Agriculture Reference
In-Depth Information
9
8
7
6
5
4
0
2
4
6
8
10
12
Subculture number
Figure 3.4
Rejuvenation with increasing subculture of initially
poor-rooting somaclones of 'Greensleeves' apple. From Donovan
et al.
(1994). Reproduced with permission.
juvenile-like characteristics when grown in the field (Jones and Hadlow,
),
and conventional cuttings taken from micropropagated plants (plants pro-
duced
in vitro
) showed improved rooting for both apple and pear (Table
.
;
James
et al.
,
).
In vitro
cul-
ture may lead to excessive development of burr-knots and suckers (both char-
acteristic of juvenile, ready-rooting material) when the rootstocks are planted
directly from micropropagation into the field. This problem is reduced if the
rejuvenated plants are used as source material for conventional propagation
(Jones and Webster,
; Jones and Webster,
; Webster and Jones
).
Stem cuttings form shoots at the distal end, i.e. nearest the shoot tip, and
roots at the proximal end, i.e. nearest the original root system. This polar-
ity is correlated with auxin movement (Robinson and Schwabe,
).
Rooting potential is higher in the proximal parts of annual shoots of ap-
ple rootstocks, especially in the basal region (Howard,
; Howard
et al.
,
).
Theproductionandemergenceofshoot-bornerootsisnegativelyrelatedtothe
continuity of the sclerenchymatous sheath arising from the primary phloem.
This relationship holds with respect to the rooting of dormant winter cut-
tings (hardwood cuttings) of a range of apple rootstocks and apple and pear
