Dragon Fruit
I
have pieced all the pieces together on Pitaya Flowering and fruit
production using Light Supplementation. Here is my opinion
(semi-scientific from experience and collected works) NOTE: seeds and
cuttings of Pitaya are “Long-Day” sensitive and should root
and grow better after Spring Equinox when going into long days. H
Undatus (and related species) are Long-Day plants, which flower and
fruit between the Spring Equinox and finish, usually before the Fall
equinox. (Autumn). Conjecture 1) --- The Pitaya flowering process
generally kicks in around the year’s longest day, following up on
the continuously increasing day length from the Spring Equinox. By
then, the Pitaya’s Phytochrome protein (Pr.) has absorbed light
from “daylight” at a frequency of (red 660nm) and converted
the Phytochrome (Pr) into (Pfr.). The now active Pfr., has been forced
into the plant’s cell nucleus to create flowering hormone. At
dusk each day this (Pfr) absorbs the setting sun/dusk light (Far-red
light at 730nm) this shocks the (Pfr) back into inactive (Pr) and
moved it out of the cell nucleus. This switches off the flowering
signal. Obviously because the days are long the Pfr remains active in
the nucleus for long enough to create enough flowering hormone to cause
flower buds to appear. Classical flower initiation onset, after the
longest-day, is about 2 weeks, when up to about five flower buds will
appear on a plant. Many will become open flowers after about 2 more
weeks. All the other peripheral plant environmental-factors such as
fertilizers, temperatures, stresses, droughts, or water, are not
significant influences on the flowering onset. They all only promote a
good healthy plant and a good yield.
Light Supplementing Pitaya
plants are slightly smarter than politicians so we can fool them most
of the time. As the Fall Equinox approaches the day lengths start to
shorten and the (Pfr) {which is active} in the cells during light
periods, starts to get changed back into (Pr) {inactive} increasingly
sooner, and hence less and less flowering hormone is processed. In
normal terms, by the Fall Equinox (equal day/night) the flowering
process stops. We can, and the Asians do, enhance this late flowering
process. Provided temperatures do not drop too much and the plant
has lots of stored energy, we can implement a late yield. By using
Incandescent lamps, (incandescent lamps have a better (red @ 660nm)
than most other type’s of lamp. Some specialty
“grow” fluorescent lamps have good red, but they have low
lumen output at any distances from the plants.
Lamps simulate
“Long-days”. The name of the game here is to shock the
(Pr) {inactive} Phytochrome, which regresses during increasing dark
periods, back into active (Pfr ) and to drive them back into the cell
nucleus, to keep making flowering hormone. We can either light the crop
continuously after dark or light the “dark” period for 25%
of each hour, usually starting at about 10pm and continuing until
approx 2.00am. This fools the plant into thinking it is all one long
day. Plants yield better when they sleep a bit at night so they can
rearrange their sugar storage efficiently. However, a continuous light
from 10pm to 2.00am can be used with no real ill-effects. 100 Watt
incandescent bulbs are usually used, spaced about 5 feet apart from
each plant, delivering about 10 lumens {foot candles}. The actual
lumen output is not very critical because all it has to do is shock the
Phytochrome with a few photons. To save power, the lights can be cycled
on and off to give about 25% timed light. There is a technique being
used lately where 400 Watt Metal Halide or Sodium (High Intensity
Discharge) lamps are mounted high enough above the crop to reach plants
40-50 feet away which are either swivelled on a boom or reflected by a
reflector, like a “light house”, causing light to fall on
each plant 3 of 4 times an hour between 10pm-2.00am. The HID’s
are not very high in 660nm red but they make up for it in Lumen output.
Again, provided that each plant feels the equivalent of about 10 lumens
of light at each passing, the Phytochrome will be switched back to
creating flowering hormone. Taiwan is reported to be creating an
additional flowering season, extending from the Fall equinox through to
the next spring equinox. This de-facto means that the plant is in
continuous production. Cooler off-season crops actually have the
capacity to make larger sweeter fruits because the plant can deposit
more sugars in the fruit when their metabolism is not racing at full
speed in the heat. Pitaya fruit can be grown from between 35 – 50
days with no excessive sweetness increase but up to 25% increase in
weight. This may be a good way to get a high yield out of the second
crop even if the plants get tired. Provided the plant nutrition can be
adequately maintained, and the temperature kept within the
plant’s comfort zone, continuous production is possible and
feasible.
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