Agriculture Reference
In-Depth Information
zeatin riboside) total content and
concentration in xylem sap from unworked rootstocks or 'Fiesta' apple
scions worked on these
(Back-transformed values, ng shoot
−
and ng ml
−
sap).
Table
.
Cytokinin (zeatin
+
Shoot
Unworked rootstock
'Fiesta' scion
Rootstock
Content
Concentration
Content
Concentration
'M.'
.
.
.
.
'M.'
.
.
.
.
'MM.
'
.
.
.
.
Rootstock effects significant at
p
=
.
.
Data from Kamboj
et al.
(
b). Reproduced with permission.
Warmund
et al.
(
) attributed vascular discontinuities at the union be-
tween 'Jonagold' and 'Mark' rootstock, followed by weak scion growth, to
inadequate growth of the rootstock and/or scion tissues in the autumn. This
problem was found in trees produced in some nurseries but not in others.
Although Soumelidou
et al.
(
a) found the stages in union formation be-
tween 'Bramley' on 'M.
' and 'Bramley' on 'MM.
' to be similar, the xylem
linking the scion bud to the 'M.
' rootstock contained fewer and smaller
vessels than did the xylem in the union of the scion bud to the 'MM.
'
rootstock.
Mosse and Scaramuzzi (
) found anatomical symptoms of incompat-
ibility in all pear/quince unions studied. They were much more severe in
the 'horticulturally-incompatible' unions between quince and 'Williams” but
also showed, to a lesser extent, at the unions of quince with 'horticulturally
compatible' cultivars such as 'Hardy' and 'Fertility'. The symptoms consisted
of necrotic cells in the phloem at the union, proliferation of phloem rays
and, to a lesser extent, breaks in the xylem. The damage appeared to orig-
inate in the older part of the one-year-old phloem and spread to the rays.
It was not shown in the pear-to-pear unions between pear interstocks and
'Williams''. These unions were so good that the line of union could not be
detected.
The graft unions between dwarfing apple rootstocks, especially 'M.
', and
the scions worked on them generally become very swollen with age, attaining
severaltimesthediameteroftherootstockstembelowandthescionstemabove
( Jones,
; Simons,
). This swelling is progressive over time (Kamboj
et al.
,
b) and the associated abnormalities in conducting tissues may have
increasing effects.
