Joon Kook Kwon

Yield loss and quality degradation of strawberry fruits cultivated under the deficient insolation conditions by shading

Deficient insolation conditions (DICs) frequently occur during the winter and early spring season in Korea and negatively affect crop growth. This study was conducted to investigate changes in the yields and qualities of strawberry fruits under DICs that result from an insufficient input of sunlight. To induce DIC, strawberry plants were treated with 40 or 70% shading by covering the plants with curtains during growth in a plastic greenhouse. The shaded plants were cultivated from March to May of 2012. When the strawberry plants were subjected to the shading treatments, their photosynthesis and fruit yields were significantly reduced. Although the mineral element and organic acid contents of the fruits were not affected by the shading treatments, the total nitrogen (T-N) of the stems and roots were noticeably reduced. Furthermore, the shading treatments of the plants also resulted in reductions in the sugar contents and total phenolics of the fruits. In parallel with these observations, the shading treatments were also found to decrease the antioxidant activities of the fruits as measured with the DPPH assay. We suggest that the DIC-induced losses of strawberry fruit yield resulted from the reduced photosynthetic performances of the plants that were caused by insufficient sunlight.

Development of a coupled photosynthetic model of sweet basil hydroponically grown in plant factories

For the production of plants in controlled environments such as greenhouses and plant factories, crop modeling and simulations are effective tools for configuring the optimal growth environment. The objective of this study was to develop a coupled photosynthetic model of sweet basil (Ocimum basilicum L.) reflecting plant factory conditions. Light response curves were generated using photosynthetic models such as negative exponential, rectangular hyperbola, and non-rectangular hyperbola functions. The light saturation and compensation points determined by regression analysis of light curves using modified non-rectangular hyperbola function in sweet basil leaves were 545.3 and 26.5 µmol·m-2·s-1, respectively. The non-rectangular hyperbola was the most accurate with complicated parameters, whereas the negative exponential was more accurate than the rectangular hyperbola and could more easily acquire the parameters of the light response curves of sweet basil compared to the non-rectangular hyperbola. The CO2 saturation and compensation points determined by regression analysis of the A-Ci curve were 728.8 and 85.1 µmol·mol-1, respectively. A coupled biochemical model of photosynthesis was adopted to simultaneously predict the photosynthesis, stomatal conductance, transpiration, and temperature of sweet basil leaves. The photosynthetic parameters, maximum carboxylation rate, potential rate of electron transport, and rate of triose phosphate utilization determined by Sharkey’s regression method were 102.6, 117.7, and 7.4 µmol·m-2·s-1, respectively. Although the A-Ci regression curve of the negative exponential had higher accuracy than the biochemical model, the coupled biochemical model enable to physiologically explain the photosynthesis of sweet basil leaves.

Effects of foliar fertilization containing titanium dioxide on growth, yield and quality of strawberries during cultivation

We addressed the question of whether it is useful to apply a titanium dioxide (TiO2) solution to promote the growth of strawberry plants in a greenhouse when they suffer from insufficient solar radiation during the winter season. A TiO2 solution was sprayed on strawberry plants three times during the growth period. This treatment occurred once on the 5th day of each month from December to February at concentrations of 50, 100 or 150 mg·kg -1. The control strawberry plants were treated with a foliar solution lacking TiO2. The length of the petiole was inhibited by TiO2 treatments, especially those in January and February. In terms of the fruits, the TiO2 applications were found to increase the yield and hardness of strawberries compared to the control. In addition, the contents of chlorophyll a and b in the leaves of the strawberries were increased by the treatment with TiO2 foliar spray. In contrast, the phenolic compounds of the fruits were decreased as a result of the TiO2 treatments. Combined, our results reveal that the application of TiO2 can promote the yield and quality of strawberry plants sufferings from a shortage of sunlight in a plastic greenhouse during the winter season.

Optical Characteristics of Two New Functional Films and Their Effect on Leaf Vegetables Growth and Yield

Three leaf vegetables, namely green lettuce, red lettuce (Lactuca sativa) and red-veined chicory (Cichorium intybus) were grown in minigreenhouses covered with two new functional films and conventional polyethylene film (PE). Seedlings of leaf vegetables were transplanted in a plastic troughs filled with soil-perlite mixture. Two functional films were made from polyolefin (PO) material. Measurement of optical characteristics showed that polyolefin films have better transmittance for the photosynthetic active radiation (PAR, 400-700nm) and higher absorptance for the ultraviolet radiation (UV, 300-400nm) in comparison with the conventional PE film. After three months of utilization higher loss in PAR transmittance was observed for conventional PE film. Leaf vegetables growth was enhanced and yield was increased in greenhouses covered by new functional films.

Effect of monochromatic UV-A LED irradiation on the growth of tomato seedlings

Effect of 376 nm UV-A LED irradiation on the growth and morphology of tomato seedlings was studied. Tomato seedlings were grown under the 658 nm red LEDs or the red LED supplemented with two irradiation levels of the UV-A. The growth and development of tomato seedlings were significantly enhanced under the red light supplemented with the UV-A. Under the UV-A treatments, the tomato seedlings became more compact, the growth of plant organs was balanced, the leaf area was increased, and the total plant fresh and dry weights were also enhanced. Our findings suggested that the 376 nm UV-A from LEDs had a beneficial effect on the growth and development of tomato seedlings as similarly to the blue light.