Changes in photosynthetic and other yield components contributing to yield improvement of Dutch tomato.

MSc-thesis abstract (submitted 4 June 2015):
Dutch greenhouse tomato (Solanum lycopersicum) yield continuously improves due to favourable growth conditions and breeding. Changes in leaf photosynthesis and light extinction coefficient (k) in modern cultivars were proposed to underlie this improvement.

To validate this conclusion, yield and photosynthetic components of six round tomato cultivars, released between 1975 and 2013, were analysed in a greenhouse experiment from June to December in 2014 at Wageningen University, The Netherlands. An increase in yield of 1 % per year with the year of release was mainly caused by a decrease in fruit dry matter content of 0.03% per year. Total fruit dry weight and total aboveground dry matter increased with the year of release. Canopy light interception and light use efficiency improved with the year of release because of higher leaf area index, reduced k, and enhanced leaf photosynthetic rate in modern cultivars. Reduced k was characterized by an increase in internode length.

Higher leaf photosynthesis was observed in both top and middle leaf layer. Photosynthetic capacity increased 0.4 % per year and was positively correlated with leaf chlorophyll content and light absorptance. In conclusion, modern cultivars possess characteristics which make them capable to maintain high long-term productivity with current greenhouse technology.

Keywords: Breeding, Yield component, Dry matter production, Dry matter partitioning, Leaf area index, Light use efficiency, Light interception, Light extinction coefficient, Photosynthesis, Chlorophyll, Light absorptance