Comparison of Photomorphogenesis in Roses and Asiatic Lilies

Posted by David Jones on

Cut flower growers rely on greenhouses to provide them blooms around the year, and it is common for them to grow more than one kind of flowers. Roses and lilies are popularly grown for cut flowers as well as potted plants. Is it possible for growers to use common grow lights for these different species? 

Photomorphogenesis

All the three broad phases of plants - germination, vegetative growth and flowering, can be affected by photomorphogenesis, and LED light quality and quantity can be adjusted for an optimal harvest (1). A comparison of photomorphogenesis and its effect on the two flowers is given in Table 1, from which it is possible to find out in which phases common lighting can be used.

Germination and Sprouting 

In case of this phase, we have no specific information for either rose or lilies. So using general recommendations, blue and red can be used as they favor germination, and far-red should be avoided as it hinders breaking of seed dormancy, to germinate seeds of roses and Asiatic lilies (2). 

In case of lilies, however, it is usually bulbs that are used and not seeds in the nurseries. If bulbs are used, we can once again extrapolate from general recommendations, as we found no studies documenting any particular color constellation for bulbs sprouting. Since blue is advised for vegetative growth, this color should help in sprouting. Another reason to include blue is that it will prevent stems from getting too tall and weak in lilies. Adding red lights can make the stems strong (3, 4). So once again a combination of blue and red is good to help bulbs sprout.

Vegetative Growth

A combination of blue, red, far-red and green are recommended to promote vegetative growth for rose seedlings. Green and far-red reach the lower regions of the plant and help the overall growth of plants. Moreover, red produces thick leaves, and far-red makes leaves larger in roses (2, 3, 5). 
In the case of Asiatic lilies too, a combination of many colors gives the best results. White, red, blue, and orange help the plants to grow faster (6). However, the combination of colors that are optimal for vegetative growth differs for the two flowers.
Stem Elongation 
Stem elongation is required in case of cut flower production in roses, and this is an aspect that growers promote. Increasing far-red achieves longer internode growth. Using a high red to far-red ratio makes the stems strong as well as long (5). 
In Asiatic lilies, stems that are very long are not considered optimum as they can be weak and result when the plants receive insufficient light in terms of duration and intensity (7). This is especially true when lilies are forced to bloom and when their vegetative growth happens in winter. So to prevent long stems, adequate durations of light should be provided. It can be a combination of white, red, blue, and orange, or a combination of red with far-red; or just white can be used alone too (6, 8). 
Since stem lengths requirements are different in both cases, so is the color rendering. Here light duration is also an important consideration.
Table 1. Photomorphogenesis in Rose and Asiatic Lilies

 

Rose Asiatic Lilies
 

Germination and Sprouting

Blue and red light are necessary, and far-red should be avoided.

Blue and red light promote strong vegetative growth from bulbs.

Vegetative Growth

A combination of blue, red, far-red and green lights are recommended for overall growth.

A combination of white, red, blue, and orange are beneficial.

Stem Elongation

Green and far-red increase inter-nodal and plant height.

Lack of sufficient light makes lilies tall but weak.

Chlorophyll Formation

Blue and red light are necessary, for chlorophyll formation.

Blue and red light are necessary, for chlorophyll formation.

Photosynthesis

Blue promotes photosynthesis and green hinders it.

Blue promote photosynthesis.

Photoperiodism

Rose is a day-neutral plant.

Asiatic lilies are long-day plants and require around 14 hours of light. White or a combination of red and far-red is good.

Bud Formation

Far-red light increases the number of buds.

Bud formation and development is affected by insufficient duration of light.

Flowering

Red light increases the size of roses.

Flowering requires long duration and the correct intensity of light. Otherwise, flowering is delayed.

Plant Health

UV radiation is used to cure plants.

UV radiation can be used to build resistance to diseases.

 

Chlorophyll Formation and Photosynthesis 
Once again in the absence of specific studies on the influence of light color on chlorophyll accumulation and rate of photosynthesis we rely on the same rule of thumb, i.e., using a combination of blue and red to increase chlorophyll amounts and promote photosynthesis, in both cases (4, 3). 

So a similar combination of red and blue can be recommended at present for both roses and Asiatic lilies. 

Photoperiodism

It is in terms of photoperiodism that rose and Asiatic lilies differ most from each other. The rose is a day-neutral plant, i.e., its flowering is not affected by the number of hours of daylight (9). So there is no need to provide long hours of light, as the duration of light that it receives is not a problem. On the other hand, too many LEDs can lead to more heat, which can lower rose production (10). 

Asiatic lilies, on the other hand, are long day plants and need more hours of light than darkness to flower (7). So it is the duration and intensity of light that also become important for lilies beside color rendering. Without adequate length of daylight, bud abortion and desiccation can occur in lilies. Around 14 hours of light should be provided at the start of bud-formation and flowering in case of Asiatic lilies (6). 

Flowering
In roses, far-red which stimulates bud formation can be useful in increasing the number of flowers (5). In Asiatic lilies, the combination of white, red, blue, and orange can increase the number of flowers per stem; depending on the variety of the flower(6). 

Red light produces larger roses (11, 12). There is no information on the effect of color on the size of Asiatic lilies. It is, however, important to maintain an ideal cycle of dark and light to initiate flower opening in lilies. 

In the case of Asiatic lilies once again the duration and quality of lighting are important, and color rendering needs also differ between the two groups of flowers (7, 6). 

Plant health

Five minutes per week of UV radiation is known to control powdery mildew in roses (13). For Asiatic lilies, we again make a general recommendation of UV radiation to build resistance in plants (14). 

Roses and Asiatic Lilies have Different Light Requirements

The same color rendering can be used in germination or sprouting, to ensure plant health and for proper photosynthesis in roses and Asiatic lilies. It is important to note that these similar recommendations of color rendering are based on general effects that different colors have on plants. Where more research is available, we know roses and Asiatic lilies have different requirements in terms of color quality or rendering, as well as the quantity and duration of light for the vegetative growth and flowering.

 

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