Dwarf tomatoes are advantageous when cultivated in a plant factory with artificial light because they can grow well in a small volume. However, few studies have been reported on cultivation in a controlled environment for improving productivity. We performed two experiments to investigate the effects of photosynthetic photon flux density (PPFD; 300, 500, and 700 μmol m⁻² s⁻¹) with white light and light quality (white, R3B1 (red:blue = 3:1), and R9B1) with a PPFD of 300 μmol m⁻² s⁻¹ on plant growth and radiation-use efficiency (RUE) of a dwarf tomato cultivar (‘Micro-Tom’) at the vegetative growth stage. The results clearly demonstrated that higher PPFD leads to higher dry mass and lower specific leaf area, but it does not affect the stem length. Furthermore, high PPFD increased the photosynthetic rate (Pn) of individual leaves but decreased RUE. A higher blue light proportion inhibited dry mass production with the same intercepted light because the leaves under high blue light proportion had low Pn and photosynthetic light-use efficiency. In conclusion, 300 μmol m⁻² s⁻¹ PPFD and R9B1 are the recommended proper PPFD and light quality, respectively, for ‘Micro-Tom’ cultivation at the vegetative growth stage to increase the RUE.

In Japan, red perilla leaves are used in the food and coloring industries, as well as in crude medicine. Perilla leaves contain a high concentration of phytochemicals such as perillaldehyde (PA) and rosmarinic acid (RA). The effects of UV-B radiation intensity (0.05–0.2 W m⁻², UV-B_BE: 0.041–0.083 W m⁻²), duration (3 or 6 h), and irradiation method (continuous or intermittent) for artificial nocturnal lighting using UV-B fluorescent lamps were evaluated on growth, flowering, and leaf phytochemical concentration in greenhouse-grown perilla. Under continuous UV-B irradiation at 0.1 W m⁻² for 3 or 6 h, leaf color changed from red to green and leaf fresh weight decreased, compared with the control treatment. No leaf color change was observed under the 3-h treatment with UV-B radiation at 0.05 W m⁻², wherein leaf fresh weight was similar to that of the control. Furthermore, RA concentration under continuous UV-B irradiation at 0.05 W m⁻² for 3 h increased two-fold compared to that under control treatment, while PA concentration was not affected by UV-B irradiation. Thus, our data showed that continuous UV-B irradiation at 0.05 W m⁻² for 3 h could effectively produce RA-rich perilla leaves without reducing in phenotypic quality or productivity. However, a 6-h intermittent illumination inhibited flowering without altering phytochemical concentration.

In this study, we developed an automatic irrigation method using an image-based irrigation system for high-quality tomato production in a greenhouse by investigating effects of a diurnal periodic cycle of irrigation on the photosynthesis, growth, yield, and fruit quality of tomatoes. The diurnal periodic cycle in a moderate wilting–full recovery treatment (MR) with a medium threshold value was more frequent than that in a severe wilting–full recovery treatment (SR) with a high threshold value. Mean daily maximum wilting ratios for MR and SR were 7.2% and 11.3%, respectively, when wilting ratios were set to threshold values of 7% and 14%, respectively. Total irrigation amounts in MR and SR were similar and lower than that in the untreated control. Net photosynthetic rate decreased under water stress, with values in MR being higher than that in SR, and recovered rapidly to more than 90% of its maximum value following irrigation. Plant growth and fruit yield per plant in MR and SR were lower than that in the control. Water stress treatment could improve fruit quality when it commenced at the anthesis stage or early fruit development stage. Total irrigation amount was a more important parameter than the threshold value for controlling the growth, yield, and fruit quality of tomatoes.

In this study, we investigated the effect of UV-B irradiation 3 days prior to harvest, on the accumulation of rosmarinic acid (RA) and anthocyanin, and the expression of genes related to phenylpropanoid and flavonoid biosynthetic pathways, in red perilla (Perilla frutescens L.). In experiment 1, seedlings at 60 days after sowing (DAS) were subjected to UV-B irradiation at 0 (control), 6, and 10 W m⁻² under a 16 h light period; while in experiment 2, seedlings at 45 DAS were subjected to UV-B irradiation at 0 (control), 4 W m⁻² at continuous irradiation, and 6 W m⁻² at 16 h irradiation. UV irradiation of 10 W m⁻² for 16 h negatively affected leaf color, while irradiation at 6 W m⁻² enhanced RA biosynthesis and antioxidant capacity. Continuous UV-B irradiation of 4 W m⁻² increased the RA concentration by 92% compared to the control; however, this effect was smaller than that of UV-B irradiation at 6 W m⁻² for 16 h, 141% higher than that of the control and had a lower antioxidant capacity against UV-mediated ROS overproduction during the dark period. Results demonstrate that 6 W m⁻² of UV-B irradiation for 16 h is suitable for enhancing the RA concentration and content of red perilla.

The demand for high-quality tomatoes is increasing; however, their production requires skillful techniques. To develop an automated irrigation method for producing high-quality tomatoes in a greenhouse, we used an image-based irrigation system to study how a diurnal periodic cycle of wilting–partial recovery irrigation affects growth, yield, and fruit quality. Three irrigation treatments were performed: a control with sufficient irrigation and two water stress treatments (moderate and severe wilting–partial recovery treatments; MPR and SPR, respectively). The mean daily maximum wilting ratios for MPR and SPR were 8.1% and 13.2% at wilting-level setpoints of 7% and 14%, respectively. The total irrigation amounts in MPR and SPR were 75% and 59% of that in the control, respectively. The corresponding yields in MPR and SPR were 76% and 56% of that in the control, respectively. The Brix and acidity of fruits in MPR and SPR were 15% and 10% and 34% and 24% higher, respectively, than those in the control at the end of the experiment. Plant growth decreased with increasing water stress levels. Plant length, leaf area, and the number of leaves were more sensitive to water stress than other growth parameters. SPR could be an effective irrigation method to improve fruit quality, even at high-air-temperature periods in summer.

We investigated the effects of irrigation patterns combining severe wilting with complete (S_R) or incomplete recovery (S_IR) on the growth, photosynthesis, fruit quality, and yield using a photograph-based irrigation control system. The study was performed in winter with a single sufficient irrigation treatment as Control, S_R, and S_IR. The daily mean maximum of the wilting ratios (W) in the S_R and S_IR was 15.1% and 15.3%, respectively, when W was set at 14%. S_R had the lowest total irrigation frequency of the three treatments. The accumulated cumulative wilting ratio in S_IR was 1.6 times that in S_R. Under water stress, the net photosynthetic rate decreased (S_IR < S_R), rapidly recovering to 73% and 80% of the maximum values following irrigation, respectively. The total amount of irrigation, the plant growth, and the yield were the highest in the Control and those of S_R and S_IR were comparable. S_IR produced the highest-quality fruit. The recovery level affected the fruit quality when the threshold values were similar; therefore, S_IR is appropriate to produce high-Brix tomatoes in winter. Conclusively, the image-based irrigation system could precisely and reproducibly control the irrigation (the most important parameter affecting the growth, yield, and fruit quality of tomatoes) to improve the fruit quality.