Submitted to: International Symposium on Integrating Canopy, Rootstock and Environmental
Publication Type: Abstract Only
Publication Acceptance Date: May 12, 2008
Publication Date: August 3, 2008
Citation: Tworkoski, T., Fazio, G. 2008. Physiological and morphological effects of size-controlling rootstocks on 'Fuji' scion. International Symposium on Integrating Canopy, Rootstock and Environmental Physiology in Orchard Systems in Geneva, NY, August 4-8, 2008. Technical Abstract: The size-controlling effects of apple rootstocks were partially characterized in greenhouse experiments. Two-year-old 'Fuji' scions on 25 size-controlling rootstocks, from the USDA apple rootstock breeding program in Geneva, NY, were grown for one season and shoot development was measured each month. Discriminant analysis associated the rootstocks into three clusters based on similarity of shoot secondary and primary growth and tree height. Total shoot growth for one season was 367, 283, and 149 cm for rootstock cluster (RC) A, B, and C, respectively. RC-A had significantly greater photosynthesis and transpiration rates than RC-C (18.3 and 12.3 umol CO2 / m-2 leaf area / sec(-1) and 4.2 and 3.1 mmol H2O / m(-2)leaf area / sec(-1), respectively). At the end of the first growing season, trees were placed in controlled cold environments to provide chilling. At the beginning of the second growing season, trees were removed from chilling, the roots were pressurized, shoots were removed 40 cm above the graft union, and hydraulic conductivity was measured. Xylem exudate was collected and analyzed for cytokinin (CK), abscisic acid (ABA), and inole-3-acetic acid (IAA). Less hydraulic conductance was associated with the more dwarfing rootstocks, RC-C, compared with the more invigorating RC-A (0.58 and 1.41 mL / cmStem(-1) / hr(-1)/ MPaLeaf-1, respectively). Abscisic acid flux was higher in xylem exudates from dwarfing (RC-C) than vigorous (RC-A) rootstocks (2.28 and 0.23 pmol / mL-1 / hr-1, respectively). The concentrations of CK and IAA were variable and rootstock-related differences were not determined. Stem samples of scion and rootstock from above and below the graft were collected and anatomical differences of stem cross-sections are being analyzed with scanning electron microscopy. Initial results show that fiber wall thickness in late wood was greater in 'Fuji' scion on RC-C than RC-B and RC-A rootstocks. The data indicate that chemical signals, such as hormones, as well as hydraulic signals, may play a role in size-controlling processes of apple rootstocks.