Flowering in strawberry is known to be significantly affected by temperature and photoperiod (Kumakura and Siilsiildo, 1995), and the floral initiation of strawberry is regulated by a complex set of environmental and physiological cues (Awang and Atherton, 1995; Opstad et al., 2011; Sønsteby et al., 2013). Furthermore, the appearance and development of inflorescences are significantly influenced by genotype as well as several environmental factors such as temperature, light intensity, and light quality/photoperiod (Nestby and Sønsteby, 2017; Zahedi and Sarikhani, 2017). Researchers have attempted to explain how various lighting environments affect plant physiological responses such as leaf initiation, time to flowering, flowering rate, and fruit quality. Cervantes et al. (2019) evaluated several strawberry genotypes under multiple light exposure treatments and evaluated how genotype and light exposure interactions affected fruit quality. Choi et al. (2016) showed correlations between multiple photosynthesis-related parameters and lighting environment by measuring fruit productivity. Tsuruyama and Shibuya (2018) reported that different photoperiods in controlled environment chambers altered the growth and flowering responses in seed-propagated strawberry seedlings; moreover, flower bud initiation after transplanting was likely accelerated by increasing the photoperiod length. Takeda et al. (2010) evaluated the effect of using photoselective shade nets over strawberry plug plants and concluded that because of the removal of the light signal that initiates flowering, the initiation of flower buds was delayed. Overall, research has shown that increasing both light and photoperiod increases productivity and fruit quality. However, most studies focus on individual strawberry plants of different genotypes and their response to different lighting conditions or different light effects on growth and yield (Cervantes et al., 2019; Choi et al., 2014; Mochizuki et al., 2019; Nestby and Sønsteby, 2017; Young and Ho, 2013). Understandably, the number of buds determines the harvest to a large degree. Therefore, evaluating the variability of flowering characteristics of a whole population will likely produce results that are more applicable in a commercial production setting as compared with genotypic response evaluations.
In Japan, strawberry plants are transplanted once the differentiation of primary inflorescence has occurred into commercial off-season production greenhouses in mid-September, and the fruit is harvested from late November to June (Kumakura and Siilsiildo, 1995; Yoshida et al., 1997, 2012). Owing to environmental conditions and seasonal changes that occur after transplanting, the time to flowering of the second inflorescence increases, which is directly related to the increase in time required for fruit formation. Uniform flower development is also directly related to how uniformly fruits mature, which is important for the logistics and planning in commercial production. Furthermore, to improve harvesting techniques and increase fruit shelf life, Miyashita et al. (2019) suggested that investigating and promoting flowering uniformity would promote uniformity of maturation and allow cluster harvesting in blueberries.
To analyze the effects of different lighting conditions, we applied shading treatments and light-emitting diode (LED) exposure treatments. The aims of this study were 1) to investigate the variability of uniform flower development in different light environments and 2) to evaluate the photosynthetic performance of strawberry and how it is related to maintaining uniformity with a population.
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