Yield and Dry Matter Production of a Japanese Tomato ‘Momotaro York’ Are Improved by Grafting onto a Dutch Rootstock ‘Maxifort’

To improve the yield of a Japanese tomato (Solanum lycopersicum) cultivar and determine how fruit yield changes as a result of grafting, we investigated the effects of a Dutch rootstock [‘Maxifort’ (S. lycopersicum × S. habrochaites): Mx] on the dry matter (DM) production and fruit yield of Dutch and Japanese cultivars. The Japanese cultivar (‘Momotaro York’: My) grafted onto Mx (My/Mx: scion/rootstock) had significantly higher fresh and dry weights of fruits per unit area than My/My. Fruit fresh weight yield per unit area was highly correlated with fruit dry weight (DW) yield (r = 0.96–0.97, P < 0.001), and DW yield was significantly correlated with total aboveground DM (r = 0.71–0.96, P < 0.001) and with DM allocation to the fruits (r = 0.52–0.75, P < 0.01). Total aboveground DM (TDM) was significantly and highly correlated with light-use efficiency (r = 0.98, P < 0.001). However, there was no significant correlation between light-use efficiency and the maximum photosynthetic rate, stomatal conductance, or the light-extinction coefficient. Although stomatal conductance significantly (P < 0.05) differed between the rootstocks at 57 and 119 days after transplanting (DAT), there was no significant difference in the maximum photosynthetic rate between the scion/rootstock combinations at 57 and 119 DAT. These results indicated that the fruit yield of My could be improved by grafting onto Mx, and that the increases in yield and TDM were mainly determined by the increase in light-use efficiency.