Agriculture Reference
In-Depth Information
Table
Resistance to
Phytophthora cactorum
as measured by the lesion length on cut shoots placed in
inoculated agar medium
.
Resistance
Mean lesion length
Rootstock
classification
(mm)
a
'J.
'
-
.
a
'M.
'
R
.
ab
'P.
'
-
.
ab
'O.
'
-
.
abc
'A.
'
-
.
abc
'P.
'
-
.
abc
'P.
'
-
.
abc
'M.
'
R
.
bc
'B.'
-
. cd
'M. '
MR
. cd
'M.'
MS
. d
'MM.'
MS
. d
'MM. '
S
. c
a
Mean separation by Duncan's Multiple Range test
(
P
<
.
).
From Utkhede and Quamme (). Reproduced
with permission.
moderatelyresistantand'MM.
'assusceptible.Similarly,'B.
'waslessresis-
tant to
P. cactorum
in tests carried out by Utkhede and Quamme (
) than was
'M.
).
A possible reason for these discrepancies lies in the different pathogenicities
among isolates of
P. cactorum
and different responses of the different rootstocks
to these (Sewell and Wilson,
', although classed as very resistant by Cummins and Aldwinkle (
). Although the resistance to woolly apple
aphid transferred from 'Northern Spy' to the 'Merton' and 'MM.' rootstocks
has been immensely valuable, some biotypes of woolly apple aphid capable of
colonizing 'Northern Spy' and the 'M.I' and 'MM.' stocks have been identified
(Cummins and Aldwinkle,
). A number of 'CG.' and 'G.' series rootstocks
are resistant to fire blight and to
Phytophthora
root rots (Robinson
et al.
,
).
'M.
') is resistant to
Phytophthora
crown and collar rots, mildew,
woolly apple aphid and the specific apple replant disease common in the UK.
Apple rootstocks also influence the incidence of diseases of the scion through
mechanisms distinct from those of rootstock resistance. Sewell and Wilson
(
' ('AR.
.
.
) found that the rootstock effect on scion resistance to
P. cactorum
was in-
versely related to the effect on tree vigour and not related to inherent rootstock
resistance. The degree of scion susceptibility to fire blight is greater the more
dwarfing the rootstock and is influenced by rootstock effects on precocity of
flowering (Cummins and Aldwinkle,
).
