The fresh fruit yield of tomatoes (Solanum lycopersicum L.) is determined by yield components and related traits. In a low-truss cultivation in Japan, there was no significant difference in light use efficiency between different planting densities and stages. Accordingly, dry matter production is described by a function of intercepted light: Total dry-matter production = light use efficiency × Intercepted light. Light interception is determined by leaf area index (LAI) and the light extinction coefficient in the plant canopy. The efficiency of dry matter production per unit of intercepted light, i.e., light use efficiency, is determined by not only the leaf photosynthetic rate but also light extinction coefficient. The higher yield of modern tomato cultivars in The Netherlands is due to the increase in total dry matter production of plants, not by an increase in dry matter partitioning to fruits. An increase in the photosynthetic rate and a decrease in the light extinction coefficient may result in an increase in light use efficiency among Dutch cultivars. The yield of greenhouse tomatoes in Japan has increased little since the 1980s. Recently, Japanese researchers have attempted to improve the yield using current Japanese cultivars. Elevation of CO₂ and fogging in a greenhouse improved the fresh fruit yield and total dry matter production in Japanese cultivars. However, the fraction of dry matter distribution to fruit in ‘Momotaro York’ was significantly decreased. The fruit yield was also improved by grafting the Japanese scion ‘Momotaro York’ onto Dutch rootstock ‘Maxifort’ (S. lycopersicum × S. habrochaites). The increases in yield and total dry matter production were mainly determined by the increase in light use efficiency.

Interspecific crossing among the subgenera Amygdalus (Prunus persica, P. mira, P. dulcis, P. ferganensis, P. kansuensis, P. davidiana), Prunophora (P. salicina, P. cerasifera, P. mume, P. armeniaca), and Cerasus (P. tomentosa, P. japonica) was performed to determine their cross-compatibilities. In the combinations of species belonging to the subgenus Amygdalus, high fruit set averages were demonstrated, excluding the results when P. kansuensis was used as a seed parent. The pollination of species belonging to Prunophora and Cerasus by those of Amygdalus resulted in very few seeds. In contrast, fruit sets of Prunuphora species pollinated by Amygdalus fluctuated by cross combinations. P. cerasifera and P. salicina, when used as seed parents, bore a few seeds, but P. armeniaca and P. mume bore no seeds when pollinated by Amygdalus species. The cross using P. tomentosa as a seed or pollen parent resulted in very few fruit sets. On the other hand, several seeds were obtained from the cross between P. cerasifera and P. japonica. The pollination of P. japonica by P. cerasifera, P. dulcis, and P. mume also led to a relatively high rate of fruit sets.

To improve the uniformity of emergence, the effect of the physical properties of a medium on the emergence of tomato was investigated. In experiment 1, tomato ‘CF momotaro york’ was sown in plug trays with 4 different medium conditions: bulk densities of a commercial medium made from mainly peat moss of 0.12 (PM/L) and 0.15 (PM/H), and bulk densities of granular rockwool of 0.14 (RW/L) and 0.28 (RW/H). When the plug trays were irrigated with different amounts of water, pF showed emergence rates at 4 days after sowing as follows: PM/L, 1.53; PM/H, 1.48; RW/L, 1.37; and RW/H, 1.58. In experiment 2, the seeds were sown in petri dishes at a depth of 5 mm in the same media as in experiment 1. The range of pF exceeding 90% of the germination rate at 72 h after sowing was: PM/L, 1.23~3.06; PM/H, 1.17~3.20; RW/L, 0.85~1.46; and RW/H, 1.40~1.87. In experiment 3, the water distribution in cells of plug trays with the 4 different medium conditions and different irrigation amounts was investigated. Under all conditions, pF of the top layer (depth of 0~1 cm) did not change between 1 and 48 h after irrigation. pF of the top layer in PM/L and RW/L stayed in a range with a germination rate exceeding 90% in experiment 2 regardless of the irrigation amount. The range of pF in cells 48 h after irrigation in experiment 3, corresponding to the maximum emergence rate in experiment 1, was: PM/L, 1.47~1.65; PM/H, 1.32~1.64; RW/L, 1.07~1.35. Water distribution in the medium was, therefore, necessary for improving the emergence rate at 4 days after sowing. pF in cells should be kept within the range of 1.4~1.6 to achieve a high germination rate.

Open-field vegetables are often damaged by incidents like short periods of heavy rain or typhoons, especially in the period from summer to autumn. To reduce the damage to such vegetables caused by flooding, we examined the effects of the duration of flooding (flood time), the period in which flooding occurred (flood period), varietal differences in waterlogging tolerance, and liquid manure irrigation after waterlogging on the growth and yield of lettuces. The effects of the flood period and time on lettuce growth were greater before head formation (leaf age 13); i.e., the head weight was significantly reduced by 12 hours’ flooding, and all lettuces died when the flood time was 24 hours. In contrast, the head weight was not affected by 12 hours’ flooding in the early phase of head formation (leaf age 18), but when flooding occurred during the period just before the harvest (leaf age 35) the quality of the lettuces was reduced by the presence of clay. Regarding the crop type, the ‘Hamming Chau’ variety, which is sown in late August, exhibited a high waterlogging tolerance, and its head weight was not reduced by waterlogging. As for methods that can aid recovery after waterlogging, liquid fertilizer composed of urea diluted 50 times with water (total amount: 50 L・a^–1) was given to lettuces that had been subjected to 6 hours’ waterlogging before head formation (leaf age 16) or during the early phase of head formation (leaf age 18). Compared with the lettuces that were not treated with urea after the waterlogging, the head weight and head volume of the urea-treated lettuces were 12 and 33% greater, respectively, being similar to the values of the non-waterlogged lettuces.

We investigated the effect of temperature change on pollen germination and pollen tube elongation in vitro, using the pollen of ‘Napoleon’ which is often used as a pollination tree. At two-stage variable temperatures, the elongation rate of the pollen tube decreased markedly immediately after changing the temperature from 20 to 4°C. Even when the temperature was returned to 20°C, the relative elongation of the pollen tube remained at 50% of the initial rate. Also, morphological abnormalities such as refraction and hypertrophy of the pollen tube tip were observed. When the temperature varied, germination was not observed, even after a lapse of 15 hours at 4°C. By changing the temperature to 20°C, the pollen tube elongated rapidly. The fruiting of sweet cherries depended on the temperature at the time of pollination. Good fruiting was achieved when pollination occurred between 10 a.m. and 2 p.m.; however, the fruiting rate was reduced with evening or early morning pollination when the temperature was lowered. When pollination occurred at 5 p.m., pollen tube extension was relatively favorable. However, morphological abnormalities in the pollen were observed.

The citrus cultivar ‘Setoka’ was selected from a cross between ‘Kuchinotsu No. 37’ (‘Kiyomi’ × ‘Encore’) and ‘Murcott’. Because of the excellent quality of this fruit, the growing area is increasing both in open fields and greenhouses. However, excessively softened fruit with a yellowish orange rind and poor taste are sometimes produced, particularly when cultivated in a plastic house. In this study, we examine the detailed differences in fruit quality between affected and normal fruit and the mechanism of the disorder. Compared with normal fruit, the affected fruit was smaller and had a thinner rind with lower a* value. The elasticity of the affected fruit determined by a texture analyzer was about 10% lower than that of normal fruit. Juice from the affected fruit had a markedly low sugar content; in particular, sucrose, which is the main sugar of ‘Setoka’, was 65% lower than that in normal fruit. The citric acid content of the affected fruit was 27% higher, and the total amino acid content was 35% lower than that of normal fruit. The average incidence of affected fruit was 3.1%; in particular, the incidence in the inner canopy was 11.8%, which was higher than that in other parts. A tracer experiment with ¹³C showed that the translocation of photosynthates to the fruit was markedly restricted in the affected fruit. The accumulation of callose was microscopically observed in the phloem of the affected fruit disc, suggesting that an obstruction of the sieve tube by callose prevents the translocation of photosynthates to the fruit and results in a lower sugar content.

To develop a low-tree-height apple cultivation technique using a flat trellis system, large-sized nursery stocks of the apple cultivars ‘Fuji’, ‘Tsugaru’, and ‘Koukou’ with Marubakaido rootstock were planted under a 1.8- m- high flat trellis in 2004, at a density of 400 plants ha^–1. They were then grown and trained following an H-shaped pattern for 9 years, with fruit yield and quality evaluated annually. It was found that apple trees under the flat trellis system were high yielding in the first years compared with those under the conventional open center training system, because the fruit yield of the three varieties exceeded local average productivity (22 t・ha^–1) in the fifth or sixth years after planting, and two of them met local target productivity (35 t・ha^–1) in the ninth year. However, the average yield of each variety from the seventh to ninth years was 71–81% of the target productivity, which was lower than that of the adult trees under the open center training system. The fruit weight and soluble solids content of each variety increased annually, and fruits grown under the trellis system became larger than those grown under the open center training system, with soluble solids contents greater than 13° or 14° at the end of the study. A high number of water sprouts, however, emerged on trees under the flat trellis system, which led to a lower number of flower buds, particularly on the lateral shoots near the main stem, despite pinching and summer pruning being conducted. The decreased number of flower buds further resulted in a reduced fruit yield in the following years, therefore, the cultivation system used in this study should be improved to reduce water sprout emergence.

Boiled green spinach leaves become bleached when exposed to light. To increase knowledge about such color change by photobleaching, the appearance and chemical components of 48 spinach cultivars were examined under different cultivation conditions. Although marked varietal differences in the growth rates and Brix and ascorbic acid contents were observed among the cultivars used, these factors were not related to the depth of leaf color. The chlorophyll content was significantly correlated with the depth of leaf color under some cultivation conditions. Varietal differences in the sensory evaluation of leaf color were stable under some cultivation conditions. The leaf color was deeper and more desirable following wintersweet treatment, although the chlorophyll content did not change. Such a deeper color of wintersweet-treated spinach could be due to its thicker leaves, which increased the chlorophyll content per unit area. The color of boiled leaves exposed to light was significantly correlated with that of raw leaves. The cultivars with higher h and lower C* and L* values were evaluated as having a desirable deep green color when both raw and boiled. The cultivars with a deep color when raw retained their color after boiling and photobleaching. Therefore, the color of raw spinach leaves is the most important factor in determining color after boiling and photobleaching. Brix and ascorbic acid contents increased following wintersweet treatment. This treatment is important to obtain spinach with desirable color and chemical components.

Leucocoryne is a geophyte belonging to the family Amaryllidaceae, and it is native to Chili. When cultivared in Japan, leucocorynes usually bloom in spring, and their bulbs show long-term dormancy during summer (> 6 months). Therefore, leucocryne growers desire to shorten the dormancy duration for early flowering. Here, we studied the relationship between the storage temperature and its period for dormancy break of bulbs, bud emergence, flowering, and flower quality in leucocorynes. When their bulbs were stored at 25–35°C for over 8 weeks, uniform bud emergences was observed in 95–100%. Similarly, days to anthesis from planting were also shortened by 50 days compared with non-storage bulbs. However, a cumulative temperature exceeding at 1,500°C・day during the storage period was not effective to further shorten flowering. These bulb storage treatments led leucocorynes to early flowering without reducing the flower quality. We demonstrated a new leucocoryne cropping type that resulting in blooming from November to December, when bulbs were stored at 30–35°C for 8 weeks and then grown at 15°C.

Wasabi has been part of the Japanese diet for centuries, however, young people may be rejecting the traditional Japanese diet. In this study, we investigated whether the avoidance of wasabi in young people is an actual phenomenon using postal questionnaire surveys involving students in 15 agricultural high schools and residents in 3 senior care homes. Responses were obtained from 259 young students and 53 elderly people. A significantly higher rate of young students disliked wasabi compared with elderly subjects. A significantly higher rate of young female students disliked wasabi compared with young male students; the main reason was that female students experienced nasal irritation their noses stung after consumption. There was also a tendency for young students who liked wasabi to prefer fish to meat and to come from families that ate wasabi. The home environment was considered an important determinant of the preference. A previous study involving Korean and Japanese subjects, suggested a significant correlation between pungency preference and wasabi preference. The tendency to avoid wasabi and yet eat red pepper cannot be ignored if Japanese food culture is to survive. It is necessary to increase the opportunities for young Japanese people to eat raw wasabi

The educational effectiveness of internship at horticultural production sites on high school students who are learning horticulture was investigated through text mining analysis based on an internship report and self-assessment questionnaire. In the hierarchical cluster analysis and co-occurrence network, the four expected educational effect items indicated by the Ministry of Education, Culture, Sports, Science, and Technology were obtained through the internship in this program. The results of the self-assessment questionnaires revealed that students took the internship seriously, and developed work-related awareness; further, the knowledge, skills, and interests in agriculture of the students increased. Therefore, internship at horticultural production sites is an effective educational strategy to train high school students learning horticulture in terms of promoting professionalism, motivation to learn, and the acquisition of knowledge and skills.

The genus Paphiopedilum within Orchidaceae has undergone various breed improvements, resulting in various complex hybrids with large, colorful, and round flowers. In the present study, the breed improvements of the complex hybrids of white flowers of the genus Paphiopedilum were assessed based on the sizes of Japan Orchid Growers Association prize-winning flowers between 1981 and 2015. During the past 30 years, the natural spread width (NSW) and petal width (PW) have increased by about 15 mm, while PW/NSW has increased by about 0.1, demonstrating breed improvements (larger and more rounded varieties) of the complex hybrids of white flowers. Furthermore, such breed improvements have markedly advanced since around 2000. Of note, the progenies of Paph. Skip Bartlett have greatly contributed to the improvements. In the future, breeding will be promoted by crossing these varieties as parents.

For farmers to inoculate seedlings with attenuated virus easily we examined an inoculation method using an irrigating device as a simple sprayer. Experiments were conducted using cucumber ‘Excellent fushinari No. 2’ and the attenuated Zucchini yellow mosaic virus (ZYMV) water-soluble powder. We investigated the rate of infection by the attenuated ZYMV under conditions that consisted of two sizes of carborundum (600 and 1200 mesh) combined with two treatments of carborundum (mixed inoculum and dusted cotyledons). As a result, we could inoculate more effectively by spraying the inoculum on 600 mesh carborundum-dusted cotyledons. In addition, we obtained a stably high infection rate (72%) on spraying at a distance of 10–17.5 cm from the cotyledon. On the other hand, the susceptibility to the attenuated ZYMV using a rubbing-based inoculation method was tested among six varieties of cucumber including ‘Excellent fushinari No. 2’, showing that the susceptibility differed among the six varieties.

Delphinium grandiflorum cut flowers of the summer-to-autumn culture in Hokkaido have unfavorable characteristics, such as a short stem length and few lateral branches. In the present study, the effects of short-day and night chilling treatments on D. grandiflorum seedling growth were investigated to improve the cut flower quality. Delphinium grandiflorum ‘Super Grand Blue’ and ‘Super Platinum Blue’ were treated with combinations of short-day (9-h light period) and night chilling (10°C) conditions using a spot air-conditioner for 35 days until planting. Under the combination of short-day and night chilling treatments, the cut flower lengths were the longest and the number of lateral branches was the highest in both cultivars. The short-day treatment had stronger inhibitory effect than the night chilling treatment on the shift from vegetative to reproductive growth. Moreover, when ‘Super Platinum Blue’ was treated with night chilling at 9, 12, 15, and 18°C under the short-day condition, the cut flower length was the longest and the number of lateral branches was the highest at 9°C. The cut flower length did not differ between the temperatures of 12°C and higher, whereas the number of lateral branches decreased with higher temperatures. These results indicate that culturing D. grandiflorum seedlings under the short-day (9-h light period) and night chilling (10°C) conditions is an effective way to improve the cut flower quality of the summer-to-autumn culture in Hokkaido.