The thinning of flowers or fruit is an essential part of the commercial production of quality apples. Although chemical thinners are generally used in apple orchards throughout the world, hand-thinning remains essential for controlling crop load to improve fruit quality and return bloom. The objectives of this study were to investigate factors that determine the time required for hand-thinning and to elucidate cultivar-related efficiency of hand-thinning. In all cultivars, the time taken for hand-thinning per cluster became shorter after petal fall, but the degree of this decrease differed among cultivars. The time taken for hand-thinning depended on both how much and when natural abscission of fruitlets occurred. The times required for hand-thinning were very similar among clusters with four, five, or six flowers/fruitlets, which was twice as long as that required for clusters with two or three flowers/fruitlets. This means that the time required for hand-thinning clusters is critically reduced when the number of flowers/fruitlets within a cluster is three or fewer. The time required for hand-thinning clusters of axillary buds became significantly longer from bloom to 7 days after bloom, and then decreased gradually from 7 to 25 days after bloom. When the proportion of clusters with three or fewer fruitlets is 50% at 15 days after bloom, the planting area of the cultivar that a person is able to hand-thin (six hours per day) from 10 to 30 days after bloom was 24.3 a, which was 40% larger than that of a cultivar in which the proportion of clusters with three or fewer fruitlets is 50% at 30 days after bloom (17.4 a). Therefore, the introduction of cultivars in which fruit abscission occurs at an early stage and on a large scale is a solution for reducing the labor costs of hand-thinning.
Cryopreservation has become a very important tool for the long-term storage of plant germplasm. A new cryopreservation protocol based on air dehydration of explants placed on aluminum cryo-plates, termed the D cryo-plate technique, was developed. In this study, the most suitable conditions of cryopreservation for dormant shoot tips of Japanese persimmon (Diospyros kaki Thunb. ‘Saijo’) using the D cryo-plate technique were investigated. Dormant one-year-old shoots of persimmon were collected from the experimental farm of Shimane University in January 2013 and stored at 2°C until use. After surface sterilization, shoot tips of about 1 mm in size were dissected from the dormant buds and precultured overnight at 25°C on solidified 1/2MS medium containing 0.3 M sucrose. Precultured shoot tips were placed on aluminum cryo-plates and embedded in calcium alginate gel. Osmoprotection of shoot tips was performed by immersing the cryo-plates for 30 min at 25°C in an LS solution containing 2 M glycerol + 1.0 M sucrose in 1/2MS solution. For the D cryo-plate technique, encapsulated shoot tips were dehydrated by placing the cryo-plates in the air current of a laminar flow cabinet for 30–90 min. Cooling was performed by placing the cryo-plates in uncapped cryotubes, which were immersed in liquid nitrogen. For rewarming, the cryo-plates were immersed in 1/2MS medium containing 1.0 M sucrose for 20 min at 25°C. In this study, the preculture did not improve the regrowth after cryopreservation; however, we consider that it should be performed in the D cryo-plate procedure for application of other cultivars and utilization in genebanks. A high regrowth rate of cryopreserved shoot tips (84%) was achieved after dehydration for 30 min. This optimized procedure was applied to 10 additional persimmon cultivars, resulting in regrowth rates ranging between 67 and 97%, with an average of 87%. As shoot tips derived from dormant buds proved to be highly tolerant to liquid nitrogen exposure, the D cryo-plate technique may facilitate long-term conservation of persimmon germplasm.
To investigate the mechanism of yield increase by elevated carbon dioxide (CO2) and fogging in Japanese tomato cultivars (Solanum lycopersicum), total above-ground dry matter (TDM), fraction of dry matter distribution to fruit (FDF), and photosynthetic characteristics were measured in 3 Japanese cultivars grown in elevated CO2 with fogging and ambient CO2 without fogging. Fresh fruit yield and TDM were improved by the elevated CO2 and fogging in the 3 Japanese cultivars. Light use efficiency (LUE) was also increased by the elevated CO2 and fogging. No significant decrease in FDF was observed by the elevated CO2 and fogging in 2 Japanese cultivars, ‘Asabiyori 10’ and ‘Junkei Aichi Fast’. Thus, the increase in TDM by higher LUE contributed directly to the yield increase in these 2 cultivars. However, FDF in ‘Momotaro York’ was decreased significantly by the elevated CO2 and fogging. Thereby, the yield increase by the elevated CO2 and fogging was diminished in ‘Momotaro York’ in spite of the increase in TDM. The number of trusses having immature fruit in ‘Momotaro York’ under elevated CO2 and fogging was significantly higher than those of the others, although no increase in the number of trusses having immature fruit was observed in the other 2 cultivars. Although vegetative growth characteristics such as leaf area, LAI, and fresh and dry weights of leaves and stem were increased by the elevated CO2 and fogging, no negative effects such as a change in light-extinction coefficient and a decrease in maximum photosynthetic rate were observed. The elevated CO2 and fogging increased the number of harvested fruit but decreased weight per fruit, namely, fruit size, in the 3 cultivars.
This study evaluates the effect on the ‘Splendor’ and ‘Primoris’ strawberry cultivars of different dates of inoculation with Glomus intraradices, an arbuscular mycorrhizal (AM) fungus. Additionally, plants were grown in a soilless growing system with or without Bacillus velezensis at the beginning of the experiment. A completely randomized block design (2 biofertilizer treatments × 2 cultivars × 3 inoculation dates) with 2 replications was used. Each replicate consisted of one bag with 10 plants. Fruit weight, fruit quality, growth parameters, and SPAD values in young leaves were monitored from October 2011 to June 2012 in a greenhouse. At the end of the crop cycle, the microbial population of Bacillus spp. and the Glomus intraradices population were determined from the rhizosphere of the plant. Bacillus velezensis and Glomus intraradices were established in the strawberry soilless growing system. The effect of arbuscular mycorrhizae on strawberry fruit quality was more important than that on growth parameters. Biofertilizer with arbuscular mycorrhizal fungi had an inhibitory effect on fruit quality, as indicated by low TSS, pH, and TA values. The combined effect of the biofertilizer and inoculation dates of Glomus intraradices on growth parameters was more significant in the ‘Primoris’ cultivar than in ‘Splendor’. In both cultivars, an increase in SPAD values was observed from week 12 to week 22 after planting. Depending on the cultivar selected, the date of inoculation may significantly affect plant response to AM fungal colonization in a soilless growing system.
A full-length cDNA of a putative flavonoid 3'-hydroxylase (F3'H) gene encoding a key enzyme in the production of cyanidin was cloned from a lisianthus (Eustoma grandiflorum) petal. Lisianthus F3'H (EgF3'H) shares 75.1, 73.8, and 68.2% amino acid identity with Arabidopsis thaliana, Ipomoea nil, and Petunia hybrida, respectively. RT-PCR revealed that wild-type lisianthus flowers accumulated higher levels of F3'H mRNA during the early stages of development than in the late stages. The accumulated F3'H transcript levels in leaves were similar to those in flowers in the early stages of development. Overexpression of lisianthus F3'H cDNA altered flower color from red to blue in the I. nil cultivar ‘Violet’, which lacks a functional F3'H gene. In addition, the transgenic ‘Violet’ plants accumulated cyanidin and peonidin at similar levels to wild-type I. nil. Taking these findings together, this study demonstrates that EgF3'H functions as a flavonoid 3'-hydroxylase with a role in the synthesis of cyanidin and peonidin pigments.
Several kinds of double-flowered cultivars have been produced from spontaneous mutants in Cyclamen persicum Mill. The morphology and number of organs in double flowers were investigated, and were categorized into three types: “petaloid-stamen type”, “petaloid-sepal type”, and “extra petals in whorl 2 type”. Morphological observations showed that petaloid mutations of stamen and sepal did not appear together within an individual. In addition, three types of AG-like gene were isolated from single and petaloid-stamen-type double-flower buds, and expressions in each whorl were compared. All AG-like genes were expressed in whorl 3 of single flowers, but not in that of petaloid-stamen-type double flowers. In whorl 4, although expressions of the three types of AG-like gene were observed in both single and double flowers, the expression of double flowers was lower than that of single flowers. These results suggest that naturally occurring double flowers of cyclamen can be explained by the ABC-model, and it is suspected that petaloidy of the stamen is caused by the repression of AG-like gene expression in whorl 3.
Flowers of Eustoma grandiflorum open in the morning and close in the evening, showing diurnal rhythms. In this study, the process of flower opening and closure of E. grandiflorum ‘Azuma-no-Murasaki’ was examined under different light cycles by capturing corolla images using interval photography. At 24-hour light cycles, the flower opening rhythm synchronized with the light cycles, and the process was composed of dual steps. The first one was immediate opening and closure at the times of initiation and cessation of the light period, respectively. The second one was gradual opening and closure, which occurred 12 hours after the end of the former light period and 2–3 hours after the initiation of the current light period, respectively. The first response appeared to be a direct effect of light, while the second one appeared to be under the regulation of circadian clocks. Under constant dark, blue, or red conditions, flowers showed circadian oscillations of 25.5 ± 0.6, 25.6 ± 0.6, or 24.3 ± 0.4 hours, respectively. Under constant white light or co-irradiation of blue and red light, flowers opened and closed once, but the oscillations did not continue thereafter. The synchronization of flower opening and closure rhythms to 24- and 20-hour day cycles was observed for both blue light and red light cycles. The synchronization was not complete for 16-hour light cycles and the flower oscillation period became 24 hours under 12-hour light cycles. The direct effect of light was found to be dependent on light intensity. When blue light intensity was adjusted at 25, 40, or 100 W·m−2, flowers opened more rapidly after illumination at a stronger light intensity, but such intensity-dependent effect was not observed for red light.
The relationship between transpiration from the inflorescence and the vase life of cut hydrangea ‘Endless Summer’ flowers was studied. In the defoliated cut flowers, the vase life increased with a decreasing number of decorative florets. Cut flowers having small inflorescences with 189 decorative florets exhibited a lower level of transpiration (7 g·day−1) and longer vase life (15 days) than those having large inflorescences with 422 decorative florets. The stomatal conductivity of the decorative sepals was very low, ranging from 2.7 mmol·m−2·s−1 to 3.3 mmol·m−2·s−1, and approximately 6% of the stomata were observed to be open microscopically. In addition, diurnal change of transpiration from a defoliated cut flower was not observed. These observations indicate that most of the transpiration from the sepals is through cuticular transpiration. The use of defoliated cut flowers that do not bear too many decorative florets and treatments that suppress transpiration from the surface of the decorative sepals would be effective for the vase life extension of cut hydrangea flowers.
The effects of glycine betaine (GB) under heat stress conditions were studied in three marigold cultivars, namely, ‘Narai Yellow’, ‘Bali Gold’, and ‘Columbus Orange’. GB was foliarly applied to the seedlings 24 hours before transfer to either 25°C/25°C or 39°C/29°C (day/night) conditions for 15 days. Heat stress conditions caused photoinhibition and low levels of CO2 assimilation rate (A), stomatal conductance (gs), and transpiration rate (E) in all marigold cultivars compared with those of control plants grown under 25°C/25°C conditions. The accumulation of reactive oxygen species (ROS), lipid peroxidation, and cell death were also higher under heat stress in all cultivars compared with those in the control. However, the effect of heat stress on relative water content (RWC) was statistically significant only in ‘Bali Gold’. Foliar applications of GB at 0.5 and 1 mM alleviated photoinhibition and resulted in higher A, gs, and E in all marigold cultivars compared with those in the control under heat stress. Application of GB also resulted in lower levels of hydrogen peroxide, superoxide, lipid peroxidation, and cell death in all cultivars. The effect of GB on improving RWC was significant only in ‘Bali Gold’. In most cases, there were no significant differences between the effects of GB at 0.5 and 1 mM. The effect of GB seems to be very consistent across all marigold cultivars, as suggested by the lack of interaction between this effect and cultivars in most of the parameters that were studied. Overall, these results indicate that the foliar application of GB could possibly be used to mitigate the effect of heat stress in marigold.
2,4-Pyridinedicarboxylic acid (2,4-PDCA) was shown to prolong the vase life of cut flowers of spray-type ‘Light Pink Barbara’ (LPB) carnation, mainly due to the reduced ethylene production caused by inhibition of 1-aminocyclopropane-1-carboxylate oxidase in the flowers. In addition, 2,4-PDCA has been suggested to accelerate flower opening in the flowers (Satoh et al., 2014). In the present study, we successfully developed a procedure to evaluate the activity of chemicals to accelerate flower (bud) opening by determining the shortened time (in days) to flower opening. Using this procedure, we could show the activities of several PDCA analogs to accelerate flower opening, in addition to their already-known activity to extend the vase life in cut flowers of ‘LPB’ carnation. Judging from their effectiveness in the acceleration of flower opening and extension of vase life, 2,3-PDCA and 2,4-PDCA were thought to be suitable agents for treatment of the flowers. The present study confirmed that PDCAs accelerate flower opening and retard senescence, which increase the number of open flowers, resulting in extension of the vase life of cut flowers of ‘LPB’ carnation.