Agriculture Reference
In-Depth Information
rootstock stem girdled and the tree dies. A rather different manifestation of its
effects is shown by 'Conference' on 'Quince A' or on 'Quince C'. Young trees
of these combinations show premature leaf red colour followed by early leaf
fall. In the following spring the leaves remain small and pale, there being little
or no shoot growth and no fruit production. A necrotic line is frequently visible
in the bark at the stock/scion union. The disease is sometimes fatal but more
commonly just reduces yield in the early orchard years. The quince rootstocks
are rarely infected by the causal phytoplasma, such infection as there is being
mainly in suckers. Quince should be regarded as being partially resistant or
hypersensitive, rather than tolerant (D.L. Davies, personal communication).
'Conference' is readily infected by the phytoplasma, but, when grown on its
ownroots,isvigorousand,althoughinfected,showsnoevidenceofpeardecline
(Davies
et al
.,
). Interestingly, although the cv. 'Comice' is readily infected
it does not show symptoms when worked on quince, but a 'Comice' interstock
between quince and 'Conference' does not prevent the latter suffering from
pear decline.
Double working
A double-worked plant has three parts, the rootstock, the interstock and the
scion; and two unions, one between the rootstock and interstock and one
between the interstock and the scion. Double working is used.
In cases where the rootstock and the scion are mutually incompatible but
each will form a good union with the interstock. A typical example is
the propagation of 'Bartlett' pear on Quince rootstock by using a 'Beurre
Hardy' or 'Old Home' interstock.
Where a rootstock with desirable properties, e.g. dwarfing, is in itself diffi-
cult to root but can give similarly desirable effects if used as an interstock.
This is typified by the use of cold-tolerant, dwarfing, interstocks of the
'B.
' and 'P-series' rootstock clones inserted between a vigorous, cold-
tolerant seedling rootstock and the scion cultivar in climates with severe
winters.
Methods of double working
There are a number of different methods (Hartmann
et al.
,
). In England
it is done as a combined operation using dormant scionwood of both the
interstock material and the upper scion. The wood of the interstock cultivar
is cut into
mm lengths in March and immediately grafted with three-bud
lengths of the upper scion cultivar and the grafts sealed and stored upright in
cool moist conditions. The interstock, with its scion attached, is then grafted
