Agriculture Reference
In-Depth Information
concentration in the xylem sap of apple. This can be expected to have positive
effects on flowering.
Williams (
) found that under conditions of sub-optimal N supply, appli-
cation of nitrogenous fertilizer in summer after the formation of terminal buds
led to increased flowering in the following year. When fertilizer was applied
at the same time to a cultivar that had not ceased extension growth this was
further stimulated and there was no effect on flowering. Nitrogen application
after terminal bud formation also led to the development of flowers with much
enhanced embryo sac longevity.
Water stress effects on flowering
Excessive rainfall or irrigation which maintains extension growth late into
summer will often reduce flower bud formation, but this is inhibited under
moderate drought and nearly completely prevented under severe stress (Salter
and Goode,
).
Exposure to low (
-
%) as contrasted with high (
-
%) relative hu-
midity for
weeks from full bloom increased the proportion of apple buds
becoming floral from
), as well as greatly reduc-
ing shoot growth. With 'Bartlett' pear (
P. communis
), irrigating to replace
%to
% (Tromp,
%,
% and
% of calculated evaporation was followed by, respectively,
.
,
flower clusters per cm
of branch cross-section in the following
spring (Mitchell
et al.
,
.
and
.
). Again, this followed effects in the opposite direc-
tion on shoot growth. However, Caspari
et al.
(
) found that low irrigation
rates (regulated deficit irrigation) early in the season had very adverse effects
on flower production by Asian pear (
P. serotina
). Goode and Ingram (
),
in a long-term apple irrigation experiment, found that the vigorous growth
induced by irrigation did not affect fruiting adversely and Wample (
) con-
cluded that apple trees which have not been stressed enough to stop growth
consistently produce more flowers.
Technologies that promote flowering, e.g. dwarfing rootstocks, appropriate
pruning and tying down of branches, may in many cases overcome the po-
tentially negative effects of vigour-enhancing treatments. The effects of water
and nutrient supply on flower initiation and development may therefore vary
with circumstances.
Plant virus effects on flowering
Virus-free apple rootstocks generally induce more vigorous growth in scions
grafted on them than does the virus-infected 'parent' material (Parry,
).
Initially trees on these virus-free rootstocks were less floriferous in relation to
their size but adoption of minimal pruning and branch bending in the first
years after planting overcame this problem (Van Oosten,
).
