|Authors: ||B.M. van Hooijdonk, D.S. Tustin, M.J. Oliver, G.A. Dayatilake|
|Keywords: ||Malus × domestica, vigour, roots, shoots, dry weight|
Total seasonal dry matter production of apple trees is positively correlated with total seasonal intercepted solar radiation.
This fundamental principle has application in maximising dry matter accumulation of newly propagated apple trees, necessary for rapid establishment of orchard canopies.
We hypothesise that for newly grafted trees grown with non-limiting water and nutrients, seasonal dry matter production may be limited by the rate of primary axis leaf area development, which could be modified by tree design, date of grafting and the type of scion bud grafted.
Newly grafted apple trees on LSQUOMalling 9RSQUO were grown with either one (monoaxis) or two (biaxis) primary axes to elucidate how increasing shoot number per tree modified leaf area development, dry matter production and its allocation.
At 52 days after budbreak (DABB), the total primary axis node number and leaf area of biaxis trees was 22 nodes tree-1 and 0.05 m2, respectively, approximately twice that of monoaxis trees (11 nodes tree-1 and 0.02 m2). At autumn growth cessation (246 DABB), the total primary axis node number of biaxis trees was 132 compared with 71 for monoaxis trees; their corresponding total primary axis leaf areas were 0.9 and 0.5 m2. The final total leaf area tree-1, however, was similar because of greater sylleptic shoot development on monoaxis trees throughout summer.
The final total tree dry weight was 18% higher for biaxis than monoaxis trees, with biaxis trees showing increased dry weight of both root and scion.
In two further experiments, trees produced by grafting bud wood with mixed floral buds developed ≈30% less final total tree dry weight compared with trees produced by grafting bud wood with vegetative buds.
Delaying winter grafting from the first to the last week of August (late winter) reduced scion dry weight by ≈20%. We conclude that growth of newly grafted trees is limited by early season leaf area development.
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