Title: Physiological processes of size-controlling rootstocks in apple Authors
Submitted to: Annual Cumberland Shenandoah Fruit Workers Conference
Publication Type: Proceedings
Publication Acceptance Date: December 20, 2011
Publication Date: May 23, 2012
Citation: Tworkoski, T., Fazio, G. 2012. Physiological processes of size-controlling rootstocks in apple. In: Proceedings of the 87th Annual Cumberland-Shenandoah Fruit Workers Conference, December 1-2,2011, Winchester, VA. p. 11. Technical Abstract: Small, efficient trees are critical for early and high yield in high-density plantings of apple. Tree size is controlled by budding scion to size-controlling rootstocks. New rootstocks are needed for both size-controlling efficacy and tolerance of abiotic and biotic stress. Improved knowledge of rootstock-related processes associated with size-control can be an important factor in rootstock breeding. This research was designed to determine the consistency of Geneva and Malling rootstocks for size-control of a variety of scions. Associated with growth, hormone concentrations were examined in xylem exudates from dwarfing and vigorous roots. Buds from a variety of apple trees, including ‘Gala’ and ‘Fuji’ were grafted to selected rootstocks (G.11, G.935, G.41, G.5087, M.7, M.9, M.27, MM.111) in 2009, and then grown in a greenhouse or the field. Shoot growth, bud break, and flowering were measured during 2010 and 2011. A subset of trees was evaluated for hormone concentration in xylem exudate after one month of growth in 2011. In the greenhouse, each rootstock had similar relative effects on shoot growth of various scions. For example, one year after budding, ‘Gala’ and ‘Fuji’ shoot growth was generally 20 to 30 percent less than control on M.9 (dwarfing) than MM.111 (more vigorous). Growth control by rootstocks in the field was similar but less consistent than in the greenhouse. The combination of abscisic acid (ABA) and ABA metabolites were greater in xylem exudate of M.9 than MM.111. Gibberellins (GA) and auxins (IAA) were found in exudate of MM.111 but not M.9. These results indicate that several hormones that move within tree xylem may be important factors associated with size controlling rootstocks.