Submitted to: International Journal of Fruit Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/2015
Publication Date: 5/1/2015
Citation: Tworkoski, T., Fazio, G. 2015. Effects of size-controlling apple rootstocks on growth, ABA, and hydraulic conductivity of scion of different vigor. International Journal of Fruit Science. doi: 10.1080/15538362.2015.1009973.
Interpretive Summary: Nearly all commercial apple trees are two-part trees; the shoot that assures a specific cultivar is grafted to and grown on; a genetically-different rootstock that controls tree size. We evaluated growth plus two water-use attributes (hydraulic conductivity and the stress-tolerance hormone, abscisic acid, ABA) to identify new apple rootstocks that may adapt to tree management under a variety of environmental conditions including reduced irrigation and drought. It is proposed that shoots grafted to USDA-Cornell developed G.11 and CG.5087 will mature as trees that may be better adapted to dry environments based upon their size and elevated ABA.
Technical Abstract: Size-controlling rootstocks are required to attain trees with reduced stature that are necessary for modern orchard management, such as high density plantings. Apple cultivars can be grafted on commercially-available size-controlling rootstocks but new rootstocks are needed for both size-controlling efficacy and improved tolerance of abiotic and biotic stress. This research was designed to determine the consistency of Geneva and Malling rootstocks for size-control with scions of different growth potentials. Hydraulic conductivity (HC) and abscisic acid (ABA) in xylem exudates were measured in selected scions grafted to Malling (from least-to-most size control M.7, M.9, and M.27) and Geneva (from least-to-most size control, G.935, CG.5087, G.41 and G.11) rootstocks. Regardless of scion vigor, trees with G.935 and G.41 rootstocks had the most height and diameter growth and the highest HC, whereas trees with M.27 rootstocks had the least. Lower ABA was measured in xylem exudate of ‘Fuji’ grown on G.935 and G.41 than CG.5087 and G.11 rootstocks. Regardless of scion vigor, tree growth was less when grown on G.11 and CG.5087 which were associated with less HC and elevated ABA in ‘Fuji' scion. Tree heights of the scion were similar when grown on G.11, CG.5087, and M.7. It is proposed that trees grafted to G.11 and CG.5087 may be better adapted to dry environments based upon their size and elevated ABA.