Abstract:
The effect of canopy orientation on fruiting performance of 'Beurre
d'Anjou' pears (Pyrus communis L.) and postharvest urea spray on ovule
longevity and fruit set of 'Doyenne du Comice' pears were studied.
Hedgerows of 'Beurre d'Anjou' pear trees planted in 1969 in two
orientations north-south (N-S) and east-west (E-W) were used to study the effect
on pear fruiting. The trees were spaced 1.3 x 3.7 m, trained to a central leader,
and mechanically pruned to a tree wall 3.7 m high and 1.8 m wide at the base
with a wall angle of 170 from the vertical.
Flower density (FD), flower buds per unit branch cross-sectional area
(BCSA), was lowest on the N wall of the E-W rows in 1990 and on the S wall of
the same rows in 1991. In both years, N-S rows had higher FD. Fruit set (FS),
fruit per flower buds, was highest on the S wall and lowest on the N wall of the
E-W rows, whereas, the E and W walls of the N-S rows were intermediate. Crop
density (CD), fruit per unit BCSA, had a similar pattern as FS with more fruits
on the S wall and less on the N wall of the E-W rows. However, CD was more
evenly distributed between the walls of the N-S hedgerows. Differences in FS
and CD between sides were correlated to different levels of sunlight interception.
For instance, the mid height of the N wall of the E-W rows received less than
20% full sunlight throughout the growing season whereas the S wall received
more than 35% of irradiance especially towards the equinoxes. Increased solar
heating on the S and W walls late in the season led to more sunburned fruits.
Fruits from E-W rows were larger and less firm.
'Doyenne du Comice' is generally considered as a commercial pear
variety with highly palatable fruits. A shortcoming of this variety is, however, that
its trees come into bearing late and then set a small crop. The possibility of
altering ovule longevity and fruit set of this cultivar by nitrogen fertilization was
investigated. Mature trees were given a single foliar application of 5% or 10%
urea immediately after harvest. Ovule senescence was detected by fluorescence
microscopy. Ovule longevity was extended in both treatments in comparison to
control. FS was increased after a foliar application of urea when based on trunk
cross sectional area. There was no effect on FD, CD, fruit fresh weight, and
yield efficiency of 'Comice' trees treated with postharvest urea sprays.
