Potato tuber is rich in starch, proteins, and other important nutrients, making potato (Solanum tuberosum L.) one of the most important staple food and vegetable crops (Abelenda et al., 2019). However, potato crops are susceptible to viral and fungal infections, resulting in yield loss and crop quality deterioration (Chen et al., 2018). The production of virus-free microtubers in sterile environments may reduce the risk of viral infection (Park et al., 2009). The morphogenesis of potato plantlets and the subsequent growth of microtubers are influenced by light (Halterman et al., 2016). However, the artificial light environments for the production of seed microtuber in the sterile environments have not been fully explored.
It has been reported that monochromatic red and blue lights regulate the formation and growth of microtuber (Aksenova et al., 1989; Chen et al., 2018; Fixen et al., 2012). However, studies have yielded inconsistent or contradictory results regarding the effects of red light and blue light on microtuber formation and growth, which may be attributed to differences in the variety, intensity, and peak wavelength of lights used, resulting in a puzzling application in microtuber production. The research has reported that white light is conductive to the growth of cattleya hybrid (Cybularz-Urban et al., 2007), lettuce (Hunter and Burritt, 2004), and spinach (Toledo and Ueda, 2003) and beneficial for photosynthesis because more light could penetrate through the canopy to lower leaves compared with red and blue lights (Park et al., 2013). In addition, white light-emitting diode (LED) can also increase the fresh weight of individual microtuber (Chen et al., 2018). However, little attention is paid to the studies of addition white light to monochromatic light on microtuber formation and growth, and further research is required.
The yield of microtubers is directly determined by the quality of potato plantlets, and increased biomass in potato plantlets helps to induce high yield and quality of microtubers (Pelacho and Mingo-Castel, 1991). Furthermore, the carbohydrates produced by potato plantlets are an important material source for the growth of plantlets and microtubers. Tuberization is also known to be regulated by the availability of carbohydrates—in particular, sucrose, the transported form of sugar, required for starch synthesis (Abelenda et al., 2019). In addition, the distribution and transportation of sugar among leaves, stems, and microtubers regulates microtuber formation and growth. However, few studies have investigated this process in detail.
A shorter dormancy period is vital for potato production at sites restricted by short growing seasons (Eremeev et al., 2008), a longer dormancy is used to limit sprout growth during long-term storage of seed tubers for the subsequent season (Mølmann and Johansen, 2019). Therefore, the quantification of microtuber dormancy is necessary for potato production. Tuber dormancy is related to the size and dry matter content of the microtubers, thus determining storage behavior and sprouting potential (Haverkort et al., 1991). The environmental conditions to which the mother plant is exposed often affect seed dormancy (Zhao, 1995). When Arabidopsis is grown under a high ratio of red-to-far-red light (R/FR), seeds are able to germinate in the dark; however, when grown under a lower R/FR, seeds only germinate under light (Zhao, 1995). The preceding studies show that microtuber dormancy is related to the light environment of mother plant. However, how light spectra influence on microtuber dormancy period after harvesting has not been reported. The sugar content at harvest is one of the important parameters determining the maturity and sprouting vigor of seed potato (Rees and Morrell, 1990) and has a strong effect on crop performance (Donnelly et al., 2003). Whether light spectra influence on sugar content of microtuber and then change the dormancy period is not yet well known.
The preceding issues led us to hypothesize that the addition of white light to monochromatic red and blue lights could alter the formation, growth, and dormancy of microtubers, so we grew potato plantlets under four light spectra provided by LEDs to evaluate the formation, growth, and dormancy of potato microtubers. To assess the effects of the lights, the number, weight, and dormancy period of microtubers were observed. Biomass accumulation and distribution and carbohydrate levels of the potato plantlets and microtubers throughout microtuber production were also measured to assess the regulatory mechanism for microtuber formation, growth, and dormancy induced by different light spectra.
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