AOBPreview published online on February 9, 2008
Annals of Botany, doi:10.1093/aob/mcn007
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Apple Dwarfing Rootstocks and Interstocks Affect the Type of Growth Units Produced during the Annual Growth Cycle: Precocious Transition to Flowering Affects the Composition and Vigour of Annual Shoots
1 The Horticulture and Food Research Institute of New Zealand Ltd, Palmerston North Research Centre, Private Bag 11 030, Palmerston North, New Zealand
2 The Horticulture and Food Research Institute of New Zealand Ltd, Hawke's Bay Research Centre, Private Bag 1401, Havelock North, New Zealand
3 The Horticulture and Food Research Institute of New Zealand Ltd, Mt Albert Research Centre, Private Bag 92 169, Auckland, New Zealand
* For correspondence. E-mail aseleznyova{at}hortresearch.co.nz
Received: 19 September 2007 Returned for revision: 27 November 2007 Accepted: 3 January 2008
Background and Aims: Precocious flowering in apple trees is often associated with a smaller tree size. The hypothesis was tested that floral evocation in axillary buds, induced by dwarfing rootstocks, reduces the vigour of annual shoots developing from these buds compared with shoots developing from vegetative buds.
Methods: The experimental system provided a wide range of possible tree vigour using ‘Royal Gala’ scions and M.9 (dwarfing) and MM.106 (non-dwarfing) as rootstocks and interstocks. Second-year annual shoots were divided into growth units corresponding to periods (flushes) of growth namely, vegetative spur, extension growth unit, uninterrupted growth unit, floral growth unit (bourse) and extended bourse. The differences between the floral and vegetative shoots were quantified by the constituent growth units produced.
Key Results: The dwarfing influence was expressed, firstly, in reduced proportions of shoots that contained at least one extension growth unit and secondly, in reduced proportions of bicyclic shoots (containing two extension growth units) and shoots with an uninterrupted growth unit. In treatments where floral shoots were present, they were markedly less vigorous than vegetative shoots with respect to both measures. In treatments with M.9 rootstock, vegetative and floral shoots produced on average 0·52 and 0·17 extension growth units, compared with 0·77 extension growth units per shoot in the MM.106 rootstock treatment. Remarkably, the number of nodes per extension growth unit was not affected by the rootstock/interstock treatments.
Conclusions: These results showed that rootstocks/interstocks affect the type of growth units produced during the annual growth cycle, reducing the number of extension growth units, thus affecting the composition and vigour of annual shoots. This effect is particularly amplified by the transition to flowering induced by dwarfing rootstocks. The division of annual shoot into growth units will also be useful for measuring and modelling effects of age on apple tree architecture.
Key words: Apple, dwarfing, growth unit, flowering, interstock, Malus x domestica, modelling, plant architecture, polycyclic growth, shoot growth, rootstock