The Influence of Strins and Rootstocks on Photosynthesis, Respiration, and Morphology of ‘Delicious’ Apple Trees1

The performance of young container grown apple trees of two ‘Delicious’ strains was studied under greenhouse conditions in a 2 year experiment. ‘Redspur Delicious’, a spur type strain, and ‘Richared Delicious’ were grown on seedling rootstocks in the first season and on seedling, MM 106, and M VII-A rootstocks the following year. Net photosynthesis (Pn) of ‘Redspur’ leaves tended to be higher than the Pn of ‘Richared’ leaves. One season’s data indicated that the Pn of leaves of greenhouse grown trees on seedling rootstocks was higher than those on MM 106. Leaves of trees on M VII-A were intermediate in Pn. The respiration rates were not affected by strains or rootstocks. Standard2 ‘Delicious’ trees were more vigorous than trees of the spur type as indicated by greater shoot length, internode length, leaf number and total leaf area. The spur type trees had, however, a greater bark-wood ratio. Rootstocks affected both leaf size and leaf dry weight, but strains did not.