negatively with the potential fruit size, while starch concentration in stems not well correlated with the potential fruit size. The stored soluble sugar in stems could be remobilized to fruit. Potential fruit size did not well correlate with carbohydrate concentration and photosynthetic rate in leaves. ‘Cappricia’ with medium fruit size had the highest leaf carbohydrate concentration in leaves. Half pruning had no influence on carbohydrate as well as photosynthesis in leaves. Total dry weight was not influenced by fruit pruning, whereas, dry weight partitioning to stems, leaves and fruit was significantly affected. Pruning led to heavier stems and higher average fruit weight.