The production of yellow-skinned apples has increased in recent years; however, they are less acceptable to consumers than red-skinned apples. Therefore, the production of high-quality fruit is essential. In the present study, we applied a girdling treatment at 1) different times (June or August), and 2) different widths (2 cm, 5 cm, and 8 cm). We compared the effect on tree growth, flower bud formation and fruit quality over a 4-year field trial using vigorous yellow-skinned ‘Koukou’ apple trees. The August girdling reduced the shoot growth by about 6 to 10 cm per shoot and this reduction also restricted secondary extension of the shoots. The August treatment improved the fruit quality parameters, including the soluble solids content and skin color index, more effectively than the June treatment. Compared with the girdling timing, the effect of girdling widths in August was less obvious, but even the 2 cm treatment in August was enough to reduce tree vigor and improve fruit quality. Apical flower bud formation was accelerated by the August girdling in both the treatment year and the following year. Regardless of the girdling width, the August girdling improved the fruit quality parameters: e.g. flesh firmness, soluble solids content, and skin color index. The August girding fruit also had higher sorbitol and sucrose concentrations than the control. Moreover, both the girdling treatments accelerated the incidence of watercore, which is a preferred condition for the Asian market. In conclusion, we found that all widths of girdling in August improved the harvested fruit qualities, including the sugar (sucrose) content, as well as watercore development in the treatment year and effectively controlled tree vigor, increased flower bud formation and increased yields.
Tomato grafting is an important agricultural technique to overcome biotic and abiotic stresses and increase plant growth and productivity. Breeding and selection of resistant and vigorous rootstocks are necessary to achieve grafting goals. Therefore, this study was conducted to evaluate eight tomato interspecific hybrids between accession Solanum lycopersicum L. LA1221 ‘VFNT cherry’, as the female parent and each of wild accessions S. chmielewskii LA1028 (Chm-1028); S. galapagense LA0530 (Gal-530); S. habrochaites CGN 15391 (Habr-15391) and LA1777 (Habr-1777); S. pennellii AusTRCF 312075 (Pen-312075) and LA716 (Pen-716); and S. pimpinellifolum AusTRCF311810 (Pim-311810) and CGN18388 (Pim-18388), as male parents, as rootstocks under greenhouse conditions compared to the commercial rootstock ‘Emperador’, to select the most suitable rootstock. S. lycopersicum ‘Santa Cruz Piedade’ was selected as a scion and used as self-grafted and non-grafted controls. Plant growth and productivity measurements were estimated for the grafted and non-grafted plants. The response to the evaluated rootstocks was not consistent for many of the studied traits, denoting that the scion was differently influenced by the rootstocks. Grafts did not always outperform self-grafts. Grafting onto either Pen-312075, Habr-15391, or Pim-18388. in addition to self-grafting, increased the total and marketable yields compared to the non-grafted plants, with proportions that would enable increased profits and cover the extra cost of grafting. In addition, fruits from these grafts had acceptable quality traits. Therefore, the interspecific hybrids Pen-312075, Habr-15391, and Pim-18388 are considered suitable rootstocks to improve the scion ‘Santa Cruz Piedade’. Greater and continuing efforts are needed to evaluate several interspecific hybrids, as well as different high yielding scion cultivars, to select the most suitable rootstocks for different scion cultivars.
Yield optimization of young Japanese ‘Nanko’ apricot (Prunus mume Siebold et Zucc.) trees requires adequate and timely irrigation. Here, different irrigation amounts (5, 10, 15, and 20 mm) were applied to three-year-old trees from July (initiation of flower bud differentiation stage) to March (fruit setting stage), when the pF meter reading was 2.7. Then, the effects on flower buds and fruit setting rate were assessed. Trees supplied with the 5 and 10 mm irrigation amounts experienced severe drought stress. Limited water supply reduced flower-bud growth and flower-bud number, possibly caused by several factors including inhibition of flower-bud differentiation in summer and abscission of immature buds just before anthesis. Limited irrigation did not inhibit complete flower formation, except under the 5 mm irrigation treatment, but flower size and fruit-setting rate were negatively affected. These findings indicated that insufficient irrigation caused poor flower formation and low fertility. Combined, these effects explained the observed yield reduction and all irrigation treatments, except for the 20 mm one, severely affected productivity. Based on these results, we recommend that the amount of water applied to young Japanese apricot trees from flower-bud differentiation to fruit set should be no less than 20 mm to achieve adequate flower bud growth and a high fruit-setting rate for high fruit yield.
The sacred lotus (Nelumbo nucifera) is an aquatic basal eudicot that is widely cultivated for food, medicine, and ornamental use. Ornamental lotus cultivars form flowers of various colors and shapes. The ABCE model for flower development has been proposed for model core eudicots such as Arabidopsis and snapdragon, but little is known about the molecular mechanisms of floral organ specification and development in N. nucifera. Here, we identified ABCE-class genes in the N. nucifera genome and compared their gene structures and spatial expression patterns in floral organs between single- and double-petalled flower-type lotus cultivars. Two lotus homologs of the C-class gene AGAMOUS (NnAG1, NnAG2) in a double-petal flower cultivar had intact transcripts, suggesting that loss of function of AG is not the cause of the double-petal phenotype in N. nucifera. NnAG1 and NnAG2 expression were specifically observed in stamens and carpels of a single-petalled flower cultivar, but were slightly reduced in the double-petalled flower cultivar. In situ hybridization analysis further revealed that these two C-class homologs are specifically expressed in inner whorls such as stamens and carpels in a single-petal flower cultivar, but the signals are diminished in double- and proliferating-petalled cultivars. These findings suggest that down-regulation of C-class genes is responsible for the multiple-petal phenotype in N. nucifera.
Ornamental foliage plants are valued for their catchy leaves with diverse shapes and colors, but dark-induced plant senescence or deterioration during transport greatly limits the quality of foliage plants. Melatonin is an important signaling molecule that affects pleiotropic developmental progress in plants. Aminoethoxyvinylglycine (AVG) is a potent inhibitor of ethylene biosynthesis and is extensively used to delay plant senescence and fruit ripening. In this study, we compared the effects of melatonin and AVG on alleviating plant deterioration of three Pilea species (P. cadierei (PC), P. involucrata (PI), and P. mollis (PM)) through foliar sprays of different concentrations of melatonin or AVG prior to darkness treatment. Our results showed that PC, PI, and PM exhibited distinct responses to melatonin or AVG. PM was the most sensitive species and it exhibited significant increases in stem height, leaf area, chlorophyll, and anthocyanin content in response to 50, 100, and 150 μmol·L−1 of melatonin; similar responses to 150 and 200 μmol·L−1 of melatonin were observed in PI with regard to these plant characteristics. By contrast, much weaker effects of AVG on these plant characteristics were observed in PM and PI, although it increased their Fv/Fm values as did melatonin. Unlike PM and PI, PC is generally not responsive to all melatonin and AVG treatments, although AVG treatments did change its stem elongation. These results may provide growers with science-based information for future practical application of melatonin to improve the post-harvest quality of ornamental plants.
Tomato (Solanum lycopersicum) productivity is negatively impacted by extreme weather events such as heatwaves, flooding and drought. This study evaluated the individual and additive effects of heat and water stress on reproductive traits and yield in the commercial tomato variety ‘Roma-VF’. Five weeks after sowing, five stress treatments were introduced consisting of combinations of heat and/or moderate and severe water stress. Heat-stressed plants were subjected to day/night temperatures of 35/23°C, and the control of 28/20°C. Moisture stress was imposed by natural depletion of soil water to 70% and 40% of field capacity (moderate and severe stress, respectively). After eight weeks of treatments, plants were placed under control conditions for a five-week recovery phase. Pollen morphology, number of flowers, fruits, and aerial biomass were recorded. Flowers from plants subjected to heat stress combined with either moderate or severe moisture stress did not produce any pollen during the treatment period. Further, by the end of the recovery period, 27–38% fewer fruits matured on plants subjected to either heat or moisture stress, while fruit production among plants subjected to both stresses simultaneously declined 90% relative to the control (P < 0.001). We conclude that the ‘Roma-VF’ tomato will be able to recover adequately from heatwaves provided plants are well irrigated. However, should heat and moisture stress co-occur, fruit yield is likely to be decimated and recovery is unlikely. This study is also the first report on additively combined effects of heat and water stress on the ‘Roma-VF’ tomato.
Intumescence injury of tomato leaves is a physiological disorder in which white surface spots rise on the abaxial side of the leaf and then turn brown; when it worsens, the leaf dies. Scanning electron microscope observations showed individual cells were enlarged and raised due to intumescence injury. Vein epidermal cells and stomatal guard cells were also enlarged. Hypertrophy was observed by light microscopy in epidermal cells, spongy tissue cells, and palisade tissue cells. In thin leaf sections prepared with Technovit 7100 resin, the resin peeled from the epidermal surface on the adaxial and abaxial sides of normal leaf areas. However, resin did not peel off from the enlarged epidermis in areas of intumescence. Transmission electron microscopy imaging of the cuticular layer in the epidermal cells affected by intumescence injury showed disappearance of the outermost wax layer, abnormalities in intermediate layer, and decrease in cuticular layer. Toluidine blue O staining was used to identify abnormalities in the cuticular layer and the area of intumescence, which was stained purple. The percentage of staining area relative to total area of the leaf was used to quantify the degree of intumescence. In experiments using incubators under low-UV conditions, intumescence injury was less likely to occur in young leaves or fully expanded leaves and more likely to occur in expanding leaves. In addition, the water content of the leaves in which intumescence injury occurred was lower than that in normal leaves. Intumescence injury occurred less frequently under conditions of 70% relative humidity than under conditions of 90% relative humidity. UV and relative humidity are known to affect the development of the cuticular layer, and intumescence injury was severe under conditions in which the cuticular layer had difficulty developing. Our findings showed that intumescence injury of leaves was accompanied by abnormal cuticular layer, and suggest that occurrence of intumescence injury may be reduced under conditions in which the cuticular layer is well developed, such as with UV irradiation and low relative humidity.
To elucidate the profiles of plant hormones involved in growth and ripening of grape fruit at various stages, grape bunches of Campbell Early grape bunches (Vitis labrusca ‘Bailey’) which were harvested from 14 to 63 days after full bloom (DAFB) were divided into skin, pulp and seeds. Endogenous plant hormones, which included indole-3-acetic acid (IAA), abscisic acid (ABA), trans-zeatin (Z), isopentenyl adenine (iP), jasmonic acid (JA), methyl jasmonate (MeJA), gibberellin1 (GA1), and gibberellin4 (GA4), were quantified by liquid chromatography-mass spectrometry (LC-MS). Throughout the sampling period, higher IAA concentrations were maintained in the seeds than those in the skin and pulp. In the seeds, the Z concentration was highest at 14 DAFB and then decreased rapidly. However, in the skin and pulp, the iP concentration increased over the course of sampling. The ABA concentration in the pulp was high around veraison. The JA concentration in the skin reached 4,100 pmol·g−1FW at 27 DAFB. The MeJA concentration in the skin also increased rapidly. These results suggest that increases in iP concentration in the skin and pulp are involved in maturation.
Cut astilbe (Astilbe × arendsii) inflorescences have many small florets with low ethylene sensitivity, and a short vase life. The senescence of flowers is complex and probably regulated by programmed cell death, but specific senescence-related genes have not been widely studied, apart from ethylene-sensitive species. In this study, we investigated the effects of continuous treatments with 4% sucrose (Suc), 2% trehalose (Tre), and a combination (Suc+Tre) on postharvest quality and senescence-related gene expression in cut flowers of the astilbe ‘Gloria Purpurea’. Vase life was extended from 3.7 days to 10.3, 9.4, and 12.4 days by treatment with Suc, Tre and Suc+Tre, respectively. Florets were sampled at 0 days (0 d) and 2 days after harvest (2 d). De novo RNA-sequencing (RNA-seq) of floret tissues produced 89,705 unique sequences, and 2,517, 979, 609, and 1,846 differentially expressed genes were identified from the 0d_Control (Cont) vs. 2d_Cont, 2d_Cont vs. 2d_Suc, 2d_Cont vs. 2d_Tre, and 2d_Cont vs. 2d_Suc+Tre libraries, respectively. Gene Ontology (GO) analysis indicated that expression of many photosynthesis-related genes was upregulated in 2d_Cont florets, suggesting the photosynthesis system is activated in senescing florets. Kyoto Encyclopedia of Genes and Genomes analysis showed that WRKY22, related to leaf senescence, was more highly upregulated in 2d_Cont compared with 0d_Cont, 2d_Suc, and 2d_Tre in the Mitogen-activated Protein Kinase (MAPK) signaling pathway. Using Fragments Per Kilobase per Million reads (FPKM) values from RNA-seq, candidate genes associated with senescence including the no apical meristem, ATAF1/2 and cup-shaped cotyledon transcription factor 29 (NAC029), senescence-associated gene 12 (SAG12), and peroxidase 21 (PER21) were selected. Suc+Tre in particular, the most effective treatment for prolonging vase life, downregulated NAC029, SAG12, and PER21 expression at 2 d. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) validated the RNA-seq results, i.e., similar expression trends were found in the three genes, although relatively weak expression levels were detected compared with FPKM values from RNA-seq. The effect of Tre alone on the three genes’ expression levels was relatively small compared with treatments containing Suc, suggesting that Tre may delay floret senescence by altering genes involved in water transport such as Aquaporin tonoplast intrinsic protein 1-3. This study revealed several candidate genes and GO terms involved in the senescence of cut florets, but further study is needed, especially on key genes including NAC029 and WRKY22.
To date, different approaches have been applied to measure the internal parameters of mangoes by destructive and non-destructive techniques. Recently, real-time evaluation of the internal parameters has become important assessment for fruits in high demand. This research aims to develop an online prototype system to measure the total soluble solids (TSS) in mangoes using a fiber optic diode array Visible-Near Infrared (Vis-NIR) spectrometer on a conveyor belt. Spectra were acquired in a wavelength range from 400–1000 nm. The diffuse reflectance spectra of mangoes were subjected to several preprocessing techniques such as moving average smoothing (MAS), standard normal variate (SNV), multiplicative scatter correction (MSC), baseline offset and normalization before model development. The spectral information and corresponding TSS values were used to establish a linear relationship by partial least squares (PLS) regression. Spectra in three wavelength ranges of 400–1000 nm, 600–1000 nm, and 700–1000 nm were used for the model development. Baseline offset combined with MAS showed effective transformation of spectra at a wavelength of 600–1000 nm. The optimum model was obtained by an external validation technique with a correlation coefficient of calibration set and a prediction set of 0.80 and 0.74, respectively. The root mean square error of the calibration (RMSEC), root mean square error of prediction (RMSEP) and bias were 0.690%, 0.765%, and 0.061%, respectively. The statistical results from PLS regression indicated the feasibility of using the online conveyor system for grading the fruit according to the TSS.
Cultivated strawberry is one of the important commercial fruits not only in Japan, but around the world. Even so, analyzing regions responsible for fruit quality traits of cultivated strawberry has been very challenging due to the alloploidy and octoploidy of genome conformation. In order to solve this problem, we previously developed a strawberry multi-parent advanced generation inter-cross (MAGIC) population derived from crosses involving six cultivars. Here, we performed genotyping of the MAGIC population with simple sequence repeat (SSR) markers, which were generated from an expressed sequence tag site, and conducted a genome-wide association study of 13 strawberry fruit quality-related traits to reveal associated quantitative trait loci (QTLs). Correlation coefficients among fruit color-related traits, such as fruit surface color (FSC), fruit surface anthocyanin content (FSA), and fruit flesh anthocyanin content (FFA) were relatively higher, but FSC, FSA, and FFA did not show any higher correlation with other traits. Fruit weight (FW), FSC, and fruit firmness, including whole fruit firmness (WFF), fruit surface firmness (FSF), and fruit flesh firmness (FFF), indicated higher year to year correlation coefficients than other fruit quality-related traits. Among FW, FSC, and WFF, there were only two QTLs for FW, five for FSC, and 38 for WFF (the most) and they were detected on all chromosomes. QTLs for some traits shared common flanking simple sequence repeat markers, and allelic differences of one marker affected the variation of other traits. QTLs for fruit firmness were most frequently detected, followed by those for SSC and titratable acidity (TA). Allelic differences in these QTLs negatively affected FSC, the fruit surface anthocyanin content (FSA), and fruit flesh anthocyanin content (FFA), implying that alleles which increase fruit firmness, SSC, and TA lighten fruit color. Similarly, QTLs for FSC, FSA, and FFA mostly negatively affected FSF, FFF, SSC, and TA and did not affect WFF. This indicated that simultaneous improvement in fruit firmness, SSC, and TA is possible with many markers, but improving fruit firmness and deepening fruit color are highly challenging.
Onion (Allium cepa L.) is one of the most important vegetable crops worldwide. In Japan, it is grown using two different cultivation methods (spring-sowing and autumn-sowing). The traditional cultivation method for onion in the Tohoku region in northeast Japan has been autumn sowing; however, onion productivity has been low. Recently, spring sowing of onion has been established in this region to improve onion productivity in the off-crop season. To better understand the spring-sowing cultivation method, we examined the plant growth and bulb development of eight commercially-grown onion cultivars (‘Turbo’, ‘Aurora’, ‘Momiji No. 3’, ‘Marso’, ‘Okhotsk 222’, ‘Kitamomiji 2000’, ‘Super Kitamomiji’, and ‘Gunnison’) throughout the growth period. The results showed that this cultivation method enabled us to grow and compare relatively long-day and intermediate-day cultivars at the same time, under the same environmental conditions. Onion bulb development was induced and persisted during long day-lengths and was inhibited by short day-lengths which were longer or shorter than the critical day-lengths for bulb development of each cultivar. To elucidate this mechanism, expression analysis of AcFTs related to bulb development was conducted. Our expression analysis showed that AcFT1 was expressed in accordance with the maturity of the cultivars, and this gene expression can be used as an index for maturity types of the cultivars and bulb development. The results indicate that onion responds to a critical day-length for bulb development and starts bulb development before the bulbing ratio greatly exceeds 2. This metric can be used as an index of bulb development.
Red mangos (Mangifera indica L.) accumulate appreciable amounts of cyanidin-based anthocyanins in the skin, and previous studies showed that these anthocyanins contain galactose as a sugar moiety. To date, two UDP:flavonoid 3-O-glycosyltransferase (UFGT)-like genes named MiUFGT1 and MiUFGT3 (MiUFGalT3) have been isolated from mango ‘Irwin’ peel as anthocyanin-related UFGT genes, but the function of the proteins of the genes have not yet been elucidated. In this study, we characterized recombinant MiUFGT1 and MiUFGalT3 expressed in Escherichia coli. In the presence of quercetin as an acceptor, rMiUFGT1 showed marginal glucosylation activity, while rMiUFGalT3 exhibited significant galactosylation activity 20-fold higher than its glucosylation activity. Specificity analysis using purified MiUFGalT3 found that rMiUFGalT3 almost equally accepts anthocyanidins and flavonols. The anthocyanins extracted from the ‘Irwin’ skins were cyanidin 3-O-galactoside and 7-O-methylcyanidin 3-O-galactoside by instrumental analyses, which is consistent with previous results obtained for other red mango cultivars. The results suggest that MiUFGalT3 is responsible for the red coloration of ‘Irwin’ mango fruit skins.
Heat-induced flowering delay of Chrysanthemum morifolium is a major problem affecting the production of cut flowers in Japan. Understanding the delay mechanism is indispensable to achieve stable production. Heat sensitivity has been shown to fluctuate throughout the day, as if it is regulated by a circadian clock. This paper studied the involvement of a circadian clock and photoperiod in the fluctuation of heat sensitivity throughout the day by applying pulses of heat at different times to Chrysanthemum seticuspe and Chrysanthemum morifolium under different regimens of light and dark. One experiment examined the elevation of heat sensitivity under different photoperiods in order to determine whether the transition from light to dark or vice versa serves as a signal for a clock-like regulation of heat sensitivity. Maximum heat sensitivity was frequently observed at a constant interval after light-off, but not after light-on, identifying the transition to darkness as the signal that initiates the elevation mechanism. We also examined the descending phase of heat sensitivity. Heat sensitivity peaked approximately 16 h after light-off and then gradually declined under dark conditions, suggesting an endogenous clock-controlled fluctuation. We further studied the effect of light on elevated sensitivity by conducting trials with dark periods of 13 or 16 h. Sensitivity peaked at both 10–13 and 13–16 h after light-off under the 16 h-dark condition, but only at 10–13 h after light-off under the 13 h-dark condition, indicating a rapid decline in heat sensitivity induced by light supplied 13 h after light-off. Results of the three experiments suggest that the daily elevation in heat sensitivity is potentially controlled by an internal clock that is reset by a transition from light to dark. A subsequent transition to light appears to eliminate elevated sensitivity. From this, we conclude that heat sensitivity is maximized toward the end of the night, irrespective of photoperiod, in chrysanthemums.
Cymbidium is one of the largest orchid genera and it is famous for its ornamental, cultural, and economic value. Many Cymbidium species have an elegant flower fragrance, including C. faberi, C. goeringii, C. ensifolium, C. kanran, C. sinense, and so on. Although the components of the flower fragrance have been identified in many orchids, the molecular mechanism of their formation and regulation has not been explored. As one of the main components of flower fragrance, methyl jasmonate (MeJA) has been selected and the biosynthesis pathway was elucidated in some Cymbidium orchids. In order to modify the traits of flower fragrance in Cymbidium orchids, the underlying regulatory mechanisms need to be identified. In this study, four MYB transcription factors screened from RNA-seq results of C. faberi were successfully cloned and molecularly characterized. The activation of these CfMYBs with CfAOC and CfJMT promoters suggested that they may participate in the regulation of MeJA formation in C. faberi. This result could provide molecular support for the genetic modification and breeding of new C. faberi cultivars.