On the cover

Broccoli production and consumption in Japan have been increasing annually, with the crop set to receive “designated vegetable” status by 2026. Domestically produced broccoli is primarily shipped for fresh retail markets, with strict shipping standards prioritize a head diameter of 12 cm. Typically, only one head per plant meets this standard; however, new cultivation techniques called “L-shaping” and “V-shaping” now allow for the harvest of two or more heads from a single plant. In processing and food service sectors, inexpensive imported products are commonly used, however, there is growing interest in domestic alternatives. Focusing on the fact that disassembled florets are used for processing, a “large head production system” that is not constrained by conventional shipping standards has been developed and its adaptability has now been confirmed nationwide. Furthermore, since higher head positions are expected to reduce labor during harvest, changes in stem length in response to planting density have also been elucidated.

(Provided by M. Takahashi: Institute of Vegetable and Floriculture Science, NARO)

Climate change has affected fruit tree production because meteorological environments determine annual yield, quality, and suitable cultivation locations. This review focuses on the physiological and physical effects of each meteorological element on fruit trees, the impact of climate change on fruit production, and adaptation strategies. The most critical role of temperature is the temporal control of developmental stage changes via developmental rate regulation. Extremely high and low temperatures can cause necrosis of fruit tree tissue, which is a physical effect of heating or freezing. Solar radiation and soil moisture drive quantitative control to determine the size and weight of the entire plant or each part of the fruit tree via photosynthesis. Climate change affects fruit trees through high temperatures and water stress. Temperature rise has altered the development of fruit trees, resulting in earlier flowering, delayed fruit coloration, changes in fruit quality, and increased risk of peel and flesh disorders. Warmer temperatures in autumn and winter delay the release from endodormancy and hardening, as well as accelerating de-hardening, resulting in freezing injuries and flowering disorders. Sunny days with extremely high temperatures cause physical damage to tissues, resulting in sunburn. Water stress reduces the photosynthesis rate, resulting in reduced fruit growth. A lot of research has been conducted on the development of adaptive measures. Adaptation strategies for fruit tree production can be divided into three stages. In Stage 1, short-term adaptation strategies focusing on production techniques include the use of shading materials or reflective films, regulation of development using greenhouses or plant growth regulators, girdling, or shifting the nitrogen fertilization period. Stage 2 involves the use of cultivars that are better adapted to climate change and is a medium-term adaptation strategy because it requires replanting. Stage 3, species or area conversion, is a long-term adaptation strategy. It refers to cultivating fruit tree species that have not been traditionally cultivated in the area or the relocation of cultivation areas. To support this strategy, maps showing future locations suitable for several species have been developed.

Tropical fruits, including bananas (Musa accuminata Colla), pineapples (Ananas comosus (L.) Merr.), and mango (Mangifera indica L.), are important edible fruits worldwide. The breeding of tropical fruit tree species poses many challenges compared with the breeding of annual crops because of their long juvenile period and the high cost of raising individuals to maturity in the field. With progress in next-generation sequencing (NGS) technologies, genome sequencing and identification of trait-associated loci have greatly progressed in recent years. The whole-genome sequences of most of the major tropical fruit tree species have been reported. Recent high-accuracy long-read sequencing technologies have enabled telomere-to-telomere and haplotype-resolved genome sequencing. These technologies have also been adopted for the genome sequencing of tropical fruit tree species. Quantitative trait locus (QTL) mapping and genome-wide association studies based on NGS technologies have been conducted on tropical fruit tree species to detect trait-associated loci. These analyses helped identify multiple QTLs that may contribute to efficient breeding selection. Two issues have been raised when applying QTL information to breeding selection in pineapple programs in Japan. The first is the adaptability of various populations, for which developing haplotype-resolved QTL information has been proposed as a solution. The second is to consider multiple QTLs among multiple traits in DNA-based selection. To utilize multiple QTLs among multiple traits for DNA-based breeding selection, a scheme for accumulating preferred alleles has been proposed and applied to pineapple breeding programs in Japan.

Broccoli (Brassica oleracea L. var. italica) production and consumption have rapidly increased in Japan, and it is expected to be recognized as a “designated vegetable” by 2026. However, approximately 30% of domestic broccoli for consumption is imported, which means that there is a pressing need to increase domestic production. In Japan, broccoli heads that are harvested and shipped to the market are primarily from the apical bud, with only one head per plant. If the lateral heads from lateral branches (axillary buds) could grow to a marketable size, broccoli production would significantly increase. This study aimed to develop cultivation methods that enable harvesting two heads per plant using lateral branches. By selecting cultivars, investigating the probability of axillary bud generation at each node, and determining the proper timing for decapitation, two cultivation methods were established: “L-shaping” and “V-shaping”. L-shaping is a method that enables the harvest of 10 cm diameter lateral heads after the harvest of a 12 cm diameter apical head in April and May by limiting the number of lateral branches to one or two. This method increased the number of 10 cm heads by approximately 80%, with total yields reaching 17,000 kg per ha. V-shaping enables the harvesting of two 12 cm diameter heads during autumn cropping by pinching the apical bud and limiting the number of lateral branches to two. Pinching at the 7^th to 11^th leaf stage increased the number of 12 cm heads by approximately 60%, with yields reaching 13,000 kg per ha. Both methods exceeded the national average yield of 10,000 kg per ha, making them highly promising for increasing fresh broccoli production in Japan.

Production and consumption of broccoli in Japan are gradually increasing; however, the country is highly dependent on imports to meet the growing demand. Large head production systems with ‘Grandome’ can decrease the reliance on imports, but their adaptability across broader areas remains unclear and it is also necessary to consider other cultivars according to regional and cultivation conditions. Therefore, in this study, ‘Grandome’ yield was evaluated from 2019 to 2021 at six autumn to spring production sites (Hyogo, Hiroshima, Kumamoto, Kanagawa, Kagawa, and Ehime). In addition to the yield evaluation of ‘Grandome’, cultivar selection tests suitable for large head production were conducted at the former three sites using 25 cultivars in Experiments 1 to 3, while the yield evaluation exclusively for ‘Grandome’ was conducted under different fertilization conditions and planting densities at the latter three sites in Exp. 4, comparing floret yield (small pieces of broccoli separated from the head). Experiments 1 to 3 revealed that ‘SK9-099’ produced high yield during the relatively warm November harvest, whereas in the subsequent December–January harvest, ‘Grandome’ and ‘Clear’ produced high yields. In years that were colder than usual during the aforementioned period and for cropping types with a harvest period from February to March through a severe cold season, late-maturing cultivars, such as ‘Tomoe’ and ‘Konbanwa’, produced high yields due to their strong low-temperature enlargement capacity. Among cropping types with a harvest period from April to May, ‘Grandome’ produced a high yield. Moreover, these cultivars could be grown in converted paddy fields. In Exp. 4, high fertilization rates and wide planting promoted head enlargement. Wide planting increased the yields under simultaneous harvesting. However, under selective harvesting, where enlarged heads were individually harvested, head size was comparable between the standard and wide planting. Therefore, wide planting had no yield-increasing effect. The optimal planting density and harvest size for maximizing yield remain unclear. Nevertheless, for the first time, this study showed that the effect of planting density on yield varied based on the harvesting method. This study achieved a floret yield of 20,000 kg per ha across all six locations in nine cultivation trials in Japan, highlighting the broad adaptability of large head production systems, particularly in the autumn to spring production areas in Japan.

Large head production systems, mainly for autumn, winter, and spring cropping, have been examined to reduce the cost of broccoli production for processing. To ensure year-round supply, the adaptability of this system in regions with summer cropping should be evaluated. Therefore, in this study, we selected cultivars suitable for producing large heads and examined the effects of harvest size, fertilizer, plant spacing, and mulching on their growth and yield in Shiojiri City, Nagano Prefecture, which is a summer cropping region for broccoli. Spring-sown cropping (harvested from June to July) and summer-sown cropping (harvested from September to November) were investigated from 2019 to 2022. Broccoli heads were enlarged even at a conventional plant spacing of 37.5 cm (planting density: 59,260 plants per ha), and mulching advanced the harvest period. However, effect of fertilizer on yield was relatively small. Among the 23 cultivars tested, ‘SK9-099’ was found to be the most suitable. The average temperature during cultivation should be below 18°C for spring-sown crops and below 22°C for summer-sown crops for best growth. Moreover, harvesting heads 20 cm in diameter yielded up to 35,000 kg per ha of florets. However, the risk of yellowing increased with increasing size; therefore, the practical harvest size should be approximately 16 cm in diameter (20,000 kg per ha), which yielded approximately three times the national average yield of 6,000–7,000 kg per ha. We also analyzed the temperature changes during transportation using different packaging methods; Styrofoam boxes with ice (SB) and two types of functional films: Pal Fresh (PF) and Xtend (XT) and investigated the quality retention period after arrival at different states (head or florets). SB transport consistently maintained the quality for over 14 days, even for larger sizes, but film packaging showed instability in terms of its cooling effect during transport, with mold observed upon arrival in some cases. Moreover, transport and storage of florets can cause serious problems, such as browning at the cut edges, making them impractical for commercial use.

The demand for broccoli (Brassica oleracea L. var. italica) in Japan is increasing, driven by both the fresh market and processing industries. In this study, we attempted to clarify the influence of plant density on broccoli stem elongation in autumn–winter cropping because longer stem lengths and higher head positions have the potential to reduce the labor costs associated with harvesting and thereby increase broccoli production. We set up plant density treatments with approximately 2000, 3000, 4000, 5000, and 6000 plants·10 a⁻¹ (expressed as 2000D, 3000D, etc., hereafter) and measured the stem lengths of two cultivars, ‘Pixel’ and ‘Grandome’ (from the ground surface to the apical bud) over time. Significant differences were observed among the treatments after approximately 800°C of accumulated temperature (AT), which coincided with the onset of leaf overlap among adjacent plants in 6000D. At approximately 1250°C of AT, the stem lengths of ‘Pixel’ under 4000–6000D showed increases compared to those under 2000D and 3000D in response to the accumulation of solar radiation (ASR). Additionally, the vegetation coverages in 2000D and 3000D were 62% and 85%, respectively, indicating room for increase, whereas those in 4000–6000D almost reached their saturation level of over 94%. Further, stem length under 6000D was 11–15% higher than that under 2000D, suggesting that the stem elongation observed in dense planting was due to a shade avoidance response caused by mutual shading. As the plant density decreased, the proportion of branches and leaves increased in ‘Pixel’ and ‘Grandome’, respectively, indicating that the parts that developed under favorable light conditions differed among cultivars. The number of harvested heads decreased as plant density decreased, but there were no significant differences in yield among plant densities in ‘Grandome’. However, the yield of ‘Pixel’ was significantly lower in the lowest plant density (2000D) than in moderate conditions (4000D). In conclusion, there was no restriction on plant density from the perspective of yield, especially for the cultivar ‘Grandome’, which produces a large head, and the density could be adjusted within a range of 2000–6000D to achieve the desired stem length and head size.

The rising demand for strawberries in tropical and subtropical regions underscores the need for effective cultivation techniques. However, the challenges posed by high temperatures in these areas have hindered successful strawberry cultivation. In this study, we investigated the impact of nighttime light-emitting diode (LED) supplemental lighting on the growth, yield, and fruit quality of three everbearing strawberry cultivars, ‘Koi-ichigo’, ‘KS33’, and ‘KS38’. They were cultivated in a controlled environment greenhouse with a crown and growth medium cooling system from August to December 2023 under high temperatures similar to tropical regions. LED lights were employed daily for 3.5–5.5 hours post-sunset to extend the day length to 16 hours per day. Under daily mean air temperatures exceeding 26°C until October, ‘Koi-ichigo’ under a natural day length underwent anthesis later than the other two cultivars. In the LED treatment, flower bud differentiation was stabilized in all cultivars due to increased photosynthetic photon flux density (PPFD). All three cultivars exhibited enhanced growth and yield under the LED treatment. Furthermore, the cultivars’ total shoot dry weight increased in response to LED supplementation. Although the LED treatment increased the number of harvested fruits, the fruit weight and soluble solid content remained comparable to those in the control. The leaf area index decreased in the LED treatment in ‘Koi-ichigo’ and ‘KS33’. At the same time, no difference in light-use efficiency was found between the control and LED treatment, and cumulative light interception surpassed that of the control in the LED treatment in all cultivars. These findings suggest that when growing everbearing strawberry cultivars in tropical and subtropical regions, nighttime LED supplemental lighting effectively stabilizes flower bud differentiation and increases the total shoot dry weight due to increased cumulative light interception, resulting in increased yield.

The onion (Allium cepa) is a biennial plant, and development and size of the bulb are important factors in determining its productivity. During onion cultivation, premature flowering during crop growth, also known as bolting, must be avoided because it negatively affects bulb development and impairs quality. In many plants, day length and temperature are related to flowering, and the FLOWERING LOCUS T (FT) gene regulates flower bud differentiation at the genetic level. Onion flowering is promoted by vernalization and is correlated with upregulation of AcFT2, which may be a key signal for flowering in vernalized meristems. No studies on AcFT2 expression or its relationship with bolting under field conditions have been conducted; therefore, we investigated these points in field-grown onions under autumn-sowing (overwinter) cultivation. In this study, we revealed that relatively late-maturing cultivars for spring-sowing cultivation are not suitable for autumn-sowing cultivation due to their high bolting incidence. Based on these results, AcFT2 expression in the leaf blades of relatively late-maturing cultivars under spring-sowing cultivation was analyzed during plant growth under autumn-sowing cultivation. Our results indicated that AcFT2 expression in late-maturing cultivars gradually increases during plant growth and peaks before visible bolting occurs. This suggests that monitoring AcFT2 expression may serve as an early indicator of bolting risk in late-maturing cultivars. We also investigated the effect of seedling size at transplantation and the expression of AcFT2 and found that seedling size at transplantation affected the incidence of bolting, with higher expression of AcFT2 in large seedlings that are more susceptible to bolting.

Although the fragrant wild cyclamen, Cyclamen purpurascens, is widely used as a parent plant for breeding of fragrant cyclamen cultivars, the color variety of fragrant cyclamen is limited. To develop cultivars with a wider range of flower colors, it is crucial to understand the flavonoid biosynthetic pathway involved in flower color in C. purpurascens as a crossbreeding parent. In this study, we isolated the gene (CpurF3H) encoding flavanone 3-hydroxylase, a key enzyme in determining flower color in cyclamen, from C. purpurascens for the first time and investigated its expression and function. The full-length cDNA sequence of CpurF3H obtained from young petals contained a 1,113-bp open reading frame (ORF) encoding 371 amino acids, showing 82.1–88.0% amino acid sequence identity with F3Hs from other plant species. The expression analysis showed that CpurF3H is strongly expressed in young petals, but rapidly decreases in petals following anthesis, suggesting that it functions during the early stages of flower development. Next, in vitro assays showed that recombinant CpurF3H proteins can convert naringenin to dihydrokaempferol. In addition, a complementation assay using the Arabidopsis thaliana f3h mutant confirmed the accumulation of anthocyanins in CpurF3H-transformed plant. Overall, these results strongly suggest that CpurF3H participates in flavonoid biosynthesis and flower coloration in C. purpurascens.

Evergreen azalea cultivars are used as ornamental shrubs and pot plants not only in Japan, but also in Western countries. These cultivars were developed from wild species native to Japan, and through selection and crossing, cultivar groups such as the Ryūkyū-tsutsuji, Hirado-tsutsuji, Edo-kirishima, Satsuki and pot azalea have been developed. In this study, we focused on the genetic contribution of wild species to the development of evergreen cultivars and used microsatellite loci to examine the genetic involvement of wild species, particularly Rhododendron ripense. The utilization of seven microsatellite loci enabled cultivar identification and an estimation of bud mutation lines. The results of STRUCTURE analysis revealed that the R. ripense cluster was predominant in large-flowered cultivars such as Kishi-tsutsuji, Ryūkyū-tsutsuji, and Ōkirishima. The involvement of the R. ripense cluster was also observed in pot azalea developed in Western countries. Additionally, the genetic involvement of R. scabrum was confirmed in many cultivars of Ōkirishima and Hirado-tsutsuji. Regarding small-flowered cultivars, the Yama-tsutsuji and Kurume-tsutsuji cultivar groups were dominated by the R. kaempferi cluster, while the Satsuki cultivar group was dominated by the cluster containing R. indicum, R. eriocarpum, and others. These results enable us to reevaluate the classification of azalea cultivars by conducting a more detailed study of cultivar groups composed of the same clusters.

Fittonia albivenis (Lindl. ex Veitch) is a popular ornamental plant because of its dark green leaf blades and white, pink or red veins. This study aimed to anlayze the difference between red vein leaves and white vein leaves. By HPLC analysis, pelargonidin was detected from all red-vein cultivars, while no anthocyanins were detected from all white-vein cultivars, indicating vein pigmentation is due to the presence or absence of anthocyanin. Interestingly, white-vein cultivars were classified into two types: one type accumulated flavone in leaves (‘White Star’, ‘Snow Anne’, and ‘White Tiger’), and the other type did not accumulate any flavonoids in leaves (‘Sunny Green’ and ‘Sunny Yellow’). The flavone-accumulating ‘White Star’ did not show any major difference in anthocyanin biosynthetic gene expression compared to red-vein cultivars, but did have a stop codon mutation in anthocyanidin synthase (ANS). ANS cDNA of ‘White Star’ and ‘Snow Anne’ had a premature stop codon at 290^th bp, and ANS cDNA of ‘White Tiger’ had a premature stop codon at 943^rd bp due to an A-insertion at 790^th bp, resulting in a truncated ANS protein. On the other hand, a flavonoid-less cultivar, ‘Sunny Green’, showed lower expression levels of anthocyanin biosynthetic genes than red-vein cultivars, especially for chalcone synthase 1 (CHS1), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), and dihydroflavonol 4-reductase (DFR). The expression level of flavone synthase (FNS) was not significantly different from red-vein cultivars and cDNA of FNS appeared to encode full-length protein, indicating the anthocyanin-less and flavone-less phenotype is due to CHS1, CHS2 or CHI steps. As for CHS2, ‘Sunny Green’ expressed intron-inserted CHS2 resulting in a truncated protein; however, this transcript was detected from other cultivars. From these results, it was suggested that low expression of CHS1 and CHI was important for flavonoid-less leaves in ‘Sunny Green’. In addition, ‘Sunny Green’ did not express full-length F3H transcripts. Therefore, multiple independent mutations in anthocyanin biosynthetic genes contribute to anthocyanin-less leaves in fittonia.

In vitro culture is essential for propagating F₁ cultivar parents and vegetatively propagated gentian cultivars. In vitro overwintering bud (OWB) formation is also crucial to maintain and propagate these plants. This study examined the effects of temperature, medium composition, and photoperiod on in vitro growth, including OWB formation, using Gentiana triflora and G. scabra as model species in leaf cultures, a practical propagation method. The growth parameters of the G. triflora line TY1-11-4-9 were assessed under different temperature and sugar composition conditions, revealing positive and negative correlations between OWB and rosette-shaped shoot (RSS) formation and between OWB and flower bud formation, respectively. Consequently, further investigations focused on these growth parameters. Temperature effects on four cultivars/lines revealed interspecific differences: at all temperatures, G. triflora had a higher rate of flower bud formation than G. scabra, whereas G. scabra showed increased OWB and RSS formation. Culturing under low temperature (15°C/15°C: regeneration stage/OWB induction stage, which was also applicable below) conditions, which may be impractical owing to slow growth effects, suppressed flower bud formation in G. triflora, but promoted RSS and OWB formation. Similar effects, albeit milder, were observed at 20°C/15°C, and these conditions were further explored as a practical method combined with other treatments to induce OWB formation. The medium sugar composition had negligible effects on in vitro growth, whereas gibberellin at 1.0 mg·L⁻¹ in the medium composition suppressed OWB and RSS formation in G. scabra. Photoperiod variations affected several growth parameters, with a 12-h photoperiod promoting a high rate of OWB formation in the G. triflora line TY1-11-4-9. In conclusion, low-temperature treatments after a certain amount of growth, along with combined treatments such as photoperiod adjustments and gibberellin inhibitor administration, show promise for promoting OWB formation in gentians. Furthermore, the interspecific differences observed in flower bud formation, RSS production, and OWB formation contribute to a better understanding of gentian physiology and genetics.

In ‘Fuyu’ persimmons (Diospyros kaki Thunb.), crunchiness is a preferred postharvest attribute among both distributors and consumers. The present study first examined softening characteristics during storage at 0, 5, 10, 15, 20, and 25°C. Fruit stored at 0°C remained firm for 84 d, while that stored at 5°C had a 100% softening rate within 35 d. At 10 and 15°C, over 70% of fruit softened within 49 d and 63 d, respectively. The softening rate was relatively slower at 20 and 25°C, with only 27% softened fruit after 56 d at 25°C. The potential of a newly developed sugar-ester (SE) edible coating to delay fruit softening and maintain postharvest quality was then assessed during storage at 0 and 25°C. Uncoated fruit stored at 0°C for 56 d developed chilling injury (CI) symptoms (rapid fruit softening and peel browning) within 2 d of rewarming at 20°C. These CI symptoms were notably mitigated in SE-coated fruit. At 25°C, SE coating also delayed fruit softening and peel color change in addition to reducing fruit shrinkage. In conclusion, in ‘Fuyu’ persimmons ambient temperature (20–25°C) storage in combination with an edible SE coating is recommended for the high demand Christmas and new year seasons and 0°C storage with an edible SE coating is suitable for longer storage and distribution.