We applied the New Root-zone Environmental Control System (N.RECS), which comprises floor heating panels with chilled or heated water flow and heat-insulating pot trays, to cool the root zone of pot-grown strawberry (Fragaria × ananassa Duch.) nurseries in late summer, and investigated the effects on the subsequent flowering and yield in a super-forcing culture. Cooling at around 20°C with short-day (8-h daylength) treatment for 22 days accelerated and stabilized the flower bud formation of two June-bearing cultivars, ‘Nyoho’ and ‘Tochiotome’. The temperature at the soil surface, where the crown is located, was around 23°C on average during root-zone cooling, possibly acting as a cold stimulus on the shoot apical meristem, which initiated flowering. Root-zone cooling did not affect the development of new leaves during treatment. Combined root-zone cooling with short-day treatment promoted anthesis of the first inflorescence to the same degree as conventional night cooling, but neither did so alone. Weight-based early marketable yield before December was doubled but the total yield during October to March was not increased. These data suggest that root-zone cooling with short-day treatment of June-bearing strawberries may be applicable for super-forcing culture harvested from October to mid-November.
Many strawberry cultivars are developed in Japan each year; however, the characterization of each cultivar, including yield, is insufficient. As they may affect strawberry yield, leaf photosynthesis characteristics were determined for seven Japanese strawberry cultivars (‘Akihime’, ‘Benihoppe’, ‘Ibarakiss’, ‘Oi C berry’, ‘Sachinoka’, ‘Suzuakane’, and ‘Yotsuboshi’) and evaluated with reference to a C3 photosynthesis model. Plants were grown hydroponically with a substrate-filled elevated-bed system in a glass greenhouse. Leaf gas-exchange rates were assessed at different photosynthetic photon fluxes and CO2 partial pressures using full-expanded leaves of plants 130–150 days after transplanting (DAT). We found that the net photosynthetic rate (Pn) was higher in ‘Yotsuboshi’ and ‘Sachinoka’ than in other cultivars both under light-limited and light-saturated conditions. The difference in Pn was correlated with stomatal conductance (gs), irrespective of light conditions. We also measured leaf Pn under both CO2-limited and CO2-saturated conditions; however, there were only a slight differences in either capacity of ribulose-1,5-bisphosphate carboxylation or regeneration among cultivars. Our results suggest that a difference in gs contributed to variations in leaf Pn among Japanese strawberry cultivars.
Dwarf cherry tomatoes ‘Red Robin’ and ‘Tiny Tim Red’ were cultivated in two sections. The two sections were set as (1) section irradiated only by fluorescent lamps (main wavelengths 433, 543, and 610 nm; 230 μmol·m−2·s−1 of photosynthetic photon flux density) and non-treated with UV-A irradiation (hereafter, non-UVA), and (2) section irradiated with fluorescent lamps and treated with UV-A irradiation (maximum peak emission: 352 nm; 15.1 W·m−2 ultraviolet radiation intensity; hereafter, t-UVA). The fruit weight per plant and the number of fruits per plant were not significantly affected by cultivar or section. Regarding fruit quality, the fruit cracking rate was lower in the t-UVA than in non-UVA section. There were no anatomical or histochemical differences in fruit structure or distribution of pigments such as lycopene or β-carotene, but the shape of the pigment in the epidermal cells was needle-shaped in the non-UVA and unclearly-shaped in the t-UVA, so the pigment shape was different between the two sections. In addition, the number of layers of the hypodermis in the exocarp that accumulated the pigment was smaller in the t-UVA than in non-UVA section. Fruit components in t-UVA showed increased total soluble solids (TSS), titratable acidity (TA), and ascorbic acid content, but a decreased carotenoid content. Therefore, it was shown that UV-A irradiation had a positive effect on the TSS, TA and ascorbic acid content and had a negative effect on the size of the fruit per fruit and the carotenoid content. UV irradiation did not affect the yield per plant. Comparing ‘Red Robin’ and ‘Tiny Tim Red’, there was no significant difference in yield, but the fruit size of ‘Red Robin’ was larger, while and the fruit component of ‘Tiny Tim Red’ was higher than that of ‘Red Robin’. In conclusion, when cultivating tomato plants in a plant factory, further improvements in fruit size and composition are expected by appropriately adjusting the time and intensity of UV irradiation for each cultivar.
The flower seed industry is facing a variety of issues related to ongoing climate change. The closed plant production system (CPPS) may be a solution to these issues as the environment inside the system can be fully controlled to allow seed production from many plant species. In this study, the influence of an artificial light condition, one of the key factors influencing plant growth and development in CPPS, on gloxinia (Sinningia speciosa) seed production was investigated. Three types of lights: warm white (3200 K), daylight (6500 K), and red and blue lights (RB) at a photosynthetic photon flux density of either 150 or 200 μmol·m−2·s−1 were applied to gloxinia plants. The highest vegetative growth was found in plants grown under 3200 K at 200 μmol·m−2·s−1 light but this did not correlate with seed yield. Plants grown under RB light exhibited the most compact canopy. Day to anthesis, flower diameter and percentage of pod set were not significantly different among the light treatments. Gloxinia plants grown under RB light at 150 μmol·m−2·s−1 had the highest seed yield, which is attributed to higher pollen elongation and flower number. The effect of light quality on seed yield is strongly dependent on light intensity. Moreover, treatment with RB light resulted in longer pollen grains and seeds than the other light quality treatments. Gloxinia seeds from all light treatment exhibited more than 80% germination and similar seed vigor. The results from this study suggest that CPPS, with suitable light conditions, may be used for commercial gloxinia seed production.
Japanese apricot (Prunus mume) cultivars have been classified into several subpopulations, such as fruiting, fruiting-small, and ornamental, based on a variety of morphological traits and human preference. A recent genome-wide analysis indicated that these subpopulations show some genetic differentiation, but the fruit traits remain to be investigated. Therefore, we investigated phenotypic diversity of several fruit traits, such as sugar, organic acid, and volatile compound contents and compositions, in a variety of cultivars of Japanese apricot (P. mume), apricot (P. armeniaca) and their interspecific hybrids. We found that Japanese apricot cultivars show diverse phenotypic variation and that some fruit traits appeared to be associated with the differing subpopulations. The fruiting cultivars investigated appear to have higher contents of sugars and favorable volatile compounds such as lactones and esters. We also found that ‘Joshuhaku’, a local cultivar in Kyoto Prefecture, has desirable fruit traits including large fruit size, high contents of organic acid and favorable volatile compounds. Moreover, interspecific hybridization was found to have large effects on fruit traits. Our results indicated a wide diversity of fruit traits in Japanese apricot, in which sugars and volatile compounds were associated with fruiting cultivars. These observations may assist with the breeding of new Japanese apricot cultivars.
A combination of phytohormones and ethylene, a key regulator of sex determination, induces female flowers in cucumber plants. Several inhibitors of ethylene biosynthesis or action affect plant sex determination. However, the use of ethylene inhibitors to control sex determination in commercial cucumber production has not been reported. 1-Methylcyclopropene (1-MCP), a commercial ethylene antagonist that inhibits ethylene signaling, is used to maintain the freshness of many harvested horticultural products. In this study, we evaluated the effect of 1-MCP on the sex ratio in cucumber plants to reduce production of cucumber fruit by inducing male flowers and reducing labor time for harvest. A concentration-dependent induction of male flowers was observed. Dose-response curves were obtained from the male flower induction rate (MFIR) and the range of nodes producing male flowers induced by 1-MCP treatment. We applied these models in independent experiments to predict the number of nodes and emergence day of male flowers induced by 1-MCP treatment and confirmed that the prediction fitted the results. Based on these results, production of cucumber fruit could be controlled by 1-MCP treatment and temporary excess labor for harvest could be avoided by using this model.
Anthracnose, caused by the fungal pathogen Colletotrichum orbiculare, is one of the severest diseases in open-field cucumber (Cucumis sativus L.) cultivation in Japan. Genetically conferred host resistance is the best way to control anthracnose. In order to develop new cultivars resistant to anthracnose, identification of promising sources of resistance is vital. In this study, we screened 232 genetic resources of Asian origin preserved in the NARO Genebank and identified one accession, ‘Ban Kyuri’, with strong, although not perfect, resistance to anthracnose. Further evaluation of the resistance based on seedling and greenhouse assays confirmed resistance. We also revealed a wide variation in the virulence of three C. orbiculare strains in Japan. ‘Ban Kyuri’ exhibited stable resistance to all strains. Genotyping of CsSGR, a known gene for anthracnose resistance, indicated that ‘Ban Kyuri’ is homozygous for the wild-type allele, and its resistance level was equal to or higher than that of accessions harboring Cssgr, the mutated allele conferring resistance. This finding indicates that ‘Ban Kyuri’ harbors a novel resistance gene or a novel allele of CsSGR conferring anthracnose resistance. ‘Ban Kyuri’ is a promising new source of resistance to diverse anthracnose strains with different levels of virulence in Japan, and its use will help to further clarify the genetic mechanism of anthracnose resistance in cucumber.
Fasciation in strawberry is characterized by an enlarged and flattened receptacle, clustering of flowers, and altered inflorescence architecture. However, the developmental process of fasciated flowers remains obscure. In this study, the fasciation incidence and developmental process in the primary fruit and inflorescence architecture were evaluated and compared for the non-susceptible cultivars, ‘Nyoho’ and ‘Sagahonoka’ and one of the most susceptible cultivars, ‘Ai-Berry’. The severity and frequency of flower and inflorescence fasciation was clearly greater in the vigorously growing large plants of ‘Ai-Berry’ compared to small plants and large plants of the other two cultivars. In ‘Ai-Berry’, the deformation of the large shoot apical meristem (SAM) into an oval shape was the initial symptom observed before and during floral transition. Such oval-shaped SAMs often differentiated two or more leaf primordia almost at the same time, which then developed into divided multiple vegetative SAMs before floral transition and linearly-fasciated SAMs during floral transition, respectively. The development of fasciation symptoms was observed after downregulation of FaTFL1. Although inflorescence or receptacle fasciation could be controlled when early and rapid floral induction was achieved by intermittent low-temperature treatment, severe fasciation was observed in late-flowered plants which were either not responsive or not subjected to this treatment. These results indicate that fasciation of floral organs may be triggered and develop during floral transition and that temperature fluctuations around boundary values between floral inhibition to induction may cause a half-finished or slowly processed floral transition and finally result in severe fasciation in vigorously growing ‘Ai-Berry’ plants.
Flower color patterns are attractive traits of floricultural plants. However, the mechanisms underlying these traits remain mostly unknown. Carnation (Dianthus caryophyllus L.) and interspecific hybrids thereof exhibit many flower color patterns involving white margins on reddish petals, as observed in the cultivar ‘Minerva’. Flowers with white margins also have white abaxial surfaces. We studied the factors regulating the formation of white margins and a white abaxial surface in flowers through analyses of pigments and related gene expression. HPLC analysis revealed an absence of anthocyanins in white margins, although the accumulation of other flavonoid pigments (flavonols) was almost identical between the dark-red central and white marginal regions of petals. RNA-seq analyses of the dark red central regions and white marginal regions of ‘Minerva’ petals resulted in the extraction of 18 genes related to anthocyanin biosynthesis and transportation, including some transcription factors, as candidate regulatory genes for the formation of white margins. Further analysis of the expression of these genes by real-time RT-PCR and a comparison of two white-margin-flowered cultivars and three red-unicolor-flowered cultivars indicated that the expressions of two bHLH transcription factor genes and seven structural genes were positively correlated with anthocyanin accumulation. Although DcbHLH1, which is a homolog of JAF13 in Petunia ×hybrida, was expressed in both flower color groups, DcbHLH2, a homolog of AN1, was expressed only in white-marginal-flowered cultivars. Moreover, in the petals of ‘Minerva’, the expression of those nine genes was repressed in the abaxial epidermal layer without red pigmentation conferred by anthocyanins. Therefore, we could postulate that the localized repression of both bHLH genes is involved in the formation of white margins in carnation petals by inducing the absence of anthocyanin synthesis and that the white abaxial surface of the petals may result from similar regulatory mechanisms. In particular, DcbHLH2 could act as a key gene because of its restricted expression only in cultivars with white-margined flowers.
Understanding the mechanism of N uptake is of key importance to manage N utilization efficiency. Hippeastrum is a popular geophyte, but its N absorption and translocation characteristics are still not well understood. Therefore, the objective of this study was to assess the effect of different N sources on growth, N uptake and N distribution in Hippeastrum. The experiment was set up in a completely randomized design (CRD) with four different N sources of equal N concentration, i.e., 1) 2.5 mM 15NO3− + 2.5 mM NH4+ as treatment 1 (T1), 2) 2.5 mM NO3− + 2.5 mM 15NH4+ as treatment 2 (T2), 3) 5 mM 15NO3− as treatment 3 (T3), and 4) 5 mM 15NH4+ as treatment 4 (T4). A 15N-labelled 30 mL nutrient solution was drenched on plant pots (per time per pot). Plants were supplied with the 15N solution every two weeks. Plant samples were divided into three stages according to plant growth stage, i.e., Stage 1 (emerging stage—1 WAP), Stage 2 (flowering stage—3 WAP), and Stage 3 (vegetative stage—15 WAP). The results indicated that plants fed with a combined N fertilizer and nitrate had a higher total dry weight than plants supplied solely with ammonium. At Stage 3, the plants supplied with 5 mM NO3− (T3) had a higher total N content than plants supplied with a mixed form of N (T1, T2) or solely NH4+ (T4). In addition, plants supplied solely with NO3− (T3) had a higher N distribution in leaves than plants supplied with a mixed N source (T1, T2) and solely NH4+ (T4). At 15 weeks after planting (Stage 3), a higher 15N use efficiency (15NUE) was observed in plants supplied with a mixed N source (T1, T2) and 5 mM 15NO3− (T3) in comparison with those supplied solely with NH4+ (T4). Scales were a major site of 15N distribution in Hippeastrum at Stage 1. Nevertheless, most 15N at Stage 2 and 3 was found in the roots + basal plate and leaves, respectively.
Roses are among the most widely produced cut flowers, with important ornamental and economic value in the flower market. In order to investigate how to regulate flowering periods, the negative regulator of GA biosynthesis RcSPY was cloned from Rosa chinensis and ectopically expressed in tobacco. The overexpression of RcSPY in SPY4 transgenic tobacco significantly increased plant height. Antisense interference with the conserved SPY domain of RcSPY led to GA accumulation in SPY5 transgenic tobacco plants, and antisense interference with the conserved TPR repeats of RcSPY resulted in late flowering in SPY6 transgenic tobacco plants. This result suggests that RcSPY is a negative regulator of GA biosynthesis, since the knock-down of RcSPY increased GA content. However, other phenotypes displayed by transgenic tobacco plants may not be caused by changes of GA content, but rather be the direct effects of RcSPY. Therefore, RcSPY not only participates in GA biosynthesis, but also plays a role in other vegetative and reproductive plant behaviors not related to GA. This result provides theoretical support for the molecular breeding of new cultivars of rose plants.
A torenia mutant, designated as “reddish purple shrunken” (RPS) because of its shrunken reddish-purple petals, was isolated from the S1 progeny of a “flecked” mutant containing an active DNA transposon Ttf1. Cyanidin-type anthocyanins—i.e., peonidin 3,5-diglucoside and cyanidin 3,5-diglucoside—were detected in petals of the RPS mutant, whereas delphinidin-type anthocyanins—i.e., malvidin 3,5-diglucoside, petunidin 3,5-diglucoside, and delphinidin 3,5-diglucoside—were the major anthocyanins in normal-type petals. Petal shrinkage could be attributed to this change in anthocyanin composition. A frameshift mutation in the first exon of flavonoid 3',5'-hydroxylase (TfF3'5'HΔC) inhibited biosynthesis of delphinidin-type anthocyanins in RPS. The “white” (W) mutant bore pure white petals in response to Ttf1 insertion in the first exon of the flavanone 3-hydroxylase gene (TfF3HTtf1). Some F2 plants derived from the cross between RPS and W bore reddish-purple petals without any shrinkage; these were designated as “reddish purple” (RP). This RP genotype was revealed as a heterozygote of TfF3H+ and TfF3HTtf1 in the background of the TfF3'5'HΔC homozygote. A gene dosage effect of TfF3H reduced anthocyanin biosynthesis in RP compared with RPS, whereas this decrease caused no reduction in visual color density. Therefore, a partial decrease in anthocyanin biosynthesis may be beneficial if petal shrinkage prevents using a new-color mutant for breeding.
The effects of pulse treatments with 0.2 mM silver thiosulfate complex (STS), 5 and 10% sucrose, and 0.2% calcium chloride (CaCl2) and their combinations on the vase life and soluble carbohydrate and aurone levels in cut snapdragon (Antirrhinum majus) flowers were investigated. In the pulse treatment, the cut flowers were treated with these chemical solutions for 24 h before being transferred to distilled water. The uptake of solution for pulse treatments was decreased in the treatments with STS, sucrose, and CaCl2 and the combined STS and sucrose treatment further suppressed uptake. The sucrose treatment significantly increased the number of open flowers and extended the vase life, with no marked differences in these effects between the 5% and 10% sucrose solutions. The STS treatment slightly promoted flower opening but did not significantly extend vase life. The CaCl2 treatment did not affect flower opening or vase life. The relative fresh weight (RFW) and water uptake of cut flowers were increased in the sucrose treatments and were only slightly affected by the STS and CaCl2 treatments. The petal aurone levels were significantly higher in the sucrose treatments, particularly at 10% sucrose. The glucose, fructose, and sucrose petal contents were generally higher in the sucrose treatments than in the treatments that did not include sucrose. The ethylene production of flowers was relatively low at harvest and somewhat increased during senescence. Therefore, the infectiveness of STS on vase life may be due to low ethylene production. We conclude that pulse treatments with solutions containing sucrose increase the sugar contents and aurone levels in petals, as well as improve the vase life of cut snapdragons.