Agriculture Reference
In-Depth Information
of these rootstocks are propagated by winter cuttings). A concentration of
ppm is used for quince rootstocks if they do not bear pre-formed roots
(Howard,
).
Treatment with IBA of the roots of dormant pear trees in the nursery prior
to planting out can lead to increased root production after this (Looney and
McIntosh,
).
Divisions of the first root initial cells of a range of plants have been shown to
be dependent on either applied or endogenous auxin (Hartmann
et al.
,
).
The process of root elongation which follows initiation is either insensitive to,
or inhibited by, auxin. James (
) showed that the auxin-sensitive phase for
apple cuttings
in vitro
lasts for only
days, during which time root initiation is
very sensitive to incident light.
The effect of auxin on rooting is generally enhanced by the action of rooting
co-factors (Hess,
). These have been studied in both
in vitro
(micropropa-
gation) and large cutting (macropropagation) systems.
JonesandHatfield(
)showedthatphloroglucinol,aphenoliccompound,
and auxin together induce rooting of apple rootstocks
in vitro
, and James and
Thurbon (
) found that phloroglucinol acted as an auxin synergist in root
initiation in 'M.
' apple rootstock shoot cultures over a range of concentrations
mg l
−
.
Challenger
et al.
(
from
.
to
) used the mung bean bioassay to find rooting co-
factors in 'Crab C' and 'M.
' apple rootstocks, and Ashiru and Carlson
(
) found strong root promoting factors in the easy-to-root 'MM.
', and
lower amounts, and also rooting inhibitors, in the difficult-to-root 'M.
'. Fadl
and Hartmann (
a, b) isolated an endogenous root promoting factor in
basal sections of the easy-to-root 'Old Home' pear cultivar cuttings after IBA
treatment but not in similar cuttings of the difficult-to-root 'Bartlett' cultivar.
This rooting factor was possibly a condensation product of the applied auxin
and a phenolic substance produced by the buds. Bassuk
et al.
(
) showed
a positive correlation between endogenous root-inducing co-factor activity in
sap and seasonal changes in rooting of 'M.
' winter cuttings and Bassuk
et al.
(
) found an apparent involvement of polyphenol oxidase and phloridzin
in the production of apple rooting co-factors.
Cytokinins
Although in general cytokinins are inhibitory to adventitious root formation
(McCown,
), they may have a positive indirect effect through rejuvenation
by repeated subculturing
in vitro
(Sriskandarajah
et al.
,
).
Gibberellins
Takeno
et al.
(
) found a negative relationship between endogenous gib-
berellin level and the
in vitro
rooting ability of
Malus
.
