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Tadahisa Higashide

Effects of solar radiation and temperature in different periods before and after anthesis on yield of tomato (Solanum lycopersicum) in summer greenhouse cultivation were investigated. Fluctuations in yield were caused mainly by the variation in fruit number rather than fruit weight. The number of harvested fruit and the yield of plants grown in summer and fall were significantly and positively correlated with solar radiation during the days before anthesis. Although the fruit number and yield were also significantly correlated with air temperature before anthesis, the correlations were weaker than the correlations with solar radiation. There was no significant correlation between the air temperature in the periods encompassing 3 weeks before harvesting and the fruit number and yield. Therefore, fluctuations in fruit number and yield could be predicted by a model based on the solar radiation from 10 to 4 days before anthesis. Validation based on data sets independent of the one used to develop this model showed good correlations between observed and predicted results for plants grown in summer and fall. Thus, solar radiation before anthesis was one of the important factors in prediction of tomato yield under warm greenhouse conditions.

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Tadahisa Higashide and Ep Heuvelink

Greenhouse tomato (Solanum lycopersicum) yield in The Netherlands has increased tremendously over the past 50 years. The effects of breeding during this period were investigated. Eight Dutch cultivars and one typical current Japanese cultivar that were released over the past 50 years were compared in a short-term experiment conducted from summer to fall in The Netherlands. Fresh fruit yield of the Dutch cultivars significantly increased ≈0.9% per year with the year of release from 1950 to 2000. Dry weight fruit yield of the Dutch cultivars also increased with the year of release, whereas the fruit dry matter content was not correlated with the year of release. Total dry matter production of plants increased with the year of release, and the dry matter partitioning to fruit was not correlated with the year of release. An increase in dry matter production was caused not by an increase in fraction of intercepted light, but by light use efficiency based on correlations between each of them and the year of release. The light extinction coefficient in the plant canopy decreased, whereas leaf photosynthetic rate increased significantly with the year of release. Although fresh fruit yield of the Japanese cultivar was lower than that of the modern Dutch cultivars, fruit dry matter content of the Japanese cultivar was higher than that of the Dutch cultivars. An increase in yield over the past 50 years in Dutch tomato was caused by an increase in light use efficiency resulting from a decrease in light extinction coefficient (a morphological change) and an increase in leaf photosynthetic rate (a physiological change).

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Tadahisa Higashide, Ken-ichiro Yasuba, Katsumi Suzuki, Akimasa Nakano, and Hiromi Ohmori

The yield of greenhouse tomatoes in Japan has not increased since the 1980s and remains much less than 30 kg·m−2 per year. To investigate the cause of this low yield, we compared six Japanese tomato cultivars that were commonly grown or released during the past 80 years to see whether fruit yield (fruit fresh weight per area) and dry matter (DM) content per fruit improved under current cultivation conditions. Fruit yield in ‘Momotaro’ (released in 1985) was lower than that in older cultivars. Total DM was determined mainly by light use efficiency and photosynthetic rate, and light use efficiency was correlated with maximum photosynthetic rate. The more modern cultivars did not show improved DM content per fruit. The DM content per fruit was strongly correlated with the soluble solids content in fruits except in ‘Momotaro’ and ‘Momotaro colt’, but soluble solids in fruits of the ‘Momotaro’-type cultivars were higher than in other cultivars for a given DM content per fruit. Thus, tomato breeding in Japan appears to have focused on fruit soluble solids content per unit DM rather than fruit yield or DM content; as a result, only the former parameter has improved greatly.

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Tadahisa Higashide, Yuya Mochizuki, Takeshi Saito, Yasushi Kawasaki, Dong-Hyuk Ahn, and Akio Ohyama

To investigate the influence of morphological changes in individual leaves of tomato on light interception and dry matter (DM) production, we altered leaf shape by trimming leaflets of young or mature leaves of the Dutch cultivar Gourmet and the Japanese cultivar Momotaro York. Young leaves 5-cm long were trimmed of their first and second leaflets from the leaf apex. Mature leaves were similarly trimmed at ≥71 days after transplanting (DAT). The individual leaf area (LA) of intact ‘Momotaro York’ leaves was significantly larger than that of ‘Gourmet’. Light–photosynthesis curves of the cultivars were almost identical. Mature-trimmed plants of both cultivars had a smaller individual LA and a smaller leaf area index (LAI), and a greater light-extinction coefficient (LEC). Although there was no significant difference in light-use efficiency (LUE) (i.e., DM production per unit intercepted solar radiation) in ‘Gourmet’ between trimming stages, LUE of ‘Momotaro York’ was decreased significantly by young-leaf trimming. Trimming of young leaves significantly decreased the LEC in ‘Gourmet’ but increased it in ‘Momotaro York’. Although leaf trimming would be impractical for commercial cultivation, these results may provide with a clue for breeding for yield improvement.