5 DISCUSSION
5.4 Effect of covering material and light quality on chlorophyll content
The chlorophyll content was found to be higher in plants grown under solatrol compared to shade in all treatments 'Tidal Wave and 'Mambo Formula Mixture' cultivars of petunia. The highest numbers were found under solatrol with supplementary red light by red LED. Far red light seems to decrease the chlorophyll content because solatrol led to higher xhlorophyll content. High R/Fr ratio is also inductive for cholorophyll content as solatrol with supplementay red light led to highest cholophyll content. Similarly, leaves treated with far red light led to lower chlorophyll content in Birch (Caesar 1989), Acer species and other deciduous trees (Hanba et al., 2002; Oguchi et al., 2005).
Red LED treatment induced higher chlorophyll content compared to the blue LED treatment in both the experimented cultivars. However, the difference was only prominent under solatrol.
Chlorophyll content in lettuce leaves was also found to decrease with the treatment of blue light (Brazaityte et al., 2006). In contrast, (Poudel et al., 2008) reported that blue LED treatments led to the highest and red LED treatments led to lowest chlorophyll content in grapes. Blue LEDs led to highest chlorophyll content also in upland cotton plantlets (Li et al., 2010). Whereas Shin et al., (2008) reported that chlorophyll content was found to be highest in the plants grown under mixed blue plus red LED, followed by blue LED and florescent treatment and the red LED treatment showed remarkable reduction in chlorophyll content.
54
Compared to blue light, red light was found to be much efficient to increase chlorophyll content in both the experimented cultivars.libird LED can show its effect in higher chlorophyll content but remarkable difference was found only under the solatrol. Thus, presence of red light may be important to increase chlorophyll content in the absence of far-red light. Presence of far-red light minimizes the effect of LEDs in increasing or decreasing chlorophyll. Red light led to phytochrome stimulation, and then signals from phytochrome because of this stimulation may increase the expression of gene to increase chlorophyll content. So phytochrome stimulation in absence of far-red light seems to be important for higher chlorophyll content.
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6 CONCLUSIONS AND RECOMMENDATION
The response to light quality is dependent on cultivar, and ‘Mambo Formula Mixture’ is found less sensitive to light quality than that of cultivar ‘Tidal Wave’.
The covering material solatrol, which does not transmit far-red light, can reduce stem extension but the effect was more prominent under high irradiance (summer experiment) than low irradiance (early spring experiment). The main reason is that Solatrol reduces the total light transmittance with 30% which again enhances stem extension.
Red LED is very effective in reducing stem extension in petunia and can be an alternative in controlling plant height but combined with solatrol it can reduce the number of flowers and flower buds prominently.
Additional blue light will not reduce stem extension of petunia. Rather higher plants were found when blue LED was added under both covering materials.
Earlier flowering and more flowers were found with additional blue light quality.
The light quality treatment did not affect the number of internodes but mainly the length of the internodes.
Also Chlorophyll content of both the cultivars of petunia was higher under solatrol compared to shade.
In summary, petunia is very sensitive to light quality and it can be used as a strong tool to control morphology and flowering. Red light is effective in reducing the stem extension growth (plant height) but blue light, as well as far red light, is the most effective in promoting flowering.
From the study we can recommend the following observation to the growers
The red LED light can be used in the early spring in order to reduce the height of the petunia plants.
The solatrol can be of importance during summer when the irradiance is high and will then reduce the height of petunia.
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