Agriculture Reference
In-Depth Information
included crosses with
M. baccata
(L.) Borkh,
M.
×
floribunda
, 'Antonovka',
×
×
M.
robusta
and others to introduce resistance to low tem-
peratures, apple scab, apple mildew and woolly aphid. Rootstocks from this
programme are available as the Pillnitzer 'Supporter' series (Fischer,
micromalus
,
M.
).
Jork research station, also in Germany, produced 'Jork
' ('J.
') from seed from
open-pollinated 'M.
'.
Selection of sub-clones of rootstock cultivars
In common with the scion cultivars the rootstock cultivars of
Malus
, although
clonal, show an appreciable degree of variability and mutability (Baumann,
). This is demonstrated in two main
ways. First, either nurserymen have selected within their stocks, especially of
'M.
; Engel,
,
; van Oosten,
', or their standard clones have been found to differ from those in other
nurseries. Secondly, the process of setting up virus-free or virus-tested root-
stock sources inevitably involves the selection of a limited number of shoot
tips for heat treatment or meristem culture, and the plants derived from
these selections have been found to differ even if all are of similar virus-
free status. Some of the apparent differences may be ontogenetic and re-
flect differing degrees of juvenility, plants from juvenile sources being easier
to root but spinier in the nursery and not floriferous. Some such differences
may relate to the source material; for example, a rootstock bed in the nurs-
ery may be maintained in a juvenile phase by regular cutting back whereas
a virus-free rootstock mother-tree may be in the adult phase (van Oosten,
b). Such juvenility-related differences may be fairly transient although
van Oosten suggested that the observed effect of different sources of 'M.
'
on the vigour of scion trees worked on to them could be because juvenile
plants root more easily, give larger rootstocks and, in turn, more vigorous
maiden trees. There are, however, some differences between sub-clones that
are large and long-term in nature. Parry (
) demonstrated that the 'M.
a'
clone of 'Malling
' was much more dwarfing than the parent type or the
later 'M.
EMLA', and it is also less productive in the nursery. Wertheim
(
) found trees of 'Red Boskoop', 'Cox's Orange Pippin', 'Jonagored'
and 'Red Elstar' on 'M.
Fl
' to be less vigorous than on other clones
of 'M.
'.
Rootstock effects on scion performance
Control of scion vigour
Theappletreegrowingonitsownrootsasaseedlingorrootedcutting,oranap-
ple scion growing on a genetically similar seedling rootstock, is, in general, too
