PHOTOSYNTHESIS, ¹⁴C-PHOTOSYNTHATE DISTRIBUTION AND SHOOT AND ROOT GROWTH OF YOUNG APPLE TREES ON 3 ROOTSTOCKS EXPOSED TO FLOODING

Photosynthesis and ¹⁴C-photosynthate distribution, root growth dynamics, shoot extension, leaf number and TCAI were monitored for ‘Jonnee’ apple on M.9 EMLA, M.26 EMLA and Mark rootstocks that were subjected to 2, 4, 8, 16 and 32 days of flooding. Stress was imposed for all flooding durations on the same date. Recovery was monitored until 45 days after the 32 day flooding stress. Photosynthetic response to flooding varied by rootstock and flooding duration. Distribution of ¹⁴C-photosynthates between the root and shoot system was affected for M.26 EMLA and Mark rootstocks. No differences were seen in root dynamics until 32 days of continuous flooding. From day 32 until termination of the experiment, fewer roots were produced for 32 day flooded M.9 EMLA and M.26 EMLA. There were fewer roots produced for 32 day flooded Mark on day 32 but root production was similar to controls during recovery. Shoot growth and TCAI were reduced substantially for all flooded rootstocks. The number of leaves decreased as flooding duration increased.