Agriculture Reference
In-Depth Information
densities can reach or exceed 75,000 plants/ha. In Hawaii, the maximum day-
length range between the shortest and longest days is about 2.5 h, but solar
irradiance in December is about 50% of that occurring during midsummer.
Sun injury of leaves is relatively uncommon in most regions where pineapple
is grown, as air temperatures do not exceed about 35°C. When greater than
35°C, the leaf 's surface temperature on a horizontally displayed leaf is likely
to exceed 50°C. Because of close plant spacing on commercial plantations,
pineapple leaves are erect, as they are supported in an upright position by the
leaves of closely spaced adjacent plants. Erect leaves help to distribute high
midday irradiance uniformly over the leaf surface and help to reduce the heat
load borne by the leaf. Due to relatively erect leaf orientation, about 95% of
light interception occurs in a pineapple canopy at a leaf area index (LAI) of
about 5.0.
Fruit weight is signifi cantly correlated with mean irradiance from planting
to harvest (Fig. 12.4). The lower fruit weight associated with lower irradiance
is due to a lower plant weight at forcing. Fruit acidity in the month before
harvest declines with solar radiation levels and there is no signifi cant ef ect on
total soluble solids. Cloudy days reduce pineapple growth and result in smaller
plants and smaller fruit, with higher acid and lower sugar contents. A rule of
thumb is that for each 20% decrease in solar radiation, the yield decreases
~10%. Mutual shading at higher planting densities leads to a linear decrease
in individual fruit weight and a curvilinear increase in total yields as density
increases.
Intense sunlight, particularly during fruit maturation, can cause sun-
scalding of fruit, with the 'Queen' group being more susceptible than 'Smooth
Cayenne'. The damaging ef ect can be prevented by shading the fruit or
spraying a refl ective coating, for example lime and a spreader-sticker, as is
done in Queensland, Australia. Fruit covered with newspapers or grass, or the
gathering and tying of the longest leaves over the fruit is observed in Okinawa
and Taiwan and is also a common practice in Mexico and Brazil.
Photoperiod
The normal season for fl owering of 'Smooth Cayenne' is during the winter,
in response to cool temperatures and shortened photoperiod. However,
the plant will fl ower naturally at any time of the year, depending upon the
planting material and time of planting (Bartholomew
et al.
, 2003). Because
of this response, Gowing (1961) classifi ed 'Smooth Cayenne' as a quantitative
but not an obligate short-day plant. Under controlled conditions, 'Smooth
Cayenne' plants grown under 8-h days all fl owered; 69% fl owered under
10-h days, 53% under 12-h and 30% under 16-h days (Friend and Lydon,
1979). Interruption of the dark period by illumination suppresses fl owering.
Before the advent of artifi cial fl oral initiation, plants that were not induced
to fl ower during the winter months generally fl owered in the late summer
and early autumn, producing winter and spring fruit. Some minimum
