The purpose of this study was to clarify the plant growth and fruit quality of blueberry in a controlled room under artificial light. Cultivars used were a northern highbush 'Blueray', and two southern highbush, 'Misty' and 'Sharpblue'. A comparative study was carried out of growth characteristics, photosynthetic potential and fruit quality analysis in different growing environments, in particular focusing on plants growing in a glasshouse under natural sunlight and plants in a controlled room under artificial light. Environmental conditions of the controlled room under artificial light were 15 to 25°C, 50 to 70% humidity, 150 to 350 μmol·m −2 ·s −1 light intensity, and a 10-hour photoperiod from the primary experiment. In these growing environments, normal fruits developed from all the tested cultivars by successful growth without decreasing plant vigor and leaf photosynthetic ability until fruit harvesting time compared to the cultivars grown in the glasshouse under natural sunlight condition. Moreover, it was confirmed that high-quality fruits could be harvested in a controlled environment to increase fruit production with high SSC % and high anthocyanin content but low acid % in 'Blueray' and 'Misty', but not 'Sharpblue'. Finally, this report presents the possibility of high-quality blueberry production in a controlled environment under artificial light conditions with some cultivars.
To clarify the response of net photosynthetic rate (Pn), stomatal conductance (gS), transpiration rate (Tr), and leaf intercellular CO2 concentration (Ci) to irradiance on the adaxial and abaxial sides of mature and young strawberry leaves using blue, green, and red light-emitting diodes (LEDs), irradiation from a short distance was investigated using ‘Tochiotome’. Light–photosynthetic response curves of the adaxial side of mature leaves were not different among LED treatments. However, those of the adaxial side of young leaves irradiated with red LEDs were less than those of other LED treatments. Pn of the abaxial side of mature leaves was 42% to 71% of the abaxial side. In young leaves, Pn of the abaxial side was 17% to 68% of the adaxial side. Moreover, light–transpiration response curves were different with LED treatments. Ci and Tr under blue and green LEDs were greater than those under red LEDs. This indicates that blue and green lights affected the stomatal opening. In contrast, red LEDs decreased Ci more than other LED treatments. In addition, reactions of the adaxial side of young leaves under blue and red LEDs were seen not only in ‘Tochiotome’, but also in ‘Sachinoka’ and ‘Eran’, which indicates that the photosynthetic reactions of blue light and red light are common characteristics of the strawberry. Therefore, red LEDs promoted the photochemical reaction and activated the CO2 fixation system. Based on the results of this study of short-distance lighting with LEDs in strawberry production, irradiance of the abaxial side of leaves by blue or green LEDs might improve more assimilates in young leaves compared with red LEDs to increase strawberry yield.
We attempted to shorten the juvenile phase of southern highbush blueberries by using controlled rooms under artificial light. Seeds were extracted from fresh fruits and sowed in the Woody Plant Medium (WPM) immediately after harvest. When these seeds were irradiated with red LED, their germination rate was over 80% by the 35 days after sowing. The seedlings in the controlled room continued to grow without entering the dormant phase. Especially, maximum growth was observed under the long-day condition of 12-h light. Even under the short-day condition of 8-h light, increased growth was observed when grown at a high light intensity (400 μmol·m for the entire length of the experiment, the flowering of 'Misty' seedlings was observed within 300 days after sowing. The seedlings maintained under the short day condition of high light intensity flowered earlier than seedlings moved from the long-day controlled room to the short-day controlled room. Thus, southern highbush blueberries were successfully induced to flower in less than a year from seed planting, using a combination of techniques to promote germination and control the growth environment conditions in a controlled room.
Photosynthetic characteristics measured with the leaves of 'Weymouth' highbush blueberry (Vaccinium corymbosum L.) and 'Tifblue' rabbiteye blueberry (V. ashei Reade) in phytotron were compared with regard to their responses to light intensity (0-2,000 µmol・m −2 ・s −1 ) and temperature (15-35°C). As temperature increased, photosynthetic rates of both cultivars increased.Photosynthetic rates of 'Weymouth' were higher than those of 'Tifblue' under low temperature conditions (15-20°C). However, there was no difference in photosynthetic rates measured under high temperature conditions (25-35°C), but 'Weymouth' showed higher transpiration rates and lower water use efficiencies (WUE) than 'Tifblue'. Furthermore, photosynthetic characteristics of 'Blueray' highbush blueberry under high temperature conditions (28 and 35°C) were similar to those of 'Weymouth' under high temperature conditions. These findings show that photosynthetic characteristics of leaves could be related to the suitability of highbush blueberries to cool conditions, and to the heat tolerance and drought resistance of rabbiteye blueberries. WUE values measured at high temperature >35°C and high light intensity >1,000 µmol・m −2 ・s −1 could be helpful as indices for evaluating and selecting blueberry plants with heat tolerance. Transpiration rates increased at high temperature and high light intensity, which suggested that shading in summer to control light intensity under 1,000 µmol ・m
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