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 × domestica, modelling, plant architecture, polycyclic growth, shoot growth, rootstock Go to:
Plant architecture is a relatively new and rapidly developing scientific discipline that provides powerful tools for analysis of plant structure and ontogeny (Hallé et al., 1978; Barthélémy and Caraglio, 2007). Architectural analysis is based on the hypothesis that plant structures are ‘built’ by the addition of similar constructional units (White, 1979; Barlow, 1994). The number of different construction units is relatively small and corresponds to different nested levels of organization. The basic elementary building block of plant structure is a metamer comprising a node, a leaf (or leaves), axillary bud(s) and a subtending internode (White, 1979). In a process of growth, addition of metamers builds a leafy axis. Axis extension can be continuous or rhythmic; the latter occurs in successive growth flushes (or cycles) interrupted by periods of rest, resulting in the morphologically distinct growth increments referred to as growth units (Hallé and Martin, 1968; Reffye et al., 1991). Each growth unit may have a ring of bud scales, bud scale scars and/or a zone of short internodes at its base that morphologically marks a period of rest (Barthélémy and Caraglio, 2007). In some temperate species axis extension may occur in one or more successive events during the same growing season, forming an annual shoot consisting of one or more successive growth units or growth cycles. When two or more growth units are formed during the same season they are often not identical but have distinctive features (Kozlowski, 1971). In such cases, the annual shoot level of organization is particularly useful for representation of the plant structure. It is well documented that during plant growth and branching, the repeated botanical entities such...
Please join StudyMode to read the full document