ISHS Acta Horticulturae 160: III International Symposium on Research and Development on Orchard and Plantation Systems
GRAFT-UNION CHARACTERISTICS AS RELATED TO DWARFING IN APPLE (MALUS DOMESTICA BORKH.) |
| Author: | R.K. Simons |
| Abstract:
Development of the graft-union in apple dwarfing stock/scion combinations showed abnormal morphological characteristics associated with the different degrees of dwarfing. The effect of regenerative growth of wound tissues between the stock and scion may be determined microscopically during the first year's growth after budding. Thickening of the outer bark was apparent on Malling 9 (M.9), Malling 26 (M.26) and Malling 27 (M.27) rootstocks when combined with Granny Smith. The restrictive influence upon the vascular tissues within the graft-union area was continued with successive periods of tree growth. The vascular system of extremely dwarfing rootstocks was characterized as: 1) the major portion of the phloem contained large areas that were non-functioning; 2) regenerative tissues developed into swirling patterns by which the vascular tissues became abnormally constricted and oriented at a right angle to the normal, longitudinal pattern of growth; 3) senescence of vascular tissues accentuated the swirling formation of regenerative phellogen that became necrotic, and thus perpetuated necrosis within this vital area; and 4) sinks of calcium-containing crystals were found contiguous to senescing and/or necrotic areas in the functioning phloem adjacent to the cambium. | |
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