PGRs and LEDs in U of G studies

August 27, 2008
Written by Dr. Theo J. Blom, Instructor, University of Guelph
Suggestions from growers often find their way into the  classroom labs

Introduction: This is the sixth year that I have assembled the abstracts of the students in the greenhouse crop production course. This course is a prerequisite for obtaining the undergraduate B.Sc. Agr. degree, and is usually taken in the third year. Besides the (inspiring?) lectures, the students are also fulfilling a lab portion, which usually focuses on a research topic. Thanks to those growers who have contacted me with possible research topics during the year. Many projects deal with studying the effect of an environmental factor on the growth and/or development of a plant/species. It allows the student to get an idea of what research is all about and they get to work with plants in a real setting. The results may not be conclusive, although we often get an indication on where the research is heading. The following are five short summaries from the winter semester of 2008.

Photoperiod control by LED lights using cycling lighting in chrysanthemums
By Christine Tobin and Shannon O’Dwye

Growers often apply supplemental lights to create long days for chrysanthemum crops in order to produce larger plants – by maintaining vegetative growth – and prevent flower induction. Incandescent lights are currently a popular choice among growers. However, a significant cost savings may be possible with the use of light-emitting diodes (LED) lights. This is because they provide an average electrical efficacy of 50 lumen/W compared to traditional incandescent lights that only provide 15 lumen/W.

For this experiment, red LED lights (wave length ~ 630 nm) were used in a cyclic pattern. This consisted of six minutes “on” and 24 minutes “off” each night, from 10 p.m. until 2 a.m. The lamps were in a linear bar (~ 80 cm long) positioned at the short side of one bench and thus created different intensities along the length of the bench. The plants (rooted cuttings in 10-cm pots) were set up in nine different light intensity treatments, ranging from 0-5.5 µmol/m²/s. The results showed that plants remained vegetative above 2.8 µmol/m²/s while plants below 1.7 µmol/m²/s became generative.

This research demonstrated that red LED lights using cyclic lighting were effective in controlling the photoperiodic response of chrysanthemums.

Figure 1. Low LED light intensities from 0 to 1.7 µmol/m²/s resulted in generative chrysanthemums (left), while light intensities from 2.8 to 5.5 µmol/m²/s maintained vegetative plants (right).

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The effect of calcium concentration on leaf tipburn of hydroponically grown lettuce
By Brad deJong and Etienne Papineau

Leaf tipburn is a physiological disorder commonly found in lettuce production.

Two butterhead lettuce cultivars (‘Pybas Red Butter’ and ‘Buttercrunch’) were grown hydroponically in an NFT system using a Hoagland solution. Four concentrations of calcium (0, 1, 2, and 4 mmol/L) were compared in order to evaluate the effect of calcium on the incidence of leaf tipburn. The results (Figure 2) showed that reduced calcium levels resulted in increased leaf tipburn. By reducing calcium concentrations below 2 mmol/L, or 50 per cent of the recommended rate, significant increases in tipburn incidence and substantial reductions in plant leaf area and fresh weight were observed. ‘Buttercrunch’ was more susceptible to leaf tipburn than ‘Pybas Red Butter.’

Figure 2. The effect of Ca++ concentration on the incidence of leaf tipburn of ‘Buttercrunch’ lettuce.

Single and split applications of the plant growth regulator, Sumagic™, at varying concentrations on Lilium longiflorum ‘Nellie White’
By Diana Chapman and Laura Maurice

Sumagic™ (a.i. uniconazole) is a plant growth regulator widely used in the industry to keep Easter lilies within marketable target height. We tested the effectiveness of foliar and drench split applications (double or triple split versus a single application). All applications were applied at the end of January. The total amounts of active ingredient per pot were kept the same. All plants treated with Sumagic, both foliar or drench, showed lower plant height compared to the control. Plants treated with a drench at 1.8 mg of a.i./plant were about one-half the height of the control. Leaf senescence was particularly prominent in the drench treatments. Overall, there were no conclusive results that suggested split applications were more effective than a single application.
Figure 3. The effect of drenching Sumagic at 1.8 mg of uniconazole on Easter lilies. Left to right: control; single application (180 mL @ 10ppm); two applications at 5 ppm; three applications at 3.33 ppm. The split treatments were applied 24 hours apart. Note the effect of excessive dosage on the droopiness of the leaves.
The effect of frequency of irrigating cold water on the height of Easter lilies
By Louise Robertson and Jacob Yantzi

Cold-water applied directly to the Easter lily shoot apex reduces stem elongation. Different cold water irrigation frequencies were evaluated to determine their effect on height. Emerged potted “Nellie White” Easter lilies were irrigated with cold water nutrient solution

(375 ppm N) applied directly onto the shoot apex using three treatment frequencies of 100 ml twice per week, 200 ml once per week, and 400 ml biweekly. The nutrient solution temperatures ranged between 0.5 and 1.9ºC. The control plants were treated with ambient (20ºC) nutrient solution to the shoot apex. The treatments covered a six-week period from Jan. 18th to March 6th. The results showed that as the frequency of cold water application increased, the plant height decreased. Both the 100 ml twice per week and the 200 ml once per week cold water treatments were significantly shorter than the controls. Water temperature did not affect bud abortion or the number of yellow leaves, and there was no significant delay in bloom.

Figure 4. The effects of cold water frequency applied from Jan. 18 until March 3 on Easter lilies. (From left to right) control; 100 ml twice a week; 200 ml once a week; and 400 ml biweekly using 2ºC water. Plants were chosen as an average representation of each treatment on March 3,

The effects of pH and sucrose on the flower longevity, bud abortion and water uptake of Asiatic hybrid lilies
By Chris Duyvelshoff and Carson Tiede

Floral preservatives generally contain a carbohydrate source and one or more bactericides to increase vase life. The effects of sucrose and acidity in vase solutions on cut Asiatic hybrid lilies were evaluated in two cultivars. Two stems, one of each cultivar, were placed in vases with or without a 3 per cent sucrose solution at pH levels of 4, 7 and 10. Water uptake was significantly reduced in the vase solutions containing the 3 per cent sucrose solution regardless of pH. The flower longevity of individual flowers, as well as the ratio of opened to aborted buds, was not affected by sucrose or pH level. Sucrose addition was found to cause rapid yellowing of the leaves within the first five to seven days after placement in the vase solution. Common florist practices use sugarless solutions or defoliate lilies to avoid this problem. ■

Figure 5. Overview of the vase solutions (from left to right): pH 10 + 0% sucrose (S), pH 10 + 3% S, pH 7 + 0% S, pH 7 + 3% S, pH 4 + 0% S and pH 4 + 3% S. Black bars indicate the level of solution remaining in vases after two weeks.

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