Abstract
This study investigated how leaf net photosynthesis and growth of trees of ‘New Jonagold’ apple (Malus domestica Borkh.) trees vary according to rootstocks: JM1, JM7 and JM8 (M. prunifolia Borkh. var. ringo Asami × M. pumila Mill. var. paradisiaca Schneid.), and virus-free M.9 (M. pumila Mill. var. paradisiaca Schneid). The results of the experiment showed that on detached and watered shoots, there were no significant differences among the four rootstocks in the photosynthesis and transpiration rates. In contrast, the photosynthesis and transpiration rates and leaf stomatal conductance for JM1 exhibited significantly lower levels than JM7, JM8 and virus-free M.9 on field-grown trees, although a midday depression occurred for all of the rootstocks. Regarding the growth of trees, the results demonstrated that the trees grafted on JM7 and JM8 grew significantly bigger than those on virus-free M.9, while trees on JM1 demonstrated significantly less growth. These findings suggest that certain rootstocks have an observable effect on the degree of midday depression of leaf photosynthesis depending on drought stress conditions. These findings also imply that apple trees grafted onto JM1 are substantially dwarfed since the JM1 rootstock is subject to greater midday depression in leaf photosynthesis.
