Development of photoselective covers

Growth Chambers(image: YBM-1 (left) and YBM-10 (right) experimental chambers. As the dye concentration increased light transmission decreased. Irradiance indside each chamber was adjusted to be the same with shade cloth or cheesecloth. Chambers are approximately 1m x 1m x 1m.) Mitsui Chemicals, Inc. identified two pigments that absorb far-red light from the natural spectrum and that are stable in polyethylene films or rigid plastic panels. Initial trials focused on identifying a suitable dye and dye concentration that effectively filters out far-red light from sunlight and reduces plant height while minimizing the reduction in light transmission. Mitsui Chemicals, Inc produced rigid plastic panels containing five dye concentrations from each dye. Plants figures(Figure 2. Plant response inside YMB-1 (left column) or YMB-10 (right column) chambers with varying dye concentrations. Within a picture, from left to right, are plants grown in control, #85, #75, #65, and #55 chamber. Within a column, pepper, watermelon, chrysanthemum, tomato, and petunia are shown from top to bottom.)These were identified as control, YBM-1/YBM-10 #85, YBM-1/YBM-10 #75, YMB-1/YBM-10 #65, and YBM-1/YBM-10 #55. The number followed by the YBM indicates the code of the dye. As the dye concentration in the panels increased, the absorption of far-red light increased but the light transmission decreased. The number followed by YBM-1 or YBM-10 indicates the percentage light transmission through each panel. Growth chambers (1 m x 0.8 m x 0.8 m) were built with each of these materials and growth of bell pepper, tomato, petunia, and watermelon seedlings and chrysanthemums cuttings were evaluated inside each of the chambers. All chambers were kept inside a greenhouse and the amount of light inside each chamber was adjusted with neutral density filters (cheesecloth or shade cloth) to be the same among all chambers.

Both types of far-red light absorbing photoselective filters reduced height of all species tested in preliminary trails but the magnitude of height reduction varied with the species. (Table 2 and Figure 2). In general, watermelon seedlings showed the greatest height reduction followed by bell peppers, tomato, and chrysanthemum. Number of leaves was not affected, indicating that height reductions were caused by shorter internodes. The height reduction increased as the dye concentration in the panels increased but total shoot dry weight was reduced because of the severe light reduction as the dye concentration increased. Therefore, a dye concentration that gives a light transmission of 75% was selected for photoselective film production and further experimentation.

Table 2. Effect of dye concentrations in YBM-1 and YBM-10 photoselective chambers on height of chrysanthemum, watermelon, bell pepper, and tomato plants. The number followed by the film indicates the percent light transmission through the panels. Percentage height reductions compared to control plants are given in parentheses.

    Plant height (cm)  
Material Chrysanthemum Watermelon Bell pepper Tomato
Control 29.7 28.4 22.1 -
YBM-1 #85 26.6 (-10) 21.7 (-24) 17.2 (-22) -
YBM-1 #75 23.7 (-20) 14.6 (-49) 13.9 (?37) -
YBM-1 #65 20.9 (-30) 14.5 (-49) 13.9 (-37) -
YBM-1 #55 21.8 (-27) 14.9 (-48) 12.0 (-46) -
         
Control 30.2 52.3 14.5 35.0
YBM-10 #85 31.0 (+3) 38.9 (-26) 11.2 (-23) 32.5 (-7)
YBM-10 #75 25.9 (-14) 38.1 (-27) 10.0 (-31) 23.2 (-34)
YBM-10 #65 26.2 (-13) 35.0 (-33) 9.9 (-31) 23.4 (-33)
YBM-10 #55 27.0 (-11) 33.2 (-37) 9.6 (-34) 23.7 (-32)

Light Spec

Vegetable Transplant(image: Response bell pepper (top), tomato (center), and cucumber (bottom) seedlings to photoselective films.) Based on initial findings, photoselective greenhouse films with red and far-red light absorbing films (SXE-4 and YXE-10 films, respectively) were produced with a dye concentration that results in a 75% light transmission ( light spectrum  (image) of two types of films). Growth of several vegetable transplants and ornamental bedding plants was evaluated inside growth chambers covered with these films. The results are summarized in Table 3. Plants produced under the far-red light absorbing film were, in general, shorter (except snapdragon and miniature roses) than the control plants while plants produced under the red light absorbing film had similar or increased height compared to the control plants. The magnitude of height reduction varied with the species and cultivar.

We also evaluated flowering of selected ornamental crops inside the chambers under natural short day conditions. Flowering of miniature rose plants was not affected (Table 3). Flowering of cosmos, zinnia, and chrysanthemum (short day plants) was slightly delayed (by 1-2 days) under the far-red light absorbing film. Photoselective films had the greatest influence on flowering of snapdragon and petunia (long-day plants). Flowering of these species was delayed by 7-13 days under the far-red light absorbing films. Red light absorbing film did not significantly affect flowering of these species tested.

Table 3. Influence of red and far-red light absorbing plastic films (SXE-4 and YXE-10, respectively) on plant height and flower development (days to anthesis, DA) under natural short days of selected crops. Control is a clear polyethylene film.

  Control film SXE-4 film YXE-10 film
Crop Height
(cm)
DA
(days)
Height
(cm)
DA
(days)
Height
(cm)
DA
(days)
Vegetable crops            
Cucumber ‘Sweet Success’ 17.3 b - 19.8 a - 8.6 c -
Tomato‘Mountain Pride’ 15.0 a - 15.8 a - 11.2 b -
Bell pepper ‘Capistrano’ 11.1 a - 11.4 a - 8.4 b -
Ornamental crops            
Snapdragon            
'Ribbon White’ 48.3 b 63 b 53.8 a 61 b 48.9 b 70 a
‘Tahiti Red’ 25.5 a 51 b 24.7 ab 50 b 23.0 b 59 a
Florida pink 23.6 b 26 a 27.2 a 27 a 22.5 b 25 a
Florida blue 31.2 a 30 a 30.4 a 28 a 27.9 b 31 a
Florida sky blue 26.7 ab 30 a 28.1 a 30 a 23.4 b 32 a
Petunia            
‘Supercascade Burgandy’ - 53 b - 54 b - 66 a
Zinnia            
‘Pumila Mix’ 24.5 b 33 ab 28.4 a 32 b 18.8 c 35 a
‘Cherry Ruffles’ 38.0 a 35 c 40.9 a 36 b 30.4 b 37 a
Cosmos            
‘Sonata White’ 37.3 a 26 a 38.1 a 27 a 33.5 b 27 a
Miniature rose            
‘Cherry Cupido’ 28.8 a 46 a 29.2 a 46 a 27.2 a 46 a
Chrysanthemum            
‘Bright Golden Anne’ 32.6 b 64 a 34.6 a 65 a 28.4 c 65 a
‘Iridon’ 22.6 b 59 a 25.8 a 60 a 19.8 c 62 a
‘Yellow Snowden’ 50.8 a 55 a 50.4 a 57 a 40.7 b 56 a
Pachystachys lutea 30.1 b 38 a 32.8 a 38 a 27.0 c 38 a
Strobilanthes dyerianus 34.2 ab - 38.9 a - 30.2 b  

Film Chambers

Response of Petunia and Snapdragon (long day plants) to photoselective films. 

Snapdragon Petunia

Response of Zinnia and Cosmos to photoselective films.

Cosmos Zinnia

Response to 'Iridon' (top), 'Bright Golden Anne' (center), and 'Yellow Snowdon' (bottom) chrysanthemums to photoselective films. 

Chrysanthemums

Response to Strobilanths (top) and Pachystachys (bottom) to photoselective films.   

Pachystachys

 

Photoselective greenhouse films with red and far-red light absorbing films (SXE-4 and YXE-10 films, respectively) produced with a dye concentration that results in a 75% light transmission.