Agriculture Reference
In-Depth Information
rootingevenwithauxintreatment,andreductionoftheleafareatoonequarter
had a major negative effect, but bud removal had no apparent effect.
Howard (
) concluded that the negative effect of disbudding on the
rooting of leafless winter cuttings of apple was primarily due to desiccation
through disbudding wounds.
The need for leaves on summer but not winter cuttings may reflect differ-
ences in carbohydrate reserves.
All growth requires energy. A carbohydrate source, usually sucrose, is an essen-
tial constituent of tissue-culture media and the regeneration potential and sur-
vival rate of root cuttings is highest if they are taken at the time of maximum ac-
cumulated reserves of storage polysaccharides (Robinson and Schwabe,
).
Summer cuttings (see above) require the presence of leaves to root even if
auxin is supplied. Leafless winter cuttings are much larger and have the ben-
efit of carbohydrate exported from the leaves during and at the end of the
growing season. Their ability to root is not necessarily related to initial dif-
ferences in carbohydrate content. Rooting and subsequent establishment of
these cuttings may, however, be reduced by factors such as high temperatures
and bud growth which lead to increased respirational losses of carbohydrate
or to its redistribution away from the rooting zone (Cheffins and Howard,
a,b).
!
Auxins, co-factors and inhibitors
Following work on other plants which showed that auxin was involved in
adventitiousrootformation,PearseandGarner(
)foundthatimmersionof
thebasesofsoftwood(leafy)cuttingsof
Pyrus communis
rootstockin
ppmNAA
(naphthaleneacetic acid) for
hours was very effective in inducing rooting.
The control cuttings did not root and many subsequent studies have shown
synthetic auxins to be effective in inducing rooting of cuttings which would
not otherwise do so. IBA (indolebutyric acid) and NAA are more effective than
the naturally-occurring indoleacetic acid (IAA). IBA is now generally used to
root apple and pear cuttings, being preferred to NAA because of its ability
to induce a fibrous root system and not to translocate in the stem and inhibit
bud growth to the same extent as NAA (Howard,
). IBA is applied to the
bases of cuttings as the acid dissolved in ethanol or acetone, as the potassium
salt dissolved in water, or as a powder formulation. In the United Kingdom a
'quick dip' of the base of the cutting for
seconds to a depth of
cm in
ppm IBA in a
% aqueous solution of acetone is routinely used for the apple
rootstocks 'M.
', 'MM.
' and 'M.
' (although only a small proportion
