Photosynthetic Rates in Leaves of ‘Hiratanenashi’ Persimmon Trees on ‘MKR1’ Dwarfing Rootstock, and Vigorating Rootstocks, as well as Own-rooted Trees

The photosynthetic rates of ‘Hiratanenashi’ trees (Diospyros kaki Thunb.) grafted on a dwarfing rootstock, ‘MKR1’, and vigorating rootstocks, D. kaki seedling and rootstock a, as well as own-rooted trees, which were established in an orchard in March 2003, were measured at several times on May 2, May 6, July 11, August 6, August 15, and September 26, 2013. The photosynthetic rates at each time on each measurement date were not significantly different among the trees, except for that at 14:00 on May 6. Hence, the photosynthetic rate was not considered to cause the trees grafted on ‘MKR1’ to show dwarfism. The daytime reduction of the photosynthetic rate occurred in all types of tree when the photosynthesis active radiation exceeded 2000 μmol・m−2・s−1, and this phenomenon was thought to be an effect of photoinhibition. The photosynthetic rate of the trees on ‘MKR1’ decreased markedly at 14:00 on May 6, being the greatest daytime reduction among all types of tree. A reason that the leaves of trees on ‘MKR1’ showed the photoinhibition more readily may be that the dwarfed trees had fewer, smaller leaves, and so they received stronger sunlight par unit area.