To improve labor-saving during harvests, the efficiency of handpicking fruit was examined for the satsuma mandarin with the plant growth regulators gibberellin (GA), prohydrojasmon (PDJ), and ethephon (ET). In this study, concentrations of plant growth regulators were set 5 mg·L⁻¹ for GA and 50 mg·L⁻¹ for PDJ, respectively. Spraying of a GA plus PDJ solution on Aug. 27, Sep. 21, and Oct. 27 (triplicate spraying) improved the success rate of handpicking (SRH), as compared with a control. Furthermore, ET treatment in addition to triplicate spraying of GA plus PDJ increased SRH. A one-time treatment of GA plus PDJ also showed a significant effect on handpicking efficiency when applied in mid to late September. It was clear that the effect of GA plus PDJ on SRH was improved when 400 mg·L⁻¹ ET was used instead of 200 mg·L⁻¹, but this ET concentration (400 mg·L⁻¹) caused massive leaf abscission (data not available). Spraying with 300 mg·L⁻¹ ET alone showed 37.1% leaf abscission: therefore, we assumed that a GA plus PDJ treatment with a combination of less than 300 mg·L⁻¹ ET would increase peel firmness without serious leaf abscission and a negative effect on SRH. In addition, the soluble solids and the acidity in the combination spraying of GA plus PDJ in late September with 300 mg·L⁻¹ ET and less were almost the same as the control. Thus, our results indicated that the treatment of 5 mg·L⁻¹ GA plus 50 mg·L⁻¹ PDJ in late September combined with ET (200 mg·L⁻¹ < ET < 300 mg·L⁻¹) from late October to early November was suitable for increasing SRH without impairing fruit quality and causing serious leaf abscission.

In common apple cultivars with white flesh and red skin, it is known that fruit overload lowers fruit quality, and that skin anthocyanin concentrations are reduced by bagging treatment and warmer climatic conditions. In this study, the effects of these factors on anthocyanin accumulation in the flesh of red-fleshed apples were investigated using ‘Geneva’ and ‘Pink Pearl’ apple cultivars. Excess fruiting resulted in decreased anthocyanin concentration in the flesh and the titration acidity of the fruit in both cultivars. Fruit bagging treatments using double-layer paper bags revealed that anthocyanin was synthesized to a certain extent in the flesh under dark conditions in both cultivars. The treatment significantly reduced anthocyanin accumulation in the flesh of bagged ‘Geneva’ apples compared with unbagged fruit, but no inhibitory effect was clear in ‘Pink Pearl’ apples. In both cultivars, the anthocyanin concentration in the flesh of unbagged apples grown in sunlight was higher than that in unbagged apples grown in shade, whereas there was no difference between positions for bagged fruit. In apples grown in either sunlight or shade, no significant difference was found between anthocyanin concentrations in the sun-exposed side and shaded side of fruits. These results indicate that sunlight irradiation partially promoted anthocyanin accumulation in the flesh of unbagged ‘Geneva’ and ‘Pink Pearl’ apples and accelerated its accumulation on both the sun-exposed and the shaded side. A comparison of the fruit quality of ‘Pink Pearl’ apples grown in different climatic regions showed that apples harvested at Suzaka, a warmer region, were lower in firmness, starch index, and titration acidity and higher in soluble solids concentration compared with those from Morioka, a cooler region. The anthocyanin concentration in the flesh of ‘Pink Pearl’ apples from the trees grown at Morioka was more than ten-fold higher than that in apples from the trees grown at Suzaka. Our results suggest that an appropriate fruit load, growth in sunlight, and growth under cooler climatic conditions, may redden the flesh of red-fleshed apples, as is the case for common apples.

Pruning is a recommended cultural practice in blueberries (Vaccinium spp.) to maintain the balance between vegetative growth and reproductive development. Winter pruning is common and well-documented practice. Summer pruning, however, has been less studied. In this study, 5 primaryshoots (PSs) were selected per treatment (pruning date) on 5 different bushes (replications) of the rabbiteye blueberry (Vaccinium virgatum Ait.) ‘Tifblue’ and half-length headed back during its active growth period from June through Nov. The hypothesis tested in this study was that summer pruning induces flower buds at the basal area of PSs, controls the plant canopy and makes it possible to harvest fruits in the next summer season from the same shoots. In this study, there were no significant differences observed among any treatments with respect to yield and fruit quality. Early summer pruning (June) stimulated secondaryshoots (SSs) and later in autumn, terminal flower buds of these SSs produced fruits in the following year. However, no SSs were produced after summer pruning in Sept., and only vegetative buds that were at the basal area of PSs differentiated to flower buds and produced fruits in the following year. In conclusion, summer pruning can be practiced to complement or replace winter pruning and growers could decide the date of summer pruning in accordance with the size of plants’ canopies. Plants with smaller canopies can be pruned in June and those with bigger canopies can be pruned in Sept.

In citrus trees, a technique for predicting the number of flowers is needed to prevent inconsistent fruit production over time. In this study, we investigated whether a flowering-related gene, citrus FLOWERING LOCUS T (CiFT), can be used to predict floral production. We quantified CiFT expression levels in stems of Satsuma mandarin (Citrus unshiu Marc.) trees planted at two remote locations. We collected samples over 3 years, and determined that the CiFT mRNA levels in November were strongly correlated with the number of flowers produced the following spring. The correlation between CiFT expression and floral production exhibited almost no differences among years or between sample collection sites. Thus, the CiFT expression level in November can be used to predict the number of flowers the following spring, and this prediction method can be used at different locations and over several years. To verify the practical utility of this method, Satsuma mandarin shoots were transported in November from eight locations across Japan to our laboratory under cool conditions. Transport times were approximately 4–72 h, and samples were immediately frozen upon arrival. The CiFT expression levels in transported stems correlated with the number of flowers in the following spring. Additionally, those correlations were similar in transported samples and samples that were frozen immediately after collection. Our results suggest that the number of flowers can be predicted even with the CiFT expression levels quantified in transported samples.

With the continuing trend of global warming, the adverse impact of high temperature and the inevitably accompanying drought stress on the growth of Japanese apricot trees (Prunus mume Siebold et Zucc.) are of concern. Therefore, the effects of these factors on photosynthesis and carbohydrate translocation were analyzed. An investigation was conducted at average daytime temperatures of 24°C, 30°C, and 34°C under both irrigated and drought conditions. The 34°C temperature was higher than the open air temperature by 5°C. Stable isotope ¹³C was administered to trees to determine carbohydrate positioning. Under the drought stress condition, the photosynthetic rate declined accompanied by temperature elevation, and at the highest temperature of 34°C, ¹³C concentrations in the twigs and roots were lower than those in the irrigated trees at 24°C. Two-way analysis of variance revealed a trend of ¹³C translocation to the young organs above ground, and old organs, while roots were affected by water status, temperature, and their combination, respectively. In the irrigated trees, the photosynthetic rate reduction was not detected, even at higher temperatures. However, translocation incompetence reflecting a decline in ¹³C concentration in the roots was observed at 34°C. These results indicate that the permissible diurnal average temperature during summer for the growth of Japanese apricot trees is approximately up to 30°C, and in the temperature range around this irrigation is helpful to facilitate regular functioning of carbohydrate translocation under drought stress conditions.

Fluridone, an inhibitor of carotenoid biosynthesis, is known to prevent abscisic acid (ABA) biosynthesis and to affect the germination and dormancy of seeds in several plant species. This study investigated the effects of fluridone on seed germination of the ornamental peach ‘Yaguchi’, and on the transcript levels of genes related to seed dormancy in this plant. Seeds were rinsed for 2 days under running tap water (RS), then soaked for 1 day in 100 μM fluridone (F), and kept at 5°C for 2 weeks (2W). The germination rate significantly increased from 0% to 9.5% in the RS+F treatment and to 71.4% in the RS+F+2W treatment, while no germination occurred in the RS and RS+2W treatments. Seedlings in RS+F and RS+F+2W treatments formed dwarf shoots, i.e. about 10 cm, and morphological lesions on the leaves. The ABA content in embryonic axes decreased after RS and increased with RS+2W. It was decreased by the RS+F+2W treatment. RS+F+2W downregulated ABA-hy3, which encodes enzymes with key roles in ABA catabolism, while its effects on 9-cis-epoxycarotenoid dioxygenase (NCED1) in relation to ABA synthesis fluctuated. In contrast, Empfindlicherim Dunkelroten Licht 1 (EID1) was upregulated after fluridone treatment, suggesting that fluridone may activate positive ABA signaling pathways. Expression of GA2-oxidase8 (GA2-ox8) was not affected by fluridone. MADS-box protein JOINTLESS (LeMADS) and Late embryogenesis abundant protein D-34 (LEA D-34) were downregulated in the RS+F+2W treatment, suggesting that the expression of these genes are controlled by low temperature and the ABA inhibitor, and are involved in seed dormancy. These results suggest that ABA inhibitor treatments can be an alternative method to promote germination by controlling ABA content and its metabolism, and consequently changing expression of certain ABA- and dormancy-related genes including ABA-hy3, EID1, LeMADS, and LEA D-34, even under insufficient chilling conditions.

Calcium (Ca²⁺) concentration, early fruit growth, and expression of Ca²⁺-movement-related genes were analyzed during early fruit development in the tomato, which is the most important stage regarding the incidence of blossom-end rot (BER), to investigate the physiological mechanisms affecting the occurrence of BER. We used tomato introgression line IL8-3 with a chromosome segment from a wild relative (Solanum pennellii) because this line shows lower incidence of BER compared with the parent cultivar ‘M82’ (S. lycopersicum), as described previously. Ca²⁺ concentration in fruit and leaves was higher in IL8-3 than in ‘M82’, whereas no significant differences were observed between Ca²⁺ concentration in roots and stems of ‘M82’ and IL8-3. These results suggested that a Ca²⁺ transport property is an essential factor for the lower incidence of BER in IL8-3. IL8-3 fruit showed a lower growth rate than ‘M82’, which could result in preventing the occurrence of BER. The expression of genes encoding cation exchangers, Ca²⁺-ATPases, a Ca²⁺ channel, and Na⁺/Ca²⁺ exchangers, was higher in IL8-3 fruit than in ‘M82’ fruit, suggesting active Ca²⁺ movement in IL8-3. All results in this study could be related to physiological mechanisms accounting for the lower incidence of BER in IL8-3.

Hardening with a high vapor-pressure-deficit (VPD) can decrease conductance (g_s) and thereby enhance drought tolerance by reducing transpiration, which is particularly useful during transplant establishment. However, high-VPD hardening may decrease photosynthetic performance due to stomatal (diffusion) and non-stomatal (mesophyll) limitation. If g_s can be lowered without significantly reducing photosynthesis, water-use efficiency (WUE = CO₂ assimilation/transpiration), which is an important criterion for transplant quality, would improve. We investigated the photosynthetic properties of cucumber (Cucumis sativus L.) leaves acclimatized to different VPD levels (0.4 and 3.2 kPa at 28°C), and determined whether photosynthesis was limited by stomatal or non-stomatal factors at high VPD. The net photosynthetic rate (P_n) and g_s were measured at a VPD of 0.8 kPa and a leaf temperature of 28°C under saturating light. The photosynthetic response to the intercellular CO₂ concentration (C_i) was used to quantify the effects of VPD acclimatization on carboxylation efficiency. P_n did not differ significantly between acclimatization VPDs, but g_s was much lower (×0.36) in high-VPD leaves at an ambient CO₂ concentration of 400 μmol·mol⁻¹. Thus, the intrinsic WUE (= P_n/g_s) of the high-VPD leaves was much higher (×2.85). The C_i of high-VPD seedlings was lower than that of low-VPD seedlings, but, this did not cause any significant reduction in P_n in the high-VPD treatments because the decrease in C_i occurred within a range in which photosynthesis was not limited by ribulose-1,5-bisphosphate carboxylation in this experiment. The P_n–C_i curve did not differ between the VPD treatments, indicating that carboxylation efficiency was not affected. When VPD-acclimatized seedlings experienced a limited water supply, the low-VPD leaves showed lower leaf water potential and more severe wilting than the high-VPD leaves 30 min after water limitation began. The g_s of the high-VPD leaves was significantly lower (approximately ×0.5 in average) than that of the low-VPD leaves throughout the water-supply-limitation treatment. The lower g_s maintained the water status of the high-VPD leaves at less-wilting levels by decreasing transpiration. These results indicate that high-VPD hardening could enhance the tolerance to short-term drought without stomatal or non-stomatal limitation of photosynthesis when controlling g_s effectively.

Lettuce (Lactuca sativa L.) bolting is often limiting in agricultural production as stem elongation followed by flower bud differentiation results in unmarketable plants. Thus, to solve this problem, it is important to elucidate the molecular mechanisms controlling flowering. To investigate the relationship between gene expression and flowering in lettuce, homologs of flowering-related genes were isolated and their expression over time was analyzed in three cultivars and in one breeding line by using quantitative real-time PCR. In plants grown in the field, the expression of the lettuce homologues APETALA 1 (LsAP1L) and LEAFY (LsLFYL) in the shoot apex correlated with flower bud formation, and FLOWERING LOCUS T (LsFT) expression increased during the transition from vegetative to reproductive growth. The transcription of FLOWERING LOCUS D (LsFLDL), FVE (LsFVEL), and LUMINIDEPENDENS (LsLDL) also increased with flowering. Our previous study showed that LsFT was upregulated during lettuce flowering induced under controlled high temperature conditions. Results from both studies suggest that LsFT is involved in lettuce flowering, both in natural and controlled conditions. This is also the first report on the expression of other flowering-related genes along with flowering of lettuce grown in the field.

Although ultraviolet-B (UV-B) light (280–315 nm) irradiation effectively controls spider mites in horticultural crop production, it also causes plant damage, leading to growth suppression, changes in morphology, and leaf scorching. However, sensitivity to UV-B varies among plant species. Here, we assessed the effect of UV-B on growing perilla (Perilla frutescens var. crispa) plants. Three experiments were conducted. In the first experiment, plants of the variety ‘Akachirimenshiso’ were grown in a plastic house with natural light conditions and subjected to three treatments: natural UV (control), −UV, and natural UV plus artificial UV-B treatment (50 mW·m⁻²) from 0:00 to 3:00. The length of leaf blades that received additional UV-B treatment was reduced by 16.5% and 32.3% in two trials compared with that of the respective controls. In this experiment, additional UV-B irradiation turned the leaf color greener. During UV-B treatment, the values of leaf a*, an indicator of leaf redness, were significantly lower than their respective controls in both trials: 21.5 vs. 31.6 in trial I and 20.2 vs. 30.7 in trial II. For most of the parameters measured in this experiment, no differences were observed between the control and −UV treatment groups. In the second experiment, plants were irradiated with UV-B for 3 weeks at nighttime (0:00–3:00) or daytime (12:00–15:00). In the cultivar ‘Houkouakashiso’, the length of leaf blades significantly decreased by 15.9% and 20.6% under nighttime UV-B irradiation at 80 and 120 mW·m⁻², respectively, compared with that of the non-irradiated controls. Irradiation at 80 mW·m⁻² also decreased the width of the leaf blades by 13.1% and that at 120 mW·m⁻² further decreased it by 25.0%. These results showed that UV-B irradiation at night decreased the size of perilla leaves. In addition, the value of a* became lower under UV-B irradiation in the nighttime. Thus, UV-B irradiation appeared to turn purple perilla leaves green. When plants were irradiated with UV-B in the daytime, there was no significant difference between irradiated and non-irradiated plants in the length or width of leaf blades, a*, or fresh weight of aerial parts and number of nodes on the main stem. In the third experiment, visible rays (VIS) emitted by fluorescent lamps were applied at 0:00–3:00 and 6:00–22:00. Plants were irradiated with 120 mW·m⁻² of UV-B at 0:00–3:00. UV-B + VIS treatment of ‘Akachirimenshiso’ with VIS from fluorescent lamps did not significantly affect the parameters measured in this experiment compared to −UV treatment. The results of this study suggest that UV-B damage to perilla leaves can be avoided by combined irradiation with visible light.

Tomato plants were grown with a drip irrigation system to evaluate the effects of a novel organo-mineral fertilizer [2:10:1 (w/w/w) mixture of calcium sulphate, ground rice bran, and humic acid] (OMF), which can mitigate salinity stress, on plant growth, fruit yield, and the incidence of blossom-end rot (BER) under salinity stress. Salinity stress was applied by drip irrigation with 50 mM of NaCl. Plant growth with OMF was lower than that with chemical fertilizer (CF). Higher levels of K and P were obtained in the leaves from plants grown with OMF. OMF inhibited Na accumulation and proline increase in the leaves and was considered to alleviate salinity stress. Salinity treatment caused a decrease in fruit weight and an increase in ascorbic acid, sucrose, glucose, fructose, and glutamic acid. Tomato plants grown with OMF had smaller fruit than with CF without salinity, but the incidence of BER under salinity was reduced by OMF. The water soluble Ca content of the distal half of young tomato fruit was significantly decreased with salinity treatment. The incidence of BER under salinity was significantly lower in OMF than in CF, but there was no difference in the concentration of every form of Ca between CF-salinity and OMF-salinity treatments. The reduction in BER incidence with OMF treatment could not be explained by the differences in Ca concentration. The mechanism of the reduction in BER with OMF was not clear, so further studies are necessary.

A strawberry core collection was established based on simple sequence repeat and cleavage amplified polymorphic sequence marker polymorphisms in 119 strawberry cultivars using the “PowerCore” program. The core collection consisted of 19 cultivars. The correlation coefficients for the diversity index were significant between the core collection cultivars and all cultivars. Allele frequencies of each marker allele were not significantly different between the core collection cultivars and all cultivars according to Fisher’s exact test. Cluster analysis indicated that the selected core collection cultivars evenly distributed throughout the multiple clusters and principle component analysis clearly showed major principle components of core collection cultivars distributed widely among those of all cultivars. Furthermore, core collection cultivars tended to harbor minor alleles. These results demonstrated that the core collection cultivars were suitably selected in terms of reflecting the genetic diversity of all strawberry cultivars.

Lilium auratum var. auratum Lindl. is distributed in the eastern part of Honshu, the main island of Japan. L. auratum var. platyphyllum Baker is endemic to the Izu archipelago, which consists of nine large islands located in south of Honshu’s Izu peninsula. Both varieties have been used as important parents of Oriental hybrid lily cultivars. They have large white flowers with yellow central stripes and colored spots on their tepals. L. auratum var. platyphyllum has larger flowers and wider leaves than L. auratum var. auratum. L. auratum var. platyphyllum has yellow spots, whereas L. auratum var. auratum has red or brown ones. Natural hybridization between these two taxa has been suggested on the basis of spot colors of populations in the Izu archipelago and the Izu peninsula. However, their genetic diversity and hybridity in nature have not been reported. We performed morphological analysis using 72 individuals of L. auratum var. auratum from seven populations and 72 individuals of L. auratum var. platyphyllum from six populations. We also performed simple sequence repeat (SSR) analysis using 102 individuals of L. auratum var. auratum from seven populations and 134 individuals of L. auratum var. platyphyllum from six populations. Both analyses revealed that L. auratum var. auratum and L. auratum var. platyphyllum are genetically different and that L. auratum var. platyphyllum has genetic diversity among populations in the archipelago.

To increase the photosynthesis of crop and improve plant quality, we evaluated the effect of elevated CO₂ on vegetative growth and flowering in Phalaenopsis ‘Fuller’s Pink Swallow’. Plants were exposed to 450 (control), 800, 1600, and 2400 μmol·mol⁻¹ CO₂ for 31 weeks. The number of leaves, leaf length, and leaf width displayed greater increases in plants grown under 1600 and 2400 μmol·mol⁻¹ CO₂ than in plants grown under 450 and 800 μmol·mol⁻¹ CO₂. The times to leaf initiation were reduced to 90.7 and 85.8 days in plants grown under 1600 and 2400 μmol·mol⁻¹ CO₂, respectively, compared with that of the control, 177.1 days. The leaf elongation rate was significantly increased in plants grown under 1600 and 2400 μmol·mol⁻¹ CO₂ compared to plants grown under 450 and 800 μmol·mol⁻¹ CO₂. Plants grown under 1600 μmol·mol⁻¹ CO₂ had the highest total number of flower buds among all plants grown under the four tested CO₂ concentrations. Leaf injuries were not observed in any plants regardless of CO₂ concentration, but flower bud abortion and bud withering were observed in CO₂-enriched plants, especially in plants grown under 1600 and 2400 μmol·mol⁻¹ CO₂. Plants subjected to long-term CO₂ elevation of over 800 μmol·mol⁻¹ displayed increased biomass production despite a concomitant reduction in the number of buds. These results showed that 1600 and 2400 μmol·mol⁻¹ CO₂ significantly enhanced the vegetative growth of Phalaenopsis. However, long-term exposure to high CO₂ concentrations can adversely affect the flowering of Phalaenopsis, and result in reduced flower production and increased flower bud abortion.

Changes in light quality strongly affect several plant anatomical, physiological, morphological, and biochemical parameters of orchid tissue culture seedling growth. In this experiment, ways in which light quality influence plant photosynthesis, growth parameters, and carbon dioxide rhythms of different sizes (stage I, II, and III) of Phalaenopsis tissue culture seedlings were examined. Stage I (Seedlings of 1–2 cm in height with 1–2 leaves and 1–2 roots) tissue culture seedlings were grown under six different light qualities under a T5 fluorescent lamp: White, Red (610 nm), Red (658 nm), Blue (440 nm), Red (610 nm) + Blue (440 nm), and Red (658 nm) + Blue (440 nm). After 5 months, cultured seedlings exposed to the Blue (440 nm) treatment showed significantly higher responses in terms of leaf quantities and chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid content. On the other hand, seedlings subjected to the Red (658 nm) treatment grew more stems and presented with higher fresh weight and leaf lengths compared to the results of other treatments. The number of roots increased under the Red (658 nm), Blue (440 nm) + Red (610 nm), and Blue (440 nm) + Red (658 nm) treatments. Moreover, seedlings subjected to Red light (658 nm) showed significantly higher levels of Rubisco enzyme activity than those subjected to the other treatments. Phosphoenolpyruvate carboxylase activities recorded during the nighttime in seedlings subjected to Red light (658 nm) were also significantly greater. The results showed that during stage I, the concentration of carbon dioxide rhythm ranged from 1500–1800 ppm and reflected a C3 photosynthesis system. As the seedlings matured, the carbon dioxide rhythm decreased to 400–800 ppm at night and reached stage III (CAM plant). After 5 months of culturing, the carbon dioxide rhythm of the Red (658 nm) treatment seedlings changed from C3 to CAM, while seedlings subjected to the other treatments were still in the intermediate stage (stage II). From these results, we conclude that to enhance seedling growth through commercial production, Red (658 nm) should be applied.

The responses of three kiwifruit cultivars, Actinidia chinensis ‘Sanuki Gold’, A. chinensis ‘Rainbow Red’, and A. deliciosa ‘Hayward’ to various storage temperatures (0, 5, 10, 15, and 20°C) for 8 weeks were investigated. The rate of fruit which initiated ethylene production due to rot development increased with increases in storage temperature. Early-maturing cultivars, ‘Rainbow Red’ and ‘Sanuki Gold’ fruit stored at 5, 10, and 15°C showed drastic softening and a decrease in titratable acidity (TA) to an edible level within 4 weeks without detectable ethylene production, whereas fruit stored at 0 and 20°C maintained high firmness and TA even after 8 weeks unless they were infected with rot. A late-maturing cultivar, ‘Hayward’ fruit stored at 5 and 10°C softened more rapidly than when stored at 0, 15, or 20°C. Treatment with 1-Methylcyclopropene (1-MCP) did not suppress the low temperature modulated fruit ripening in any cultivars, indicating its independence from ethylene. These results suggest that ‘Sanuki Gold’ and ‘Rainbow Red’ are more sensitive to low temperatures compared to ‘Hayward’ and the sensitivity is involved in the determination of storage life and how early the fruit matures on the vine.