Agriculture Reference
In-Depth Information
Table
.
Effect of rootstock on solute concentration and nutrient content of the xylem sap
above and below the graft union
Below graft union
Above graft union
Solute
N
P
K
Solute
N
P
K
(mg ml
−
)
(mg ml
−
)
Rootstock
ppm
ppm
ppm
ppm
ppm
ppm
'M.'
.
.
'M.'
.
.
a
.
.
a
is more dwarfing than 'M.'.
After Jones (). Reproduced with permission.
.
With apple, the graft unions of dwarfing rootstocks or interstocks with the scions
deplete solutes in the xylem sap and this effect is greater the more dwarfing the rootstock or
interstock.
The depletion of the xylem sap (Table
.
) is found with respect to N,
P, K, Ca and Mg ( Jones,
). The interstock effect appears to be produced
in the upper union region between interstock and scion.
.
Trees on dwarfing rootstocks show restricted canopy development.
Trees on vigor-
ous rootstocks produce more shoots and greater shoot extension late in the
season than those on 'M.
).
The rootstock effects on shoot growth rate are the result of several factors:
(
', even when all are deblossomed (Avery,
) Dwarfing rootstocks induce wider crotch angles to their lateral branches
and a more spreading tree habit (Hatton,
). This is
in keeping with the habits of the rootstocks growing on their own roots and is
accentuated by the precocious and heavy cropping of scions worked on dwarf-
ing rootstocks. Horizontal branches show both decreased vegetative growth
and enhanced flowering and fruiting (Tromp,
,
; Crabbe,
,
,
), these effects
being at least partially independent (Robbie
et al.
,
) Dwarfing root-
stocks check the growth rate of both vertical and horizontal shoots, the effect
being greater on the former (Webster,
). (
) The heavy cropping induced
by dwarfing rootstocks checks shoot growth in the following year. (
). (
) Trees on
dwarfing rootstocks show earlier termination of leaf production and earlier
leaf senescence and spur leaf abscission (Webster,
).
The net effect is that leaf area per tree, especially towards the end of the
season, is less the more dwarfing the rootstock (Webster,
).
.
Trees on dwarfing rootstocks have lower net assimilation rates per unit leaf area
than those on vigorous ones late in the season.
Net assimilation rates for whole
trees, which represent the balance between photosynthetic production and
respiratory losses were found to be higher for 'M.
' than for 'M.
' and for
'Cox'/'M.
' than for 'Cox'/'M.
' late in the season but not in the early part
(Gregory,
). This may reflect earlier leaf senescence on dwarfing rootstocks
