Agriculture Reference
In-Depth Information
With resumption of bud growth there is a change in membrane composition
allowing increased permeability of solutes and water to the cytoplasm. Wang
and Faust (
) found that the seasonal changes in membrane lipids in apple
buds from dormancy in winter to budbreak, and bud growth in spring, were
similar to the general pattern of lipid metabolism induced by TDZ. Apple buds
exposed to low winter temperatures responded with an increase in the degree
of unsaturation of the fatty acids of their membrane lipids, changes in polar
head group composition, increases in membrane phospholipid content and
changes in sterol level and composition. The ratio of sterols to phospholipids
decreased during budbreak and bud growth in spring.
Controlling seasonal budbreak
The major problem is that of poor budbreak in climates with mild winters and
little winter chilling. A second problem is that of early budbreak and risk of
damage from spring frosts in temperate-zone fruit-growing areas.
In general the date of budbreak reflects both the chilling and the heat require-
ments of the cultivar in a specific environment (Spiegel-Roy and Alston,
;
Petropoulou
a). There is considerable vari-
ation between existing cultivars in these respects. At the National Fruit Trials
in Kent, England the range of budbreak (flowering) dates of apple cultivars was
from
; Hauagge and Cummins,
April for 'Nico' to
June for 'Spatbluhender Taffetapfel' (Morgan
and Richards,
). In Zimbabwe the date of first budbreak of 'Anna' was
about
months earlier than that of 'Starking' (Bepete and Jackson,
) and
in Brazil Bernardi (
) found 'Anna' to be more than
months earlier than
'Red Delicious'.
The most widely used apple cultivars in warm-winter areas are of two types.
The first are those which show only shallow depth of dormancy as well as
limited requirements for chilling. 'Anna' and 'Dorsett Golden' are the most
widely grown and adapted to the mildest winters (Miller and Baker,
).
'Ein Shemer', 'Elah', 'Maayan' and 'Michal' have also performed well in
tropical and subtropical areas with inadequate winter chilling for mainstream
cultivars.
The second type are exemplified by 'Rome Beauty' which, although clas-
sified as having a high chilling requirement, can be prevented from entering
deep dormancy by leaf stripping following branch bending ( Janick,
). Its
tip-bearing habit may be important in this respect.
In intermediate areas, still too warm in winter for traditional cultivars,
'Mutsu' and 'Braeburn' have both shown excellent cropping and leafing out
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