Agriculture Reference
In-Depth Information
in a glasshouse. Alternatively, shoots from
in vitro
culture can be rooted directly
in potting compost after being dipped in IBA powder.
Mass propagation of apple and pear rootstocks
in vitro
is, at present,
relatively expensive compared with conventional vegetative propagation.
It may play an important role in the rapid multiplication of new root-
stock cultivars and their distribution in disease-free form, but under some
circumstances
in-vitro
-produced rootstocks if used directly produce exces-
sive numbers of burr-knots and suckers, possibly associated with enhanced
juvenility.
Sequential shoot subculture may greatly increase the readiness with
which the shoots root. This is apparently due to tissue rejuvenation (i.e.
development of juvenile characteristics including ready-rooting, but also
spinyness and slowness to bear fruit) and provides a means of increasing
the rooting potential of normally difficult-to-root but otherwise desirable
rootstocks.
The apparent rejuvenation that takes place
in vitro
persists following estab-
lishment of nursery hedges, and both winter and summer cuttings from such
hedgesof'M.
'showimprovedrooting.Stoolbedsestablishedfrommicroprop-
agated (
in-vitro
-cultured) plants of 'M.
times
as many shoots as their conventional counterparts and these shoots are better
rooted ( Jones,
' produce between
.
and
.
). Conventional cuttings from micropropagated plants of
a very difficult-to-propagate
Pyrus communis
rootstock show greatly improved
rooting ( Jones and Webster,
). Scion cultivars which are difficult to root
as cuttings can readily be produced on their own roots by
in vitro
culture. Some
cultivarswhicharenaturallycompactandprecociousinfloweringappeartobe
satisfactory when self-rooted via
in vitro
culture, but in general self-rooted cul-
tivars are too vigorous and are slower to come into crop than when grafted on
precocity-inducing rootstocks (Webster
et al.
,
; Zimmerman and Steffens,
).
Leaf discs and leaf strips produce shoots
in vitro
whengrownonanMS
(Murashige & Skoog) basal medium supplemented with
mg BA l
−
and
.
mg NAA l
−
( James
et al.
,
). This is particularly important because leaf
mesophyll cells are competent for transformation, i.e. the insertion of 'foreign'
genes. An N
.
-based medium may also be used for leaf disc culture (Welander,
).
Regeneration systems for
Malus
have been developed from a wide range
of other explants including embryo, nucellus, cotyledon, hypocotyl, immature
seed, flower part, and anther tissues (Korban and Chen,
).
Somaclonal variation may express itself as a result of
in vitro
culture. Much
of this variation reveals deleterious traits but some, e.g. in fireblight resistance
(Chevreau
et al.
,
), is potentially useful.
