Here, we describe the current status of energy-saving techniques in greenhouse heating and countermeasures for high summer temperatures, and then introduce an outline and the performance of a newly developed New Root-zone Environmental Control System (N.RECS) and the effects of this system on flower production. Temperature control techniques used in protected horticulture include those that control the air temperature of the entire greenhouse space and those that control the local temperature of the plants. The running costs of the air temperature control techniques are expensive and the cooling capacity in the summer are inadequate for actual cultivation. Local temperature control techniques have relatively low running costs and can adequately cool plants during high temperature periods, but they are crop-specific and not versatile. Therefore, we developed a N.RECS that can heat and cool the root-zone of various plants with low running costs. N.RECS was produced by combining aluminum heat exchange panels, insulated pot trays and an air-source heat pump cold/hot water supply system. By using N.RECS, the root-zone temperature was maintained at 25°C when the air temperature was about 5°C during the winter and cooled to below 23°C when the air temperature was about 35°C during the summer. Root-zone heating of six potted flowers and cut flowers in the winter promoted growth and flowering and achieved energy savings of about 30% compared to conventional heating.
When the two flower species, which are susceptible to high temperature, were grown under high temperature conditions, about half of the plants died, but root-zone cooling allowed all the plants to grow healthily. Therefore, it is concluded that N.RECS is a practical system that allows for both energy-saving cultivation in the winter and cooling cultivation in the summer. In addition, root-zone temperature is an environmental control parameter that should be controlled in future agricultural production; by applying root-zone temperature control as a standard technology for agricultural production, the growth of plants can be controlled more flexibly and more energy can be saved.
To improve the yield of sweet peppers in Japan, we investigated the relationships between plant growth characteristics and fruit yield, with a particular focus on dry matter production. Fruit fresh weight (i.e., fruit yield) was highly correlated with fruit dry weight. Aboveground dry matter production was correlated with both light use efficiency and intercepted photosynthetically active radiation. Although the number of fruits was correlated with the fruit set ratio, no correlation was found between the number of fruit and fraction of dry matter distributed to fruit. The correlation between the fraction of dry matter partitioned to fruit and fruit dry weight varied by plant stage, potentially due to the yield fluctuation called “flush”. Together, these findings suggest that to improve the yield of sweet peppers in Japan, we should focus first on improving light use efficiency.
The effects of End-of-Day (EOD)-cooling on floral differentiation and cut flower characteristics in carnation were verified using both short-term model-based experiments in a growth chamber and long-term demonstrative experiments in a greenhouse. In the model experiment, flower buds were undifferentiated until 43 days after pinching in both control and End-of-Night-cooled plants. In contrast, in the EOD-cooling treatment, every set reached the reproductive phase by 22 days after treatment. At the same node position, a three-stage advancement in floral differentiation was observed after EOD-cooling, but not after the other two treatments. This suggested that EOD-cooling promoted both floral differentiation and development in carnation. For the demonstrative experiment, significant differences between EOD-cooled and control plants varied each year in days to flowering, node order of flowering, and stem weeping angle. Because environmental factors could affect variation, correlations between the diurnal temperature range and the difference in each survey component were examined using regression analyses. Moderate (days to flowering) and a strong (node order of flowering) correlations were found with the diurnal temperature range. Thus, the EOD-cooling treatment was advantageous in suppressing delayed flowering over a large diurnal temperature range during floral differentiation. The difference in stem weeping angle showed a strong correlation with the difference in minimum temperature during the stem elongation stage. Improving the stem quality by EOD-cooling tended to be effective under high minimum-temperature conditions.
Japanese cucumbers are unique in terms of their production methods, such as steamed cultivation in which the greenhouse is closed to increase the temperature and humidity. Moreover, Japan has strict standards for fruit size. Therefore, most research on greenhouse cucumbers in Japan has focused on pests, diseases and fruit quality, and few studies have focused on increasing yields. Therefore, we aimed to contribute to a yield improvement in Japanese greenhouse cucumber production by considering environmental factors and training methods based on the yield components. Here, we discuss different training systems, pinching and lowering methods, and the effects of environmental factors such as temperature, humidity, CO2 concentration, irrigation, and nutrition on yield and yield components. Moreover, this paper also proposes future areas of research for Japanese greenhouse cucumbers.
We used instruments to analyze the texture of compressed samples obtained from the equatorial portion of apples cut in radial and tangential directions. The flesh firmness evaluation of apples using a penetrometer (Magness-Taylor type) showed a year-to-year correlation, and this was highly correlated with mechanical values, including maximum force (N) evaluated using two instruments in both the radial and tangential directions. On the other hand, no significant relationship between the mechanical values obtained from the instruments and the sensory test results of flesh texture was observed. We adopted a crispness index (CI) value to characterize the mechanical response during the penetration test. The CI value was not correlated with most of the mechanical parameters in the Rheoner analysis. Additionally, we used a TA.XTplus texture analyzer to obtain mechanical and acoustic responses during the penetration test. The maximum and average acoustic pressures (dB) were not correlated with the mechanical parameters. There was a significant correlation between the acoustic profiles and the CI values obtained from the instruments. These results revealed that the CI and acoustic profiles were physical responses that differed from mechanical ones when measuring the flesh texture of apple fruit. In this study, the CI and acoustic pressure were associated with the sensory test results of flesh texture, suggesting that these parameters were effective for objectively evaluating the flesh texture of apples. The cultivars and selections evaluated as having high crunchiness by sensory test showed relatively high CI values and acoustic pressure. In addition, the CI value showed a significant year-to-year correlation (r = 0.68**), implying that it was one of the genetic characteristics responsible for the flesh texture of apples.
An in vivo micrografting method was developed to obtain Passiflora latent virus (PLV)-free passion fruit from infected plants. The scion length required to eliminate PLV was ≤ 2 mm. The method required no aseptic handling and the procedure was relatively simple, and resulted in more than 10 micrografts in one hour. Moreover, no special equipment or procedures were necessary, allowing it to be conducted at an individual farm level. Rapid growth of the scion after grafting was also observed due to the use of fully established seedlings as rootstock. Leaf samples for analysis of PLV infection could therefore be obtained about two months after grafting with fruit harvest possible about four months later. In vivo micrografting was conducted with a scion length of 0.5–1 mm from September to November to determine the optimal air temperature conditions. The graft success rate increased from 18% to 58% with a decrease in the average air temperature from September (28.6°C) to November (23.3°C), although there was no significant difference in PLV-free rates between months (73% to 80%). Accordingly, in vivo micrografting of passion fruit is not recommended under high air temperature conditions. The effect of scion shoot storage conditions was also examined, revealing that in vivo micrografting using shoots stored for one day could be performed without difficulty, whereas the rate of graft success and PLV-free rate were close to those obtained using shoots selected less than 30 min before. These findings suggest that with this method, virus-free plants can be obtained using PLV-infected shoots selected in the field one day earlier. In conclusion, our in vivo micrografting technique is useful to eliminate PLV from infected plants; it is simple and leads to rapid growth of the scion after grafting.
To prevent the decay of satsuma mandarin fruit during the distribution process, we investigated the effect of ultraviolet-C (UV-C) irradiation and temperature treatment (TT) on scoparone (a phytoalexin) production in fruits. To this end, the fruits were maintained at 20°C for 24 h following irradiation, and then the scoparone content was measured after export to Singapore by sea freight or after domestic storage. The scoparone content in the flavedo of TT fruits significantly increased for 24 h after UV-C irradiation, compared with that in the flavedo of non-TT fruits. In fruits exported in reefer containers (0°C), the scoparone content in the TT fruits was 59.1 μg·g−1FW, whereas that in non-TT fruits was 15.1 μg·g−1FW. The domestically stored fruits showed similar trends to those of the exported fruits. The scoparone content in domestically stored fruits was higher than that in the exported fruits because the storage temperature was higher than the temperature in the reefer container used for export. There was a significant difference in the decay rate between UV-C-irradiated and non-irradiated fruits. These results showed that UV-C irradiation was effective in reducing the decay of fruits exported by sea, and TT before storage induced scoparone production in the flavedo, even under cold storage.
Brassica napus L. is an important oil crop in China. Most of the oil from B. napus is stored in oil bodies. In this study, the biogenesis of oil bodies and variations in the gene expression levels of oil body proteins and fatty acid synthesis transcription factors were characterized during embryogenesis using ultrastructural observations and quantitative polymerase chain reaction. When comparing the fluorescence intensities of Nile red staining in embryos at various stages, increasing numbers of oil bodies were observed in B. napus embryos after the globular embryo stage. Oil bodies were observed in early embryos in the embryo itself and in suspensors at 9–11 days after pollination (globular embryo stage) using ultrastructural analyses. There were more oil bodies in embryos at the torpedo-shaped embryo stage than at the heart-shaped embryo stage. In addition, the gene expression levels of oil body proteins, including oleosins, steroleosins, and BnCLO1, but not BnCLO3, increased during the heart-shaped embryo stage and these elevated levels were maintained during the subsequent developmental stages. The expression levels of fatty acid synthesis transcription factors (BnLEC1, BnL1L, BnWRI1, and BnFUS3) increased during the early stages and decreased during the later stages, while their peak expression times differed. Expression of BnLEC1 was the first to peak, followed by BnL1L, BnWRI1, and BnFUS3. We characterized oil body formation during the early embryonic development of B. napus, including the first examination of oil bodies in globular embryos. We also documented numerical variation in oil bodies during early embryogenesis, which was consistent with the gene expression levels of oil body proteins and fatty acid synthesis transcription factors.
The growth and yield of tomatoes in greenhouses covered by heat insulation film were investigated in Ishigaki, a subtropical area of Japan with high temperature and high solar radiation. High-density planting of tomatoes was carried out in June, July, August, October, and November, with a low node-order pinching system. The plants were grown in two greenhouses, one covered by a thermal barrier film (TBF) for heat insulation and the other covered by a polyolefin film (PO). Under TBF, the maximum temperature was up to 3.6°C lower than that under PO, and the mean temperature was 0.4°C lower. The leaf area index (LAI) of the June planting was 3.0 under TBF and 3.4 under PO, significantly lower than the LAIs of the other plantings, which ranged from 3.9 to 5.4. The specific leaf area (SLA) varied with the cultivation season, with that under TBF and PO being highest in November plantings grown in winter. SLA under TBF was higher than that under PO in the same cultivation seasons. The amount of total aboveground dry matter was significantly lower in the June planting under TBF and showed no difference in other plantings. Distribution to fruit was higher under TBF than under PO, especially in summer cultivation. The yields under TBF were significantly higher than those under PO in the July planting, and the yields under PO were significantly higher in the November planting. Under TBF, the rate of fruit cracking was reduced in the June, July, and August plantings. Under TBF and PO, plantings in October and November produced puffy fruits. The light use efficiency under TBF was higher than that under PO in the same cultivation seasons, apart from the June planting. Tomato cultivation under TBF reduced the damage from intense solar radiation during summer. TBF enabled penetration of sufficient solar radiation to distribute photosynthates to each part of the plant because of a limited sink and abundant solar radiation in a subtropical summer. These results indicate that TBF and sink-limited cultivation are effective systems for use in the high temperature and high solar radiation environments of tropical and subtropical regions.
The tomato leaf curl New Delhi virus (ToLCNDV) is a bipartite begomovirus (genus Begomovirus, family Geminiviridae) that was originally isolated in India, but has become a serious threat to various horticultural crops in the Indian subcontinent, Southeast Asia, East Asia, Middle East, and western Mediterranean Basin. In Southeast Asia, East Asia, and the western Mediterranean Basin, ToLCNDV has caused huge economic damage to cucurbit crops (cucumber, melon, squash, and zucchini) for which commercial ToLCNDV-resistant cultivars are currently unavailable. In this study, full-length ToLCNDV viral sequences were isolated from cucumber, melon, and zucchini plants exhibiting yellow leaf curl disease in Almeria, Spain. Phylogenetic analysis showed that the isolated viruses consisted of the ToLCNDV-ES strain and strains that were genetically distant from ToLCNDV-[BACu-20] in Southeast Asia, which were previously isolated in the Aceh province of Indonesia. Infectious clones of ToLCNDV-[ES-Alm-Cuc-16] from Spain and of ToLCNDV-[BACu-20] from Indonesia were prepared, and ToLCNDV isolates were agroinoculated to Nicotiana benthamiana, tomato, and cucurbit crops (cucumber, melon, and zucchini). Infection rates were nearly 100% for all inoculated plant species, and disease symptoms were consistently more severe in plants inoculated with ToLCNDV-[BACu-20] compared to plants inoculated with ToLCNDV-[ES-Alm-Cuc-16]. For tomatoes inoculated with ToLCNDV-[ES-Alm-Cuc-16], infection occurred without symptoms in most plants, and only a few plants showed slight vein-yellowing symptoms. In contrast, ToLCNDV-[BACu-20] infection induced typical begomoviral disease symptoms of yellowing and curling of leaves in the same tomato cultivar. The present study highlights the importance of screening genetic resources for ToLCNDV resistance by using ToLCNDV isolates from the intended production area; furthermore, the agroinoculation method used in this study will facilitate breeding resistance against both the Southeast Asian and Mediterranean ToLCNDV isolates.
Bulb onion (Allium cepa L.) contains several functional components such as quercetin glycosides, a type of flavonoid. The quercetin content of bulb onion has been determined at harvest and storage; however, little is known about the changes in quercetin accumulation during development. In this study, two yellow onion varieties, ‘Momiji No. 3’ and ‘Quergold’, which differ in quercetin content at harvest, were grown on lowland soil following spring sowing in 2018 and 2019. Then, the changes in quercetin accumulation and composition in the bulbs and leaf blades from the seedling stage to harvest were evaluated. In both years, quercetin accumulation in the bulbs followed a similar trend, with ‘Quergold’ tending to have a higher quercetin content than ‘Momiji No. 3’, except for two weeks following transplanting. Significant differences between the quercetin contents in the two varieties were observed at harvest. The content of quercetin-4'-glucoside (Q-4'-G) was the same or higher than that of quercetin-3,4'-diglucoside (Q-34'-DG) throughout development, except on October 6, 2018, and July 29, 2019, in both varieties. Meanwhile, the quercetin content per bulb increased with bulb formation in both varieties. In contrast, quercetin accumulation in the leaf blades was lower than that in the bulbs throughout development in both years. An increase was observed from July, with accumulation of Q-34'-DG dominating until early July, whereafter accumulation of both Q-34'-DG and Q-4'-G was observed until harvest. Overall, these findings suggest that accumulation of quercetin glucoside content varies dramatically with growth, differing between onion bulbs and leaf blades.
In this study, we examined sucrose metabolism and expression of invertase, a sucrolytic enzyme, during vegetative and floral development in Eustoma grandiflorum, a widely cultivated ornamental plant. During vegetative growth, sucrose content was relatively lower in roots and unexpanded leaves than in expanded leaves. The activities of cell-wall invertase (CWIN) and vacuolar invertase (VIN) were higher in roots and unexpanded leaves, respectively, whereas the activity of cytoplasmic invertase (CIN) was higher in both organs. During flower development, although the contents of reducing sugars and sucrose were relatively unchanged, starch content was higher in elongated flower buds (stage 2), and we also detected a significant increase in CWIN activity. VIN and CIN showed contrasting changes in enzymatic activity, with the former being higher, and the latter lower in opened flowers (stage 3). Furthermore, we cloned two putative CWIN genes (EgCWIN1 and EgCWIN2), one putative VIN gene (EgVIN1), and one putative CIN gene (EgCIN1), and examined the transcript levels of these four genes. Although we detected no clear correlations between invertase activities and the transcript levels of invertase genes in vegetative organs, we observed changes in the transcript levels of EgCWIN1, EgVIN1, and EgCIN1 corresponding to changes in activities of the respective invertase during flower development. These results indicate that carbon partitioning during vegetative and floral development in E. grandiflorum is controlled by three invertase isoforms, and that differential gene expression underlies the successive induction of these invertase isoforms during flower opening.
Many cut flowers are treated with an ethylene action inhibitor, silver thiosulfate (STS), to delay senescence and are shipped by dry transport that involves relatively easy loading. In addition, cut flowers are often treated with a mixture of sugar and germicide to improve their vase lives. Exogenous treatments of these compounds or drying by transport are thought to have various effects on cut flowers. This study investigated the effects of these post-harvest management methods on the scent emission of carnation (Dianthus caryophyllus L.) cut flowers. Under all the management conditions, the total scent emissions of cut flowers were highest on harvest days and then decreased, but major changes in their compositions were not observed. The decreases in scent emissions were thought to occur earlier than the known ethylene induction in carnation cut flowers, which is equivalent to the 4th day after harvest. The STS treatment had no effect on the scent emissions for some time after harvest, but suppressed the decreases in scent emission 4–8 days after harvest under the wet transport condition. It is likely that the decreases in scent emissions in carnation cut flowers occur in an ethylene-independent manner, but ethylene induction a few days after harvest further promotes decreases under wet transport conditions. STS may have suppressed the promotion of decreases due to ethylene. On the other hand, the treatment that assumed dry transport for one day dramatically promoted the decreases in scent emissions. Since the promoting effects were not affected by the STS treatment, they were considered to be ethylene-independent. A common sugar treatment with 1% glucose, sucrose, or fructose did not affect the scent emissions in the cut flowers. An isothiazolinonic germicide, which is a common cut flower germicide, did not affect the treatment. Considering the current post-harvest process, the duration of a noticeable scent in carnation cut flowers can be expected to be extended by adopting wet transport instead of dry transport.