Simplified equipment for low-humidity treatment (LHT) was developed by installing a light source and heaters in a small refrigerator. Then, LHT was applied to rootstock squash (Cucurbita moschata Duch.) seedlings for 24 h before they were cut and cucumber scions grafted onto them. Average air temperature, relative humidity, and vapor pressure deficit in the LHT equipment were 30°C, 15%, and 3.6 kPa, respectively. Dry weight and percent dry matter of the rootstock shoot at end of LHT were significantly higher than those of seedlings grown in a greenhouse at a temperature of 15/29°C (night/day) and vapor pressure deficit of 0/2.2 kPa (night/day) instead. Leaf conductance of the seedlings that received LHT was 0.39 times that of those not receiving LHT. Grafted cuttings were obtained by grafting cucumber scions onto the squash rootstock receiving or not receiving LHT. The grafted cuttings were planted in growth medium and then grown for 7 days in a plastic-film tunnel. Total fresh weight, root fresh weight, and root number of the plants grafted onto the rootstock that had received LHT were 1.14, 1.36, and 1.44 times those of plants grafted onto rootstock not receiving LHT. LHT apparently enhanced the growth after planting by causing a decrease in the transpiration rate of the rootstock, as reported previously. A similar experiment, conducted under artificial lighting, showed similar results for percent dry matter, leaf conductance, and root fresh weight after planting.

View full abstract

As there are currently many large-scale production facilities that have contracts with the large retailing companies, accurate prediction of yield is necessary. The present study developed a method to predict tomato yield accurately using the data on the outside solar radiation. The present study was conducted in a Venlo-type greenhouse (29,568 m²) at Sera Farm Co., Ltd. in Sera-cho in Hiroshima prefecture. The cultivar used for this experiment was plum tomato. The sowing took place on July 18, the planting took place on August 30, and the harvesting started on October 9, 2002. The planting density was 2.5 plants·m^-2. As the results of the analysis of correlation between the weekly tomato yield and the integrated solar radiation for the period from October 7 to July 28 (43 weeks), the highest correlation (r=0.518) between the weekly tomato yield and the solar radiation integrated from seven to one weeks before the harvesting was observed. Further investigation by the same correlation analysis was conducted for the 25 weeks period from December 8 to May 26, during which time the effect of growing stages and air temperature were considered to be relatively small. The results showed the highest correlation (r=0.730) between the weekly tomato yield and the solar radiation integrated from eight to one weeks before the harvesting. The tomato yield occasionally needed to be adjusted at Sera Farm. Consequently, the correlation between the three-week moving average of tomato yield and the integrated solar radiation was calculated. The results showed the highest correlation was obtained for the period from eight to one weeks before the harvesting (r=0.860). This study therefore showed that it was possible to predict the tomato yield(y: kg·m^-2·week^-1) using the following equation on the solar radiation integrated from eight to one weeks before the harvesting(x: MJ·m^-2): y=7.50×10^-6x+0.148 (r²=0.740).

View full abstract

We have been conducting research on the improvement of productivity in large-scale greenhouse tomato production. One of the factors that largely influence the tomato productivity is the rate of CO₂ fixation by photosynthesis. The amount of CO₂ fixed by the whole plant canopy varies considerably and is known to depend on canopy structure.
To date, few studies have analyzed photosynthesis in plant canopies within the context of improving productivity for large-scale tomato production. Consequently, obtaining data and developing analytical methods that are relevant to production is important.
The present study investigated the rate of photosynthesis within a plant canopy and the vertical distribution of the amount of CO₂ fixed by plants with the aim of increasing CO₂ fixation and yield. This was done by analyzing the photosynthetic rate in individual leaves, examining plant canopy structure and measuring light intensity within the plant canopy.
It was found that the leaves located in the upper parts of canopies were exposed to higher light intensities, experiencing light saturation and had higher rates of photosynthesis at the point of light saturation than leaves in the middle and lower parts of the plant. It was assumed that this was due to the occurrence of senescence and the development of shade-leaf characteristics in the leaves of the lower parts of the plant. The results implied that removal of the leaves under 150 cm or farther from the apical meristems could increase CO₂ fixation and productivity of the plant canopy.
The analytical methods developed in the present study can be applied to assess the efficacy of seasonal management methods such as cropping patterns, utilization of lateral buds, and leaf thinning, for maximizing yields.

View full abstract

The flower bud formation and development of ‘Kawazu-zakura’ cherry (Prunus lannesiana Wils.) was investigated in the Izu peninsula. By the beginning of July, the floral primordium had already been formed. Afterward, the calyx lobe was formed at the beginning of September, the petal at the beginning of October, and the stamen in the middle of October.
During late November, the ovule was formed. After the petal was formed, the difference in floral bud formation was confirmed by the year and place. After the flower bud was completed, the growth of the floral bud was classified into eight stages in externals. The influence of the average temperature was suggested in floral bud formation. Buds in which green seems to crack require even, full-blooming on 32 days or more. One bud kept flowering for 14 days or more. We confirmed that floral buds with different stages existed together on the same observation day. It was thought that the flowering period of ‘Kawazu-zakura’ was long because the flowering period of one floral bud was long, and floral buds in a different state flowered continuously.

View full abstract

This study is aimed at the development of a novel device for the physical control of insect pests by utilizing various characteristics of a high-luminance yellow LED, in place of agricultural chemicals when targeting hard-to-control insect pests, such as common cutworms and cotton ballworms (noctuidae family) that can ravage agricultural crops. Initially, the wavelength dependency and self-regulated power spectrum of the electro-retinogram (ERG signal) of the target insects were measured in terms of various photo stimuli. Then, based on the response characteristics of the ERG signals obtained from the experiments, an LED light source device was fabricated and was installed in the field. Finally, the effectiveness of the device in controlling insect pests is discussed, based on the investigation of the inhibiting effects on mating behavior estimated from the number of insect pests counted on cabbage plants in a test area, as well as verification of the photo taxis of the insects.

View full abstract