Volume 52 Number 2 Article 25
Year 1998 Month 4
Title: A Protocol for Rooting and Growing Apple Rootstock Microshoots
Authors: D.K. Isutsa, M.P. Pritts and K.W. Mudge
Abstract:
Microshoots of apple (Malus domestica Borkh.) rootstocks G. 65, G.30 and G.11 were transferred
from stage II axillary shoot cultures to stage III rooting media containing 10 levels of indole-butyric
acid (IBA) for four weeks to determine optimal conditions for rooting.
Microshoots were inverted or
left in an upright position.
Rootstocks and microshoot position affected rooting and survival; the highest rooting was 30% for G.65 inverted with 2 mg L-1 IBA, 100% for G.30 upright with 3 mg L-1 IBA,
and 100% for G.11 inverted with 1 or 2 mg L-1 IBA. No single set of conditions provided consistent
rooting in vitro, and plants were not always of high quality.
In a second experiment, microshoots were
rooted and acclimatized ex vitro in a custom-built fog chamber to assess the effect of two carbon dioxide levels (450 or 1350 µmol mol-1) and three light levels (30, 50 or 100 µmol m-2 s-1). All rootstocks
rooted equally well ex vitro, but survival varied.
Plantlets had the highest dry mass, leaf area and
growth rates under high light conditions compared to medium light or low light conditions.
Supplemental carbon dioxide had no consistent effect.
If plants survived fog chamber conditions, subsequent
survival in the fog tunnel and greenhouse was 100%. Thus, these rootstocks can be rooted successfully in the fog chamber at high light conditions, which yielded high quality plants.
A third experiment
was conducted to evaluate the effect of chilling for four weeks at 3.3°C, or spraying with gibberellic acid 3 (GA3) on post-rooting dormancy, a problem which frequently occurs with recently rooted apple
microshoots.
Chilled plants had greater dry mass than control or GA3 plants, and the GA3 effect was
short-lived.
The ex vitro procedure suggested by these experiments could reduce the time associated
with rootstock micropropagation to at most 6 months.
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