Agriculture Reference
In-Depth Information
main selection criterion for a particular group of apple cultivars for use in
home gardens or even on patios. These are the Columnar apples which have a
spur-type habit inherited from the mutant 'Wijcik McIntosh'. These trees bear
fruits on spurs along the main central stem, have very few branches and need
very little pruning; examples are 'Waltz', 'Polka', 'Bolero' and 'Flamenco'.
Independently of vigour, apple cultivars can be classified into four main
morphological types (Lespinasse and Delort,
).
Spur-types, in which the scaffold branches are conical and tend to develop
sub-branches on their lower surface (basitony). The central leader, the
trunk, is not particularly dominant in all cultivars. Most fruits are on short
spurs on branches two years old or older.
'Reine des Reinettes' types, with main branches making wide angles to
the trunk, a relatively dominant centre leader but strong growth of lower
branches.
'GoldenDelicious'types,withastronglydominantleaderwithwide-angled
fruiting branches coming directly off this and numerous short shoots.
These trees are well suited to vertical-axis and spindlebush types of tree
management.
'Rome Beauty' types, which rarely develop lateral shoots in their lower
regions but develop overarching and drooping branches in the upper part
of the tree, i.e. with an acrotonic tendency. This results in the fruiting zone
moving towards the upper and outer zones of the tree.
These types are shown in Figure
.
(p.
).
Disease resistance of apple cultivars
Although there are cases where disease susceptibility has prevented a cultivar
being grown in a particular environment, e.g. 'McIntosh' is too susceptible to
apple canker to succeed in England, none of the cultivars listed in Table
is important primarily because of its disease resistance. The 'Delicious' group
have a degree of resistance to powdery mildew and fire blight and are very
resistant to cedar apple rust, but even they depend on fungicides for the pro-
duction of blemish-free fruits.
There is, however, increasing interest in foodstuffs produced without the use
of chemicals and a number of apple cultivars have been bred for resistance to
the major diseases. Apple scab, caused by the fungus
Venturia inaequalis
,isthe
mostseriousdiseaseofapplesworld-wide.Bothpolygenicandmonogenicresis-
tance are available and some new cultivars have shown virtual field immunity,
to the extent that orchards of them have produced scab-free fruits for many
years without being sprayed. Most resistant cultivars have the
Vf
resistance
gene from
Malus
.
×
floribunda
, perhaps the most important at present being
