Agriculture Reference
In-Depth Information
Table
.
Pollen production by different cultivars
+
Flowers
Pollen (g)
Percentage
Flowers,
Flowers
per mm per
germination per mm
per m
Cultivar
branch
flowers
in vitro
branch
canopy
'Egremont Russet'
.
.
'Golden Delicious'
.
.
'Golden Hornet'
a
.
.
'Hillieri'
a
.
.
.
'WinterGold'
a
.
.
a
Ornamental
Malus
.
Representative data taken from Church and Williams (a).
Williams,
b). Cultivars with a long flowering season, e.g. those that flower
profusely both on one-year-old long shoots and on spurs, may be especially
useful as pollenizers. This trait can be accentuated by the type of pruning.
The quantity of pollen produced by a cultivar depends on its flower pro-
duction and the yield of pollen per flower. Church and Williams (
a)
found that some ornamental
Malus
cultivars produced twice as much, or
more than twice as much, viable pollen per metre of branch as cultivars in
general use as pollenizers for 'Cox', while the dessert cultivars also differed
greatly among themselves (Table
). Triploid cultivars may produce large
amounts of pollen but much of this may be defective as a result of chromosomal
imbalance.
Low winter temperatures may reduce both the number of pollen grains
produced and their viability. High temperatures in spring often result in sterile
pollen but the severity of this problem varies with cultivar (Faust,
.
). Anther
dehiscence can occur as low as
◦
C (Percival,
).
Pollen transfer
Apples and pears are insect-pollinated, predominantly by hive bees (
Apis mel-
lifera
L.), bumble bees (
Bombus terrestris
L.), other wild bees and hover flies
(
Syrphidae
) (Smith,
). The efficiency of pollen transfer by insects
depends on their abundance, the relative attractiveness of the apple and pear
flowers to them, their mode of operation and climatic conditions.
Hive (honey) bees are usually the most important, especially on pear (Eijnde,
;Free,
), although they are more adversely affected by low temperatures than
bumble bees or wild bees. In general there is little insect activity below
◦
C
◦
F). Flower visiting by insects, except bumble bees, usually ceases during
heavy rains or showers. Windspeeds above
(
-
m.p.h. inhibit bee flight.
