Haskap (Lonicera caerulea subsp. edulis) is a deciduous shrub that produces blue-black edible berries with a sour-sweet taste. By expanding fruit color variation, the value of agricultural products is enhanced. Interspecific hybrids were obtained from crossings between Haskap and red-fruit bearing Miyama-uguisukagura (Lonicera gracilipes). The fruit color of the interspecific hybrids obtained was red-purple. Fruit color in Haskap is mainly affected by the concentration of anthocyanin. However, there are no reports on the chemical determinants of fruit color in interspecific hybrids between Haskap and Miyama-uguisukagura. We evaluated anthocyanin components in these hybrids and their parents using liquid chromatography/tandem mass spectrometry, and revealed the presence of five different kinds of anthocyanins. The major anthocyanin in interspecific hybrids and Haskap was cyanidin 3-glucoside, while in Miyama-uguisukagura, it was cyanidin 3,5-diglucoside. Some genotypes among interspecific hybrids showed higher concentrations of cyanidin 3,5-diglucoside and peonidin 3,5-diglucoside, compared with their parents. The genotypes of interspecific hybrids and the parents were evaluated by principal component analysis of anthocyanin concentration. Our study contributes to the identification of anthocyanin composition in fruits of interspecific hybrids and in expanding fruit color variation when breeding new varieties.
This study was conducted to investigate the effects of different temperature treatments on kumquat fruit development and qualities. Kumquat trees were placed in growth chambers at day/night temperatures of 36°C/28°C, 28°C/20°C, and then 20°C/12°C two weeks after the first physiological fruit drop. The results showed that there was a positive correlation between temperature and fruit drop. The total fruit drop rate increased with temperature. The group at 36°C/28°C had the highest total fruit drop rate of 63.7%. High temperature (36°C/28°C) suppressed kumquat fruit growth. With increases in temperature, the lengths and diameters of fruits decreased. Moreover, the kumquat peel color in the 36°C/28°C and 28°C/20°C groups did not change from green to orange. High day/night temperatures (36°C/28°C) during fruit growth stages suppressed fruit growth and could reduce fruit quality. Low day/night temperatures (20°C/12°C) prolonged the fruit development period, increasing fruit size and allowing peel color to change successfully. In order to avoid fruit drop caused by high temperatures at the fruit setting stage, pruning in early February is recommended.
The present experiment was conducted to determine whether water extracts of lemon balm and oregano could suppress anthracnose in strawberry and to identify the important secondary metabolites responsible for such activity. Runner plants of three strawberry cultivars (Fragaria × ananassa Duch. ‘Sachinoka’, ‘Akihime’, and ‘Tochiotome’) were treated with water extracts (20%, w/v) of lemon balm (Melissa officinalis L.) and oregano (Origanum vulgare L.) separately and inoculated with Colletotrichum gloeosporioides (C. fructicola, CG1). Two weeks after CG1 inoculation, it was observed that the shoots and roots of the herb extract-treated plants had lower disease incidences and indices compared to those of the control regardless of the cultivar. Consequently, dry weights of the shoots of all the cultivars treated with the herb extracts were observed to be heavier than in the control; similarly, heavier dry weights of roots were also observed in herb extract-treated plants in ‘Sachinoka’ and ‘Tochiotome’. Upon analyzing the results of ultra-performance liquid chromatography-tandem mass spectrometer (UPLC-MS/MS), rosmarinic acid and luteolin in lemon balm and apigenin and protocatechuic acid in oregano were identified to be the metabolites with the highest concentration in their respective plants. In addition, the antifungal effect of all these compounds against CG1 was confirmed by in vitro tests. Thus, it can be concluded that water extracts of lemon balm and oregano could suppress anthracnose in strawberry plants, and the four identified compounds in the extracts could play key roles in the antifungal properties of these herbs.
In fruit production, fruit thinning is required to maximize fruit quality and to protect the mother trees. However, thinning is troublesome and laborious work. Fruit self-thinning is the spontaneous elimination of pollinated flowers or fruits within a week to a month after pollination. Since the fruit self-thinning trait has the potential to improve fruit trees, a number of studies using fruit crops such as apple, orange, and tomato have been conducted to clarify the underlying mechanisms. The Japanese pear accession ‘Chojuro’ and its descendants ‘Niitaka’, 162-29, and ‘Akiakari’ have this trait. To identify the pattern and trigger of thinning in the accessions, we pollinated all flowers on the flowering day and recorded the numbers of retained and abscised fruits and the order of flowering in the cluster. The number of retained flowers/fruits in a cluster was widely variable in ‘Chojuro’ and ‘Niitaka’, but was uniform at 3 to 6 fruits per cluster in 162-29 and ‘Akiakari’. In 162-29 and ‘Akiakari’, the earlier the flower opened, the more likely it was to be retained in the cluster, similar to previous observations in apple. In contrast, ‘Chojuro’ and ‘Niitaka’ fruits abscised independently of the flowering order. Therefore, the pattern of fruit self-thinning in pear depends on the accession. To identify the trigger for fruit self-thinning, we analyzed changes in the levels of endogenous auxins and abscisic acid. The results implicate auxin and, to a lesser extent, abscisic acid in fruit self-thinning. Retained fruits showed temperature-dependent transient auxin accumulation, which may trigger self-thinning in pear.
This study aimed to determine the optimal shoot vigor to produce large fruit and high yields of the fig (Ficus carica L.) cultivars ‘Masui Dauphine’ and ‘Houraishi’. Fruit production of the two cultivars was compared for seven years on shoots of various vigor induced by different plant densities: 20, 61, 400, 667, and 2000 trees per 1000 m2, and all shoots occupied equal-sized basal areas (0.5 m2 for each shoot). Individual shoot weight (shoot weight) and number of superfluous shoots were greater in the trees grown at higher plant density. The greater shoot growth under higher plant density was consistent for seven years for ‘Masui Dauphine’, but such an increase was suppressed after the third year for ‘Houraishi’ trees. The relationship between fruit production and shoot weight showed that fruit maturation did not last until late autumn and the number of fruits harvested (fruit number) declined on the shoots smaller than approximately 0.15 kg on ‘Masui Dauphine’ trees and by approximately 0.8 kg in ‘Houraishi’ trees. In early autumn, however, the fruit number was larger on the smaller shoots than that on the larger shoots in ‘Houraishi’ trees. The annual means of individual fruit weight (fruit weight) were negatively correlated with shoot weight from the third to seventh years for ‘Houraishi’ trees, but only for the fifth year for ‘Masui Dauphine’ trees. The fruit yield per shoot (fruit yield) was positively correlated with shoot weight based on the fruit number. However, the correlation coefficients between fruit yield and shoot weight were lower in ‘Houraishi’ trees because the fruit weight was negatively correlated with the shoot weight. Relatively large shoots in a compact tree area will be useful for ‘Masui Dauphine’ figs to avoid fruit yield decline. Conversely, smaller shoots in a large tree area will be useful for ‘Houraishi’ figs to produce more and larger fruit in early season of harvesting.
Limonoids, a group of highly oxygenated triterpenoids mostly found in the Rutaceae and Meliaceae families, have many biological and physiological activities, such as anti-cancer, anti-microbial, and insecticidal ones. Recent studies suggest that some types of limonoids bind to a bile acid receptor, TGR5 (Takeda G protein–coupled receptor 5), and confer anti-obesity and anti-hyperglycemic effects. TGR5, also known as a G protein–coupled bile acid receptor 1 (GPBAR1), is a vital member of the membrane-bound G protein–coupled receptor (GPCR) family. In this study, we revealed the content of four types of limonoids (limonin, nomilin, obacunone, and limonin glucoside) and TGR5 ligand activity in a sour orange extract. The total concentration of the four limonoids was highest in the extract of ethyl acetate, followed by methanol and hexane in sour orange seeds. On the other hand, a luciferase assay using CHO cells transfected with a TGR5 confirmed that TGR5 ligand activity in the ethyl acetate extract of the seeds was as high as that in 50 μM nomilin, followed by that in the methanol extract of the seeds. The correlation coefficient between the limonoid content and the TGR5 ligand activity showed the highest value (r = 0.867) for nomilin, which supported a previous report that the TGR5 ligand activity of nomilin is higher than that of limonin or obacunone. However, the activity of the extract could not be explained by the nomilin content alone because the nomilin concentration in the extract used for the TGR5 assay was 3.9 μM, much lower than that in the control (50 μM nomilin), suggesting unknown compounds with higher TGR5 ligand activities in the seed extracts. In addition, the extract from cotyledons or germinated seeds showed higher TGR5 activity. Taken together, these results indicate that the seeds of citrus, such as the sour orange, may be a source of compounds that prevent obesity and metabolic disorders. In a future study, it will be necessary to comprehensively investigate citrus seed extracts to identify unidentified agonists for the TGR5 receptor.
The nitrogen (N) contribution of rye (Secale cereale L.) to tomato production may increase when grown and applied with hairy vetch (Vicia villosa R.) to the soil. To examine the uptake and recovery efficiency by tomatoes and retention in the soil of N derived from 15N-labeled rye applied as a monoculture and biculture with hairy vetch, a Wagner pot examination was conducted under plastic high tunnel conditions in Sapporo, Japan. Irrespective of cover crop residue management, the peak of rye-derived N uptake occurred between 4 and 8 weeks after transplanting (WAT) and ceased between 8 and 12 WAT. Rye-derived N uptake by tomatoes (shoot + fruit) was 58.3% greater in rye monoculture treatment than in the biculture of hairy vetch and rye treatment because of higher rye-derived N input, whereas rye-derived N recovery was greater in the biculture treatment (34.0%) than in monoculture treatment (26.9%). The soil retained 47.0% and 52.5% of the rye-derived N input in the biculture (972 mg N/pot) and rye monoculture (1943 mg N/pot) treatments, respectively. Rye-derived N stored in the roots and possibly lost was estimated at 19.0% and 20.6% of the rye-derived N input in the biculture and monoculture treatments, respectively. Hairy vetch in the biculture treatment contributed 46.2% more N to tomato production than rye, and the hairy vetch N contribution was more significant during the late period (4–8 WAT) than the early period (0–4 WAT) of tomato cultivation. Therefore, the biculture may change the N release pattern from both hairy vetch and rye, with the cover crops releasing high amounts of N in both the early and late periods of tomato cultivation. These results may help improve N management in vegetable production systems by maximizing the use of plant-derived N by crops, thereby reducing N fertilizer inputs.
We investigated dry matter production and fruit characteristics of high-Brix tomatoes when plants were pinched above the third truss and electrical conductivity of the nutrient solution was gradually increased by changing the amounts of nutrients and NaCl. In the salinized treatment, fruit fresh weight was significantly decreased, and fruit Brix was significantly increased, relative to the non-salinized treatment. There were no significant differences in leaf area index, light use efficiency, light intercepted by leaves, total dry matter production, fruit dry weight, or dry matter distribution to fruit between treatments, but dry matter content of fruits was significantly increased in the salinized treatment. Therefore, dry matter production by plants was not reduced by the salinized treatment. The increase in fruit Brix was associated mainly with the increase in the dry matter content of fruits. Without reducing dry matter production, high-brix tomatoes can be produced by controlling the nutrient solution.
Begomoviruses, transmitted by whiteflies (Bemisia tabaci), have emerged as serious constraints to the cultivation of a wide variety of vegetable crops worldwide. Leaf samples from Solanaceae (tomato, tobacco, and eggplant) and Cucurbitaceae (cucumber and squash) plants exhibiting typical begomoviral yellowing and/or curling symptoms were collected in Northern Sumatra, Aceh province, Indonesia. Rolling circle amplification was conducted using DNA isolated from cucumber, squash, eggplant, and tobacco, and the full-length sequences of the begomoviruses were evaluated. The following viruses were isolated: bipartite begomoviruses Tomato leaf curl New Delhi virus (ToLCNDV), Squash leaf curl China virus (SLCCNV), Tomato yellow leaf curl Kanchanaburi virus (TYLCKaV), and a monopartite begomovirus Ageratum yellow vein virus (AYVV). Begomovirus diagnosis was conducted by PCR using begomovirus species-specific primers for Pepper yellow leaf curl Indonesia virus (PepYLCIV), Pepper yellow leaf curl Aceh virus (PepYLCAV), ToLCNDV, SLCCNV, TYLCKaV, and AYVV, which are the predominant begomoviruses. The primary begomovirus species for each plant were as follows: PepYLCAV for tomato, AYVV for tobacco, TYLCKaV for eggplant, ToLCNDV for cucumber, and SLCCNV for squash. This study provides valuable information for breeding begomovirus-resistant cultivars as horticultural crops.
We investigated dry matter (DM) and fruit production of tomato plants, the effects of CO2 levels on DM production, and light-use efficiency (LUE) in a tomato production system based on short-term, low-truss crop management during six consecutive periods over one year in a commercial greenhouse. The CO2 concentration, total dry matter production (TDM), and LUE differed significantly among the periods. Since LUE was significantly correlated with the mean daytime CO2 concentration, we modeled LUE empirically from that. We developed a model to predict LUE and DM production of tomato plants and validated the model using data from the six periods. We accurately predicted LUE and TDM within a range of ca. 400 to 650 µmol·mol−1 daytime CO2 concentration. However, when daytime CO2 concentration was beyond this range, or when a management failure such as inadequate irrigation occurred, predicted values differed significantly from observed values.
We validated a model for predicting dry matter (DM) production in growing plants without the need for destructive sampling with three tomato cultivars in a one-year experiment. In an attempt to improve DM, we managed the temperature and CO2 concentration in the greenhouse as well as the leaf area index (LAI) of the tomato plants to meet targets determined based on model predictions. In the model, leaf area and thus the intercepted light is obtained by non-destructive, manual measurements of leaf width and length and the number of leaves. Light-use efficiency is expressed as a function of daytime CO2 concentration. Although the model generally successfully predicted LAI in two of the cultivars, the observed LAI differed from the predicted value in the third cultivar. DM production, however, was predicted with high accuracy in all three cultivars from photosynthetically active radiation, temperature, CO2, and manual measurements of leaves; the predicted total DM in all cultivars at three sampling times fell within the range of observed DM ± standard deviation. By controlling temperature, daytime CO2, and LAI according to targets determined by simulations run on the model, we were able to improve yield to > 50 kg·m−2 per year. Therefore, the model was useful for improving tomato yield.
The combination effect of sowing and transplanting time on harvest time, yield, and external bulb quality was investigated to achieve earlier shipment of onions in northeastern Hokkaido, Japan. A total of five cultivars with different levels of photoperiodic responses for bulb formation were used in both the 1996/97 and 1997/98 trials. The seeds were sown on a monthly basis in a soil bed in an unheated plastic greenhouse from December to March, and the seedlings were transplanted outdoors from late April to mid-May. The daily minimum soil temperature was kept at almost 0°C, even when the air temperature in the plastic tunnel inside the greenhouse fell to −14.4°C in mid-winter. Seedling emergence took approximately 20 and 35 days in the 1996/97 and 1997/98 trials, respectively, when the seeds were sown in December and January. However, these seedlings grew slowly, and the leaf length, fresh leaf number, and leaf sheath diameter of the seedlings at transplanting time were all greater when the onion seeds were sown earlier. In addition, the bulb ripening time advanced with earlier transplanting. The cultivars, ‘Kitawase No. 3’ and ‘Kitahayate’, with an intermediate photoperiodic response, were harvested in early August if they were sown in December and January and transplanted from late April to early May. Moreover, with this combination of sowing and transplanting time, these cultivars produced an acceptable yield and bulb appearance in terms of marketable quality. The cultivar, ‘Sonic’, a typical short-day cultivar, had the earliest harvest time. However, the yield was very low due to the short period of leaf growth. On the other hand, for the cultivars ‘Okhotsk No. 1’ and ‘Kitamomiji 86’, which belong to a long-day photoperiodic response group, although the yields tended to increase under early sowing or early transplanting, they were not harvested by early August. On the basis of these observations, a new cropping type for early sowing and early transplanting will be adopted in northeastern Hokkaido by using the ‘Kitawase No. 3’ and ‘Kitahayate’ cultivars for early shipment in the domestic fresh onion market.
We aimed to monitor greenhouse tomato growth without destructive sampling and investigated an empirical growth model in which dry matter production was obtained as a product of light intercepted by plants and light-use efficiency. The intercepted light values were non-destructively determined on the basis of leaf width and length, and the number of leaves. Light-use efficiency was expressed as a function of daytime CO2 concentration. Three cultivation experiments were conducted with three tomato cultivars over two years. Significant regression lines and curves, as well as coefficients of the model, were obtained for each cultivar. Using photosynthetic curves of the three cultivars and solar radiation data, we suggest an approach to determine the recommended leaf area index to maximize dry matter production. The developed model has potential to improve yield and labor efficiency in tomato production.
In this study, we investigated the effect of salinity on photosynthesis and the distribution of photosynthates in the Japanese tomato (Solanum lycopersicum) cultivar ‘CF Momotaro York’ and the Dutch cultivar ‘Endeavour’. Although significant differences were not observed in fresh yield among the cultivars, there were significant differences between the control and salinity in terms of fresh yield, total soluble solids, and titratable acid. The total dry weight in the Japanese cultivar was not affected by salinity, but the Dutch cultivar had lower total weight under salinity compared to the control. Regarding dry mass partitioning, the Japanese cultivar had a lower dry mass ratio of vegetative organs and a higher ratio of fruits than the Dutch cultivar. Salinity did not affect the photosynthetic rate in the Japanese cultivar, but did affect the Dutch cultivar, possibly due to water use efficiency. These results indicate that this Japanese cultivar has characteristics of efficient fruit production under a low node-order pinching and high-density planting system, even under salinity conditions.
In Capsicum, loss of function mutation of acyltransferase (Pun1), putative aminotransferase (pAMT), putative ketoacyl-ACP reductase (CaKR1), and R2R3-MYB transcription factor (CaMYB31) have been reported to be the genetic causes of non-pungency. In the present study, 245 C. chinense accessions were initially screened for non-pungency attributes. Six candidates with identification numbers, No. 3327, No. 3356, No. 3529, No. 4026, No. 4028, and No. 4034 were selected by tasting test, and the non-pungency attribute was confirmed by high-performance liquid chromatographic analysis. Expression and sequence analysis inferred that the non-pungency of No. 3529 was due to the non-expression of Pun1. Analysis of pAMT confirmed that No. 3356 (pamt5) and No. 4034 (pamt9) had loss of function mutations. Because the non-pungency of No. 3327, No. 4026, and No. 4028 did not seem to be caused by mutation of either Pun1 or pAMT, the CaKR1 mutation was further examined using a polymerase chain reaction-based, co-dominant marker. Genotyping clarified that No. 3327, No. 4026, and No. 4028 had the same mutated CaKR1 allele as non-pungent No. 3341. Moreover, a crossing test with a pungent Habanero and No. 3341 clearly revealed that the non-pungency in No. 3327, No. 4026, and No. 4028 was a result of a loss of function mutation of CaKR1. Our previous and present studies have shown that non-pungent cultivars of C. chinense possessing pamt are widely distributed in Central America, South America and the West Indies (Caribbean), while non-pungent cultivars possessing Cakr1 originate from Bolivia and Peru. Some artificial selection may have occurred that was based on a preference for non-pungent peppers in the local region of origin.
Paphiopedilum niveum (Rchb.f.) Stein, an endangered species, has been listed in CITES Appendix I and its germplasm conservation is required. To improve the regeneration of cryopreserved somatic embryos (SEs), adding 0.1 mM ascorbic acid (AsA) at a critical step during cryopreservation was investigated. The reactive oxygen species (ROS) and malondialdehyde (MDA) contents were also assessed during five steps (preconditioning, 1st preculture, 2nd preculture, osmoprotection, and dehydration) of a developed V cryo-plate technique as described briefly. Two-month-old SEs were preconditioned on modified Vacin and Went medium (MVW) containing 0.1 M sucrose for seven days. These SEs were precultured on MVW containing 0.2 M sucrose for one day (1st preculture) before being transferred to the same medium with 0.6 M sucrose for one day (2nd preculture). Precultured SEs were embedded on a cryo-plate, incubated in loading solution (LS) with 1.2 M sucrose for 30 min at 25°C and dehydrated with plant vitrification solution 2 (PVS2) for 60 min at 25°C. It was found that applying AsA on day 7 after culture (before the 1st preculture) could reduce total ROS and MDA levels, leading to a high regeneration percentage (39%) of cryopreserved P. niveum SEs.
Fusarium root rot of lisianthus (Eustoma grandiflorum) caused by Fusarium solani is one of the most important and damaging lisianthus diseases. It occurs commonly in Japan and worldwide and causes serious crop losses. However, little effort has been made to breed lisianthus for resistance to this disease. We initiated a breeding program for resistance to F. solani in 2014. Twenty-nine lisianthus cultivars (E. grandiflorum) and one inbred line of Eustoma exaltatum were evaluated for resistance to two isolates (MAFF712388 and MAFF712411) of F. solani, as a first step toward the breeding of resistant cultivars. Seedlings were inoculated following injury by needle, then grown using hydroponic equipment—an efficient and reliable method for evaluating resistance. We found large differences in resistance among the 29 cultivars and the one inbred line tested. ‘Papillon Pink Flash’ was highly resistant to both isolates and showed no disease symptoms in a total of four tests. Furthermore, E. exaltatum Ohkawa No. 1 was highly resistant to isolate MAFF712388, showing no disease symptoms, and resistant to isolate MAFF712411. On the other hand, ‘Mink’, ‘Nagisa A’, ‘Nagisa B’, and ‘Vulcan Marine’ were stably susceptible with 70% to 100% of plants of these four cultivars wilting in all tests. MAFF712411 had greater pathogenicity than MAFF712388, but it is not clear whether the two isolates belong to different races.
We investigated the molecular mechanisms underlying the pigmentation patterns of the dorsal petals in torenia (Torenia fournieri Lind. ex Fourn.) cultivars. ‘Piccolo Mix’ consists of lines exhibiting different pigmentation patterns in the limb of the dorsal petal, i.e., entirely pigmented (all-pigmented line), picotee with a pigmented margin (half-pigmented line), and entirely pale (pale line). In the all- and half-pigmented lines, expression of T. fournieri CYCLOIDEA2 (TfCYC2), which is involved in dorsal–ventral floral asymmetry, was inhibited by integration of Ty1/Copia-like LTR retrotransposon TORE2 into the exon of TfCYC2 (TfCYC2TORE2). The all-pigmented line was homozygotic for TfCYC2TORE2, while the pale line was homozygotic normal-type TfCYC2 (TfCYC2+). The half-pigmented line was heterozygotic TfCYC2TORE2/TfCYC2+. Therefore, the extent of pigmentation of the dorsal petal is negatively correlated with the gene dosage of TfCYC2+. Further, ‘Crown Violet’, another torenia cultivar exhibiting the same pigmentation pattern as the all-pigmented line of ‘Piccolo Mix’, was also homozygotic for TfCYC2TORE2. These results indicate that TfCYC2TORE2 is responsible for the marked enrichment of flower pigmentation patterns seen in torenia cultivars.
Typically, hydrangea (Hydrangea spp.) plants produce flowers from early to mid-summer. However, their basal shoots often continue to produce flowers from late summer to autumn, and we call this unseasonal flowering. The flowering frequencies and flowering period durations of basal shoots were studied using 23 hydrangea cultivars and lines in 2017, 2018, and 2019. The flowering frequencies of basal shoots were relatively high in ‘Christmas’, ‘Endless Summer’, ‘Ezo’, ‘Rosea’, and ‘Sumida-no-hanabi’ in each year of the study. The flowering period durations of basal shoots ranged from one to six months among the cultivars and lines studied. Basal shoots of ‘Endless Summer’ and ‘Rosea’ continuously flowered during each year of the study period. The basal shoots of ‘Hatsushimo’, ‘Jyogasaki’, ‘Maihime’, ‘Masja’, ‘Ms. Hepburn’, ‘Uzu’, and No. 5 never flowered after August in any of the study years. Using ‘Masja’ and ‘Rosea’, axillary buds expected to develop into basal shoots were studied for flower bud initiation in November 2018. Flower bud initiation was observed in 8.9% and 77.4% of axillary buds of ‘Masja’ and ‘Rosea’, respectively. The number of nodes produced before flower bud initiation in the buds ranged from 10 to 12 and 8 to 13 in ‘Masja’ and ‘Rosea’, respectively. The numbers of nodes corresponded to those of the basal shoots that flowered up to August 2019 in both cultivars. The number of nodes produced by basal shoots of ‘Rosea’ that flowered after August 2019 ranged from 14 to 19, which was higher than those observed for the axillary buds expected to develop into basal shoots in November 2018. In conclusion, the flowering period duration of hydrangea basal shoots differs among cultivars. The floral initiations on the apical buds of the basal shoots after the previous autumn largely contribute to unseasonal flowering occurrences after August in hydrangea.
This study investigated the antifungal effect of chlorine dioxide (ClO2) dipping on Botrytis cinerea, the causal agent of gray mold, on cut rose flowers (Rosa hybrida L.). In vitro, the spore germination of gray mold was inhibited 100% by instant dipping with ClO2 solution (5 to 10 μL·L−1). In particular, ClO2 at 5 μL·L−1 was found to be ideal for hindering spore activity without causing any damage to the petals. This ClO2 antifungal effect on cut flowers was investigated in a white cultivar ‘Beast’ with different treatments: dipping (one second), spraying (4.8 mL), or gassing (two hours) with 5 μL·L−1 ClO2. Six days after ClO2 treatment, the incidence of gray mold in the artificially-inoculated flowers was 2.5% (dipping), 9.4% (spraying), or 8.4% (gassing), respectively, which were all significantly lower than the control incidence of 17.6%. Especially, ClO2 dipping reduced the incidence of gray mold by up to 26.1% compared to the control in five other rose cultivars (‘Antique Curl’, ‘Green Beauty’, ‘Feel Lip’, ‘Pink Heart’, and ‘Venus Berry’). No petal discoloration was detected, and petal color values (chroma or hue) were maintained regardless of ClO2 dipping. This result suggests that immediate ClO2 dipping is applicable to inhibit gray mold on cut rose flowers at a level of 5 μL·L−1 just before postharvest storage.