Sensitivity to ethylene of cut snapdragon (Antirrhinum majus L. cv. Yellow Butterfly) flowers and the effects of pulse treatments with either silver thiosulfate complex (STS), sucrose or in combination on vase life were investigated. Exposure to ethylene at 2 and 10 μL L⁻¹ for 48 h induced abscission of petals in cut flower spikes, suggesting that snapdragon flowers are moderately sensitive to ethylene. Cut snapdragon spikes were treated with 50, 75, 100 and 125 g L⁻¹ sucrose with or without 0.2 mM STS for 24 h. Treatment with STS alone slightly extended the vase life of cut flowers, but treatment with sucrose alone extended the vase life of cut flowers only with increasing concentration of sucrose up to 100 g L⁻¹. Treatment with STS plus sucrose was more effective in promoting floret opening and extending vase life than that with sucrose alone at all sucrose concentrations tested. The size of florets opened after harvest was greater for treatment with sucrose alone or STS plus sucrose treatments than in control or STS alone treatments. Concentrations of aurones, pigments responsible for yellow color in the petals, were higher for treatment with sucrose or STS plus sucrose than in control or STS alone treatments. Soluble carbohydrate concentration in the petals was highest for treatment with sucrose, followed by STS plus sucrose, whereas it was lowest in STS treatment. These findings suggest that pulse treatment with STS plus sucrose is the most effective for extending vase life of cut snapdragon flowers and for improving pigmentation.

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The goal of this study was image segmentation between crop and weed using hyperspectral imaging for weed detection. This technique is useful for selective weeding using spot spraying or a robotic system. A hyperspectral image consists of a large number of pixel spectra. Therefore, image segmentation was executed pixel by pixel. After each pixel spectrum was extracted from the image, it was identified as soil or plant. If the pixel spectrum was identified as plant, it was categorized as crop or weed. For the pixel discriminant model between soil and plant, simple NDVI thresholding was employed. The pixel discriminant model between crop and weed consisted of normalization, generation of explanatory variables and discrimination, and four types of models were developed and validated. Finally, segmented images between crop and weed were generated from the hyperspectral images by applying these models. As the validation results, pixel discrimination between soil and plant was performed with 99.9%. Also, most pixel discriminant models between crop and weed had a success rate of more than 90%. As a result of image segmentation between crop and weed, most hyperspectral images were segmented correctly. This study demonstrated the possibility of weed detection using hyperspectral imaging.

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Time domain reflectometry (TDR), measuring the travel time of a microwave signal, has been recognized as a superior method of monitoring volumetric water content (θ) in soil. Although various custom-designed TDR probes having different advantages have been designed, the calibration requirement for any specific probe has been a major problem for their users. To propose a simpler calibration approach for custom-designed probes, we first examined their sensitivity to the change in permittivity for several fluid media (air, water, and ethanol-water mixtures), and then calibrated them for sand with a different θ. The custom-designed probes were less sensitive to the change in permittivity than a conventional probe because the detection part is surrounded by low-permittivity materials, and thus we could not adequately determine θ of sand from measured permittivity by applying widely used Topp equation. However, we confirmed that the equation is valid for estimating θ if the effect of the surrounding materials on the measured permittivity was excluded, which effect can be evaluated based on the data sets of permittivity measured for the fluid media. From this result, we concluded that the calibration of the custom-designed probes can be easily conducted by the testing for the fluid media.

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A new airflow system with multi-fan for precise airflow control and its evaluating method were suggested. A computational fluid dynamics (CFD) simulation was employed to analyze airflow. A cultivation space (1.0×1.0×0.5 m³) was established in the CFD model, and 12 lettuce models with simplified shapes were set in the space. Six small fans were used for generating airflow in the model. In order to verify the accuracy of the CFD model against the actual situation, the same situation as the CFD model were prepared. Lettuce replicas were made of steel meshes with sealing tapes. The accuracy of the CFD model was enough to investigate performances of the airflow control patterns. We assumed that the net photosynthetic rate per plant can be calculated the summation of the net photosynthetic rate calculated with the air current speed and the leaf area in the cell (the minimum unit of the CFD model) on the surface of the lettuce models which were the adjacent cells to the lettuce models. The suggested airflow control pattern could provide more uniform airflow distribution than the conventional airflow pattern and also enhance the net photosynthetic rate more than that in the conventional airflow pattern with the same energy input.

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A simulation model was developed for heterologous protein production in transgenic lettuce. The model focused on the time course of fresh weight and heterologous protein of each leaf. The total amount of heterologous protein in a head of lettuce was expressed by the summation of all amounts of heterologous protein in all leaves. Soluble rather than heterologous protein concentration was used due to the unavailability of the transgenic lettuce producing specific heterologous protein. The parameters of the model were decided based on lettuce (Lactuca sativa L. cv. ‘Greenwave’) grown in the plant factory at Osaka Prefecture University. The first simulation reproduced the time course of soluble protein production in a head of lettuce grown under conventional environmental conditions. In the second simulation, protein production at 15°C and 25°C was simulated to investigate the effect of the model parameters on protein production. The results indicated the existence of an optimum cultivation cycle and the advantages and disadvantages of protein production at low and high temperature.

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We determined the role of phenolic metabolism in promoting shoot regeneration in vivo by shading cut surfaces of tomato stems. The number of regenerated shoots from shaded stems was significantly increased (36.2) compared with unshaded stems (18.2). The concentration of phenols in shaded stems during 7–28 days after cutting was lower than that in unshaded stems, and decreased to concentrations lower than initial levels during the experimental period. The activity of phenylalanine ammonia-lyase (PAL) in unshaded stems was higher than that in shaded stems and fluctuated, whereas PAL activity in shaded stems stably remained at a lower level than the initial level. Neither polyphenol oxidase activity nor peroxidase activity were affected by shading. As the result, shading induced suppressed PAL activity and a lower concentration of phenols in the cut stems of tomato plants, and increased the number of regenerated shoots.

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