Effect of Different Light Sources on Morphology and Growth of Potato Plantlets under in-vitro Conditions and their Effect on Minituber Production in Greenhouse

Conventional seed programmes take more than 10 years and diseases during each round of field multiplication become increasingly common and especially those transmitted through seed tubers. In contrast, the production of large volume of propagation material in protected environments requires only a few additional years of traditional seed multiplication in the field to produce the desired seed with an improved health status. This is useful especially in countries where there are no vector-free production areas for producing high quality potato seed tubers. In the last few decades, alternative seed production programmers have been developed in which the first multiplication steps are speeded up using in vitro plantlets, microtubers or minitubers. In the area of controlled environment agriculture (CEA), one of the most commonly discussed topics is lighting. The lighting system is generally the most expensive component of a controlled environment agriculture facility in terms of upfront costs as well as ongoing expenses (electricity use as well as replacement lamps). Naturally, advances in lighting technology are of great interest to the controlled environment agriculture community for these very reasons. Light emitting diodes (LEDs) are the most recent lighting technology to enter the controlled environment agriculture arena and have great potential to improve performance and reduce the overall cost of controlled environment lighting. Growth and morphogenetic effects of light (quality, intensity, and duration) and phytohormones are well documented, but their modes of action and mutual interactions are far from clear. One of the important questions is whether at least some of the morphogenetic effects of light are mediated by changes in phytohormone levels. This experiment was conducted in order to study the effect of different light sources on morphology and growth of potato plantlets under in-vitro conditions and their effect on minituber production in greenhouse to decrease energy consumption and production costs.
A factorial experiment was conducted based on completely randomized design with six replications under in-vitro conditions and four replications in greenhouse. Factors were consisted of cultivars (cv. Agria and Savalan) and light sources (LEDs emitting red, blue, white, combination of red and blue and also tubular fluorescent lamps as control). The experiment was carried out at the tissue culture laboratory of Yeka Seed Technology of Iran. Disease-free potato in vitro plantlets of Agria and Savalan cultivars were derived from the potato germplasm bank of Agricultural Biotechnology Research Institute of Iran. The plantlets were propagated using single-node cutting. Eight explants were cultured in sterilized culture vessels containing 30 ml of MS and pH was set to 5.8 before adding agar and autoclaving. Culture vessel were closed with polycarbonate caps and sealed with household plastic foil and were placed in a growth chamber at 24 °C and 16 h photoperiod for 4 weeks.
Results indicated that red spectrum caused an increase in plantlet height and Agria had a higher plantlet height under in-vitro conditions. Root length was higher in red-blue combination and no difference was observed between cultivars under in-vitro condition. The highest and lowest leaf area was obtained in white and red spectrum, respectively. Also, Savalan showed a higher leaf area in comparison with Agria. The lowest node number in plantlets was observed in red spectrum and the highest in white. The highest and lowest internode length was related to red and blue spectrum, respectively. Fluorescent light was resulted in the lowest plantlet fresh weight and no significant difference was observed among other treatments according to this parameter. Stem diameter and number of branches was not affected by different lights. Results of greenhouse study indicated that light conditions before transplanting of plantlets did not affected minituber number, while minituber weight was significantly affected by this factor and the lowest mean of this parameter was obtained in red spectrum compared to the other treatments.
Generally, results showed that less leaf area plantlet in vitro was also less leaf area in greenhouse (red light emitting diode). Leaf area is an important criteria for photosynthetic and biomass production. Therefore, in this experiment fresh and dry matter production was affected by this characteristics and red light showed the lowest dry matter production. LEDs could be considered as suitable light sources producing plantlets comparable with those grown under fluorescent light under in-vitro conditions along with saving energy and ultimately lower production cost.