‘The main objective of the trial was to verify the impact of the Valoya NS2, AP67 and AP673 LED grow lights on Phalaenopsis cultivation, while simultaneously comparing them with HPS lights,’ says Titta Kotilainen, Research Manager for Valoya. ‘What we found was that plants placed under AP67 and AP673 LED during the flowering stage (phase III) had significantly more flower spikes than NS-2 and HPS, regardless of the light source used during the cultivation stage (phase II). At similar temperature and PAR* light conditions, this clearly seems to be an effect of the light spectrum. Especially Valoya AP67 showed good response in flower production. Compared with HPS, there were on average 23% more flowering spikes and 22% more buds. This is in line with our previous experience with several plant species cultivated under AP67’, she continues.
Chart 1: Number of flowering spikes in plants grown under different light sources.
Chart 2: The percentage of plants with two flower spikes from each light treatment, 16 weeks after flower induction.
Disadvantage of HPSIn professional Phalaenopsis cultivation a day length of 14 hours is usually maintained throughout the year. During the winter months HPS lights are used to augment day length. These lights have the disadvantage of radiating not only visible light, but also infrared radiation, causing the leaves to be warmer. Especially during phase III, when plants need increased light levels but lower temperatures, this means more cooling capacity is required,’ says Gonçalo Neves, Technical Manager for Valoya in the Netherlands.
Energy efficiency and other improvement possibilities in cultivation‘There is evidence that the plant development under LED can be further optimized,’ says Ron Galiart, Senior Researcher at PlantResearch. ‘ Purple colouration in the leaves during the vegetative stage indicate some excess assimilation capacity that is not translated into higher biomass. A slightly higher cultivation temperature during stage II of the cultivation may solve this.’ Moreover, calculations based on the experimental setting suggest that Phalaenopsis can be grown more energy efficiently under LED.
Leaf development‘The number of leaves grown during phase I was significantly higher for plants grown under AP67 when compared to the other light sources,’ adds Galiart. ‘Leaf morphology however - determined by length and width - was not affected. Looking at the phase II plants, no differences in the number of leaves formed during the trial were observed between the different light sources. This demonstrates that the smaller phase I plants respond differently to light spectra than the phase II plants.
From plantlet to flower spike‘Phalaenopsis culture is subdivided into three phases,’ explains Marcel van Twist from Anthura, who was consulted for cultivation related matters during the trial. ‘First in vitro propagated plantlets are placed in so called community trays (phase I). This is followed by a growth phase, whereby the young plants are transferred to transparent 12 cm pots and grown until they reach 4 to 5 fully developed leaves (phase II). Finally, the full grown plants are subjected to lower temperatures in order to induce the formation of flower spikes (phase III). The trial at PlantResearch covered all three phases of Phalaenopsis culture, but because of efficiency, cultivation phase I and II were conducted in parallel.
‘In general cultivation, plants would be pre-selected before entering phase III (flower spike induction), based on plant size. This increases the chance of having two or more flower spikes. In this trial it was found however that over 70% of the AP673 and AP67 grown plants had two flower spikes compared to 50% of the plants grown under other light sources, without any pre selection. This result may reduce the costs for pre-selecting the plants by growers,’ says Van Twist.
Phalaenopsis is the most cultivated flowering pot plant in the Netherlands. In 2013 some 126 million plants were sold through the combined flower auctions of FloraHolland, for a total value of € 475.4 million.
Most cultivated flowering pot plant
The plants in the PlantResearch trial were cultivated according to Dutch greenhouse practice, whereby the vegetative growth phases (I and II) were kept at a minimum of 28°C and maximum 31°C during the day, while the night time minimum temperature was kept at 27.5°C. For flower spike induction, day time minimum temperature was lowered to 20°C, with a maximum of 22°C. During the night time minimum temperature was reduced to 18°C for at least 12 hours per day. Further additional CO2 was dosed in the greenhouse at an average rate of 650 ppm.
* PAR designates the light wavelengths from 400 to 700 nm that plants use for their photosynthesis
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