From the Sub-Tropical Fruit Club of Qld Inc.
by Graham Reindeers

Seasons in Australia are opposite to those in the US.  Summer is Dec. Jan. Feb. Autumn is Mar. Apr. May. Winter is June July Aug. Spring is Sept. Oct. Nov.

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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Reindeers, Graham. "Dragon Fruit." Sub-tropical Fruit Club of Qld Inc. newsletter, Dec. 2010. Web. 21 June 2017.

Published 12 Apr. 2017 LR
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