Air temperature and light conditions are important factors not only to produce high-quality seedlings but also to promote energy efficiency in a plant factory with artificial lighting. In this study, we conducted two experiments in order to investigate the favorable conditions of air temperature, light intensity and photoperiod for the production of cucumber scions and rootstocks in a plant factory with artificial lighting. Cucumber scions and rootstocks were cultivated in two combined treatments: the combination of three different levels of difference between the day and night temperature (DIF), 25/20, 26/18 and 27/16 °C and five different light intensity conditions of photosynthetic photon flux, 50, 100, 150, 200 and 250 μmol·m⁻²·s⁻¹ was set for the first experiment, and the combination of three different photoperiod conditions, 12, 16 and 20 h·d⁻¹ and five different light intensity conditions, 50, 100, 150, 200 and 250 μmol·m⁻²·s⁻¹ was set for the second experiment. In the air temperature and light intensity treatments, the hypocotyl elongation of cucumber scions and rootstocks was affected more largely by light intensity than DIF. The highest DIF treatment (27/16 °C) affected negatively on the accumulation of dry mass. On the contrary, the smallest DIF treatment (25/20 °C) was favorable for seedling growth due to lesser stress by rapid change of air temperature between photo- and dark-period. In the photoperiod and light intensity treatments, an increased DLI (daily light integral) promoted the growth of scions and rootstocks. Under the same DLI condition, the growth of scions and rootstocks increased with increasing photoperiod and decreasing light intensity. In both of experiments, while the dry weight increased with increasing the light intensity, the light use efficiencies were reduced by increasing the light intensity. Considering the growth and quality of seedlings and energy efficiency, the optimal environment conditions were represented by 25/20 °C of air temperature, 150 μmol·m⁻²·s⁻¹ of light intensity and 16 h·d⁻¹ of photoperiod.

The objective of this study was to develop a growth model for grafted hot pepper seedlings as affected by air temperature and light intensity. After grafted union formation, the hot pepper seedlings were cultivated in various environmental factors in terms of four levels, mean daily air temperature (17, 22, 27, and 32 °C) and 3 levels of light intensity (150, 350, and 550 μmol·m⁻²·s⁻¹). The growth traits were measured 0, 7, 14, 21, and 28 days after grafted union formation (DAGU). The plant height was improved, and development of leaves enhanced by higher air temperature. The number of leaves was greatest under the combination of the high temperature and high light intensity, resulting in 39.0/plant at 28 DAGU. The leaf area and dry weight showed 491.9 cm²/plant and 2.68 g/plant, respectively, at 28 DAGU under 32 °C air temperature and 550 μmol·m⁻²·s⁻¹ light intensity. The changes of dry weight were rapidly increased under the higher air temperature and light intensity as followed by analysis of the growth curve. The beta distribution model was developed, and the relative growth rate (RGR) was simulated by the model, the maximum RGR was predicted at 0.116 g·g·d⁻¹. The RGR showed 0.113, 0.127, and 0.109 g·g·d⁻¹ at 10, 20, and 30 °C air temperature, respectively, and RGR was improved by 12% by increasing the air temperature by 10 °C, without going over 25 °C ADT. Results indicated that the developed growth model might be applied to optimal environmental control for maximized RGR of production of grafted hot pepper seedlings.

Since the first commercial vegetable seedling production business was established in the Republic of Korea in 1992, technologies for the production of vegetable grafted seedlings have been developed. Commercial grafting nurseries have promoted the efficiency of grafted seedling production by the selection and concentration strategy. At present, most scions and rootstocks are concentrated on one or two cultivars and all grafted seedlings are made by the splice grafting method. To overcome the disadvantages of the splice grafting method, such as delayed formation of the grafted union and delayed rooting, light-emitting diode (LED) healing chambers (LHCs) have been developed for enhancing grafted union formation, and are currently used in 20% of commercial grafting nurseries. The commercial grafting nurseries in Korea have been facing highly difficult situations because of climate change, increased seedling production cost and labor shortage. To confront this challengeable circumstance, it is essential to optimize grafted seedling production practices to produce high-quality seedlings at lower cost and low impact on the environment, and to ensure a consistent supply to vegetable growers year round. Here, we explored several practices to improve productivity and reduce the environmental impact of grafted seedling production, including the development of disease resistant or abiotic stress tolerant rootstock cultivars, the development of more precise and efficient facilities and cultivation systems such as a grafting robot, the application of a plant factory with artificial lighting, the improvement of light condition in LHCs, and wastewater reuse.

Irrigation scheduling and programming are very effective tools for efficient water use in a plant factory with artificial lighting (PFAL). In order to confirm optimal irrigation schemes for the production of cucumber scions and rootstocks in a PFAL, in this study, four different start points of irrigation were applied by measuring the weight of the plug tray to compare the growth of cucumber scions and rootstocks cultivated in a PFAL. Additionally, the growth characteristics of cucumber seedlings grafted with scions and rootstocks cultivated between in a greenhouse and in a PFAL were investigated. Although the growth of cucumber scions and rootstocks was highest when irrigation was conducted at 70% of water content in a medium, the growth of grafted cucumber seedlings before and after transplanting was not significantly different among the irrigation treatments in a PFAL. However, water use efficiency (WUE) during cucumber scions and rootstock production in a PFAL was higher at 60% than at 70%. Considering seedling growth and the efficiency of irrigation such as WUE and irrigation schedule, the optimal start point of irrigation during the production of cucumber scions and rootstocks in a PFAL was determined as 60% of water content in a medium. When the optimal irrigation regime was applied to the production of cucumber scions and rootstocks in a PFAL, the morphological characteristics of cucumber scions and rootstocks cultivated in a PFAL were more suitable for grafting compared with that of the cucumber scions and rootstocks cultivated conventionally in a greenhouse. The favorable environmental conditions during the cultivation of cucumber scions and rootstocks in a PFAL also positively affected the flowering response of cucumber grafted seedlings after transplanting.

To verify the productivity of the autotrophic transplant production method (ATPM), a novel propagation method in a plant factory with artificial lighting for transplant production (T-PFAL), strawberry transplants were produced by the ATPM for 365 days. A total of 3497 transplants were produced by the ATPM over 365 days with nine propagules in a cultivation area of 3.6 m² in the T-PFAL. When the simulated results were fit with the measured results, the propagation cycle timescales from planting propagules to producing the first, second, and third runner plants were 15, 27, and 43 days, respectively. The cumulative number of transplants (CNT) produced from 5, 10, and 20 initial propagules in a cultivation area of 36 m² over 365 days was simulated by the verified program along with the propagation cycles, and these values were 27,970, 30,010, and 31,900, respectively. The simulated CNTs from nine initial propagules in 18 and 72 m² over 365 days were 15,950 and 55,940, respectively. These results indicate that the ATPM is an appropriate propagation method to produce transplants rapidly in a T-PFAL, especially when the number of propagules or propagules is limited.

서 론