The Expression of Acrotony in Deciduous Fruit Trees: A Study of the Apple Rootstock M.9

Abstract

<jats:p>One-year-old shoots of apple (<jats:italic>Malus ×domestica</jats:italic> Borkh.) rootstock Malling 9 (M.9 clone Nic 29), ≈60 cm long without sylleptic side shoots, were selected randomly from a commercial stoolbed in Belgium, prepared, and forced at 25 °C and 16 hours daylength to follow bud developmental rate in different positions along a 1-year-old shoot. The number of buds that reached green tip was recorded daily until 50% of shoots exhibited budburst. The evolution of dormancy of the terminal, an upper lateral, and a lower lateral bud was followed throughout the dormant period. The influence of a distal disbudded shoot piece and Promalin [3000 mg·L<jats:sup>-1</jats:sup> <jats:italic>N</jats:italic>-(phenylmethyl)-1<jats:italic>H</jats:italic>-purine 6-amine and 3000 mg·L<jats:sup>-1</jats:sup> gibberellins A<jats:sub>4</jats:sub>+A<jats:sub>7</jats:sub> without a wetting agent] application on the developmental rate of these buds was evaluated. Bud developmental rate decreased during winter and increased to a maximum before budburst in spring. The distal shoot-forming ability or acrotonic branching habit in apple appears to be mediated via a greatly increased developmental rate of the terminal bud relative to the upper and lower lateral buds, respectively. The proximal budbursting tendency or basitony exhibited in early winter was weak compared to the acrotony that developed in the last month before budburst in spring. Lateral buds showed a lower developmental rate than the terminals when inhibited by a distal disbudded shoot piece, so that resultant overall growth habit within the shoot remained acrotonic throughout the dormant period. Promalin application in winter did not restore the bud developmental rate associated with spring budburst. These results are discussed with reference to observations of trees growing under conditions of insufficient winter chilling.</jats:p>

Environment and position of first bud to break on apple shoots affects lateral outgrowth

“…Depth of dormancy and dormancy progression has been shown to differ among locations and cultivars (Cook and Jacobs 2000), as well as among bud types and position within the axis (Cook and Bellstedt 2001;Jacobs et al 1981; Mauget and Rageau 1988). Terminal and lateral buds also differ in their progression through dormancy (Cook et al 1998;Cook and Jacobs 1999;Mauget and Rageau 1988;Williams et al 1979). Terminal buds are characterized by a rapid entrance into dormancy in autumn followed by an exit from dormancy that is initially slow, becoming rapid just before budbreak in spring (Cook et al 1998).…”

“…Terminal and lateral buds also differ in their progression through dormancy (Cook et al 1998;Cook and Jacobs 1999;Mauget and Rageau 1988;Williams et al 1979). Terminal buds are characterized by a rapid entrance into dormancy in autumn followed by an exit from dormancy that is initially slow, becoming rapid just before budbreak in spring (Cook et al 1998). This is altered when chilling is insufficient.…”

“…Acrotony exists on a number of levels (acropetal increases in organogenesis, budbreak time and location, lateral outgrowth, and fruit-set) (Barthélémy and Caraglio 2007;Cook et al 1998;Costes and Guédon 2002;Lauri 2007).…”

“…The decrease in or absence of lateral budbreak has been attributed to the primigenic dominance of the terminal (Saure 1985;Faust et al 1995;Williams et al 1979), as well as distally-located lateral buds (Jacobs et al 1981). However, sufficiently chilled areas also have primigenic dominance of the terminal, and this does not restrict budbreak (Cook et al 1998). In addition, apple genotypes have different levels of apical control as evidenced by their differing degrees of acrotony (De Wit et al 2000Lauri 2007).…”

Are the effects of winter temperatures on spring budburst mediated by the bud water status or related to a whole-shoot effect? Insights in the apple tree

“…Dormancy is the temporary suspension of visible growth of any plant structure containing a meristem (Lang et al 1987) and plays a key role in budburst and branching patterns (Cook et al 1998). Each individual bud has its own physiological state which depends both on its endogenous ability to burst and on its position within the shoot (e.g., proximal or distal part) and tree canopy (e.g., on a short or on a long shoot), and which determines its growing potential (Mauget and Rageau 1988).…”