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Tomatoes (Solanum lycopersicum) are one of the most important vegetable crops worldwide, but domestication has greatly reduced their genetic diversity. Their wild relatives, such as Solanum pennellii, harbor traits valuable for improving fruit quality, yield, and stress tolerance. Introgression lines (ILs), developed from crosses between the cultivar ‘M82’ and S. pennellii accession LA716, serve as powerful genetic resources for dissecting quantitative trait loci (QTLs) underlying complex traits. This review highlights key IL-based studies focusing on fruit development and quality. IL5-4 and IL8-3 exhibit elevated Brix values compared with ‘M82’, making them useful models for studying sugar accumulation and blossom-end rot, a serious physiological disorder in tomato. IL12-1-1 produces substantially larger fruits due to enhanced cell division and hormonal regulation during early development, and candidate genes for these traits have been identified in its introgressed region. By integrating genetic and physiological insights from ILs, researchers have uncovered fundamental mechanisms underlying fruit traits. These findings deepen our understanding of tomato biology and provide valuable resources for future breeding programs aimed at improving fruit quality and resilience.

(Provided by H. Ikeda: Utsunomiya University)

Tomatoes, Solanum lycopersicum, are globally important crops, valued for their nutritional, economic, and scientific importance. However, domestication has narrowed their genetic diversity, limiting advancements in key traits, such as yield, quality, and stress resistance. Their wild relatives, such as Solanum pennellii, are vital genetic resources, harboring traits for enhanced fruit size, sugar accumulation, and stress tolerance. S. pennellii-derived introgression lines (ILs), developed by crossing the S. lycopersicum cultivar ‘M82’ with S. pennellii accession LA716, have been instrumental in dissecting complex traits controlled by quantitative trait loci (QTLs). This review highlights key IL-based studies on fruit development and quality, focusing on IL5-4, IL8-3, and IL12-1-1. IL5-4, harboring a chromosomal segment from S. pennellii when introgressed into chromosome 5 of S. lycopersicum, exhibits elevated Brix values because of enhanced vegetative biomass. IL8-3, which carries a chromosomal segment from S. pennellii when introgressed into chromosome 8 of S. lycopersicum, also demonstrates high Brix values, which is linked to the increased expression of cell wall invertase and sucrose synthase during fruit ripening. Additionally, IL5-4 and IL8-3 differ from ‘M82’ in their susceptibility to blossom-end rot (BER), a serious physiological disorder in tomatoes, making them valuable resources for investigating the mechanisms underlying the incidence of BER. IL12-1-1, a derivative of IL12-1, produces substantially larger fruits with higher mean weights and sizes, attributed to the increased cell division and elevated levels of auxin and cytokinin during early development. Candidate genes, including Solyc12g005250 and Solyc12g005310, within the chromosomal region of S. pennellii in IL12-1-1, have been proposed to contribute to these traits. In recent years, the use of advanced methods, such as genome-wide association studies (GWASs), has facilitated QTL identification. However, GWASs require comprehensive phenotypic data and analyses of diverse accessions, which are hindered by low genomic diversity in cultivated tomatoes. Conversely, IL-based QTL analysis remains a robust approach for uncovering genetic mechanisms and advancing tomato breeding programs.

Dahlia (Dahlia variabilis) is a popular ornamental plant belonging to the Asteraceae family grown in many countries because of its wide variation in flower shape, size and color. Among its diverse attractive traits, flower color is one of the most important ornamental traits in dahlia. The pigments in dahlia flowers are flavonoids (anthocyanins, flavones, and 6′-deoxychalcones), and the presence and amount of these pigments determines the color of the flower. In this review, the history of research on dahlia flower color, biosynthesis of floral pigments focusing on anthocyanin biosynthesis, 6′-deoxychalcone biosynthesis and bicolor pattern formation, as well as unstable pigmentation in bicolor cultivars, are summarized. Finally, for future dahlia breeding, candidate genes determining flower colors are proposed.

The long-term preservation of pollen is imperative for the conservation of genetic resources and cross-breeding. In the present study, we demonstrated that preserved pollen of the Japanese pear (Pyrus pyrifolia (Burm. f.) Nakai) retains viability for a minimum of 50 years. In 1973, fresh pollen from ‘Chojuro’ was collected and immediately subjected to freeze-drying for 15 minutes at pressures ranging from 3.3 to 13 Pa. The pollen was then sealed in ampules under a vacuum and preserved at −20°C for 40 years followed by −30°C for 10 years. In 2013 and 2023, the viability of this pollen was investigated. The rate of pollen germination showed no significant differences between the preserved and fresh pollen. In 2013, flowers of ‘Kosui’ and ‘Niitaka’ were pollinated with pollen preserved for 40 years as well as fresh pollen. The growth of the pollen tubes in the pistils of preserved pollen was normal. Pollination with preserved pollen resulted in 77.1 and 86.7% fruit set, yielding 3.2 and 8.3 perfect seeds per fruit in ‘Kosui’ and ‘Niitaka’, respectively. In 2023, the fruit set and perfect seeds per fruit of ‘Kosui’ pollinated with 50-year-preserved pollen were 66.7% and 3.5, respectively. There were no significant differences between preserved and fresh either year for either trait. The results of the present study demonstrate that the viability of pear pollen can be sustained for a minimum of 50 years when preserved in a freeze-dried state at temperatures ranging from −20 to −30°C.

Marker-assisted selection (MAS) using DNA markers linked to a single or a few quantitative trait loci (QTL) with low genetic contribution has not been effectively and practically applied due to the significant loss of target offspring. High sugar content (soluble solids content, SSC) is an important breeding goal for fresh pineapple in Japan. We investigated the efficiency of MAS performed before primary phenotypic selection for a first-fruited F₁ pineapple population of ‘Yugafu’ × ‘Yonekura’ for a single QTL with 11.6% genetic contribution controlling SSC. Four genotypes at this QTL were detected by a SNP marker and segregated 1:1:1:1. Statistical analysis was performed using logSSC values. The logSSC means in the four genotypes were significantly separated, the distributions within each genotype were close to normal distribution, and the variances within genotypes were not significantly different. The target offspring (> 17 Brix%) in this population was estimated to be 5.3%. Among four genotypes in the QTL, MAS of selecting the genotype with the highest mean SSC and MAS of selecting the top two genotypes for mean SSC were called 25% MAS and 50% MAS, respectively. Selection efficiency (Se) was defined as the ratio of the target offspring selected by MAS to the target offspring present in the initial population before MAS. Se was 0.51 and 0.81 for 25% and 50% MAS, respectively, resulting in a loss of 49% and 19% of the target offspring. To compensate for this loss and obtain the same number of target offspring achieved by conventional phenotypic selection without MAS, the initial population needed to be increased by ×(1/Se), which was defined as the effective MAS scale (EMSS). The EMSS was 1.95 and 1.24 for 25% MAS and 50% MAS, respectively, and the population sizes after MAS were 0.49 and 0.62 times the population without MAS, respectively, indicating a small difference between the 25% and 50% MAS. Considering this result and the cost of MAS, 50% MAS was recommended over 25% MAS for the population. These results showed that efficient MAS without reducing the number of target offspring was achievable by expanding the initial population size by EMSS.

We developed a “synchronized germination system” for large-scale transformation of a model tomato cultivar, ‘Micro-Tom’, and used it to generate large quantities of uniform explants for transformation. Following initial germination inhibition in a medium with high concentrations of sugar and other compounds, over 80% of the selected seeds germinated synchronously after being transferred to a germination-induction medium (GI medium). In addition, we used the “synchronized germination system” to investigate the appropriate cotyledon age and selection agent for efficient transformation. To study the effect of cotyledon developmental stages on transformation, ‘Micro-Tom’ seeds were treated with the “synchronized germination system”. Cotyledons cultured for 1, 2, 4, and 6 days in GI medium were transformed using Agrobacterium-pCAMBIA1305.1 for β-glucuronidase (GUS) reporter expression. The results showed a significantly higher GUS-positive shoot formation rate for cotyledons cultured for 2 days compared to those cultured for 4–6 days. Furthermore, using GUS and the anthocyanin regulatory gene VlmybA1-2 as reporters, the effects of kanamycin, hygromycin, and G-418 on shoot selection were compared using 2-day cultured cotyledons. Selection with hygromycin and G-418 proved more efficient than kanamycin, with significantly lower percentages of shoots lacking GUS or VlmybA1-2 traits under G-418 and hygromycin selection. The “synchronized germination system” developed in this study has been applied to large-scale transformation using activation tagging vectors, and a large number of transformants was successfully obtained.

Zucchini is a unisexual plant that produces both male and female flowers, and the number of female flowers is higher in the upper node. Because the rate of female flower production increases over the long term, the number of fruits harvested and the yield can increase. Therefore, we investigated the relationship between the rate of female flowers, dry matter production, and fruit yield in long-term production over 168 days (from 7 Oct. 2020 to 24 Mar. 2021). The proportion of female flowers with nodes higher than the 40th was 86.2%, which was reduced to 67% or 50% by trimming the young female flowers. No significant difference in total dry matter production or the fraction of dry matter distributed to the fruit was observed between the untreated control and the 67% of female flower plants at the end of the experiment. The light extinction coefficient of the zucchini canopy was k = 1.05. The photosynthetically active radiation intercepted by the plants was estimated from the light extinction coefficient, leaf area index (LAI), and light use efficiency (LUE). The fresh fruit yield was the highest in the control plants and was 6.9 ± 0.2 kg·m⁻² at the end of the experiment. Although fresh fruit yield decreased in the 50% female-flower restricted plants, a difference in fresh fruit yield between the control and 50% female-flower restricted plants was not observed until 126 days after transplanting (DAT), i.e., 10 Feb. 2021. Therefore, the excess female flower rate in the upper node did not increase the fresh fruit yield under lower solar radiation. In this study, we estimated the values required to develop a model to predict fruit yield and a potential increase in yield during long-term zucchini production.

Predicting the harvest date and yield of vegetables substantially contributes to stable shipments; however, such practical applications regarding lettuce remain limited. This study aimed to improve the accuracy of lettuce growth sensing and harvest date prediction by using artificial intelligence to analyze aerial photographs captured by drones. In addition, the relationship between yield and area data from aerial images is discussed concerning the final goal of yield estimation. For the harvest date prediction, a convolutional neural network trained on images of lettuce with different leaf ages was used to construct a leaf age estimation system by applying it to a leaf age-increasing model for lettuce created from two years of data. Six production plots in two regions were targeted for practical predictions. Images were obtained by aerial drone photography from 14 to 21 days after planting and input into the system to estimate leaf age. A leaf age of 40 was predicted as the harvest day using the forecast and daily mean temperature values obtained from mesh agricultural weather data. The mean relative error between the predicted and actual harvest dates was 2.35 days within the target value of 3.5 days, indicating that harvest prediction was achieved with high accuracy. To estimate the yield, the relationship between yield and cultivated area was surveyed using drone aerial images of fertilizer-dependent growth plots. The results showed that vegetation coverage was more strongly correlated with yield than with the vertical projected area of plants. The correlation between vegetation coverage and yield was higher during the preheading period (leaf age 16.2) than during the early heading period (leaf age 25.1). Therefore, we suggest that the vegetation coverage in the before-heading period could be used as an explanatory variable for yield estimation. In conclusion, this study enabled the prediction of harvest dates during growth at a practical level and provided basic insights for yield estimation.

Although Basella alba and B. rubra have been used as annual leafy vegetables, ornamental plants, in dyes and in medicine for a long time in many countries, factors affecting seed germination in these species remain unclear. Therefore, in this study the effects of scarification treatment, temperature and light on seed germination were investigated in B. alba and B. rubra. In darkness, the germination percentage of scarified seeds was increased compared to non-scarified seeds in both species, suggesting that they show physical dormancy. Thermal optima for germination in B. alba and B. rubra were 25°C under dark conditions. In addition, light (white light) irradiation to seeds promoted germination, although they were able to germinate even if they were kept in darkness. It was also clarified in both species that the light quality of red (R) and far-red lights (FR) affected seed germination. Red light irradiation promoted seed germination, but far-red irradiation inhibited it. After far-red light irradiation for four days, the promotive effect of a red light on seed germination was reversed by a far-red light given immediately afterwards. Successive irradiation with R/FR/R promoted seed germination, but the subsequent FR irradiation cancelled the promotive effect of red light. Such reversible effects of red and fa-red light are typical in phytochrome-mediated seed germination in other species. Our results indicated that seeds of B. alba and B. rubra exhibit physical dormancy and light sensitive traits that are controlled by phytochrome(s), possibly phytochrome B.

Calcium (Ca) is an essential nutrient that regulates many physical events during plant growth, such as signaling and nutrition. Ca is known as an immobile element due to its binding properties with pectin. Ca deficiency during the vegetative process of plant growth causes physical disorders such as shoot apical meristem necrosis and leaf etiolation, which inhibit plant growth. Tomato plants lacking Ca also experience impaired fruit production due to blossom end rot (BER), although the symptoms of BER have reported to be alleviated by Ca resupply through foliar application. On the other hand, the mechanism remains for this unknown. Therefore, it is important to understand the effect of Ca reapplication on overall plant growth. To analyze the effect of Ca reapplication on plant growth, especially reproductive development, an experimental system was established in which the root Ca supply was interrupted for 30 days via hydroponic cultivation, followed by reapplication of Ca at a concentration of 0.6 mM, a level comparable to the control treatment. Regarding the difference in vegetative growth performance among treatments, based on the results of leaf SPAD measurements and biomass in the 80 days after Ca deficiency treatment, there was no significant difference between Ca reapplication and the control; however, Ca deficiency resulted in lower values. As for the difference in reproductive development, Ca reapplication treatment was found to produce 52% more fruit compared to the control and 78% more fruit than Ca-deficient plants. These results indicated that Ca reapplication to Ca-deficient individuals caused an increase in fruit production and restored vegetative growth performance.

Dahlia (Dahlia variabilis) flowers exhibit wide variety in terms of color, shape, and size; however, their short vase life limits their utility as ornamental plants. This study aimed to identify candidate genes related to flower senescence in dahlia using RNA-seq analysis. In total, 2,698 transcription factors were identified in dahlia flowers, with 114 genes belonging to the NAC family. Additionally, FPKM levels of five NAC transcription factors (DvNAC1, DvNAC2, DvNAC3, DvNAC4, and DvNAC5) increased from flowering to senescence (petal wilting) in the dahlia ‘Kamakura’. Therefore, the expression level of these NACs was investigated in three dahlia cultivars ‘Kamakura’, ‘Micchan’ and ‘Port Light Pair Beauty’ by real-time PCR. The expression level of all five NACs increased from flowering to flower senescence in the three cultivars. The increase in DvNAC1, DvNAC2, DvNAC3, and DvNAC5 expression was delayed in ‘Micchan’ compared to that in ‘Kamakura’ and ‘Port Light Pair Beauty’. This delay in DvNAC1, DvNAC2, DvNAC3, and DvNAC5 expression corresponded with ‘Micchan’ having a longer vase life than the other two cultivars. Furthermore, ethylene treatment accelerated flower senescence and increased NACs expression, except for DvNAC4, while 1-methylcyclopropene delayed both flower senescence and the increase in NAC expression in the three cultivars. These results indicate that NAC transcription factors, especially DvNAC1, DvNAC2, DvNAC3, and DvNAC5, are likely to be genes associated with flower senescence in dahlia.

6′-Deoxychalcone (isoliquiritigenin and butein) is a yellow flavonoid pigment that is promising target for molecular breeding of yellow flowers. In our previous study, it was suggested that co-overexpression of CaMYBA, a positive anthocyanin MYB transcription factor in pepper (Capsicum annuum) with a dahlia (Dahlia variabilis) aldo-keto reductase (AKR) DvAKR1 and snapdragon (Antirrhinum majus) chalcone 4′-O-glucosyltransferase (4′CGT) Am4′CGT was sufficient to accumulate isoliquiritigenin. However, CaMYBA expression induced not only accumulation of 6′-deoxychalcone, but also that of delphinidin-based anthocyanin. Since this anthocyanin accumulation is unnecessary for molecular breeding of yellow flowers, it is necessary to identify genes important for the accumulation of only 6′-deoxychalcone. In this study, we conducted comparative RNA-seq analysis between co-overexpressing CaMYBA, DvAKR1, and Am4′CGT (referred as the CaMYBA combination) and co-overexpressing NtAN2, DvAKR1, and Am4′CGT (referred as the NtAN2 combination) Nicotiana benthamiana leaves. The CaMYBA combination successfully induced isoliquiritigenin, while the NtAN2 combination failed to do so. Because the NbCHS2 gene was detected as a differentially expressed gene, CHS genes from N. benthamiana, pepper, and dahlia were co-overexpressed with DvAKR1 and Am4′CGT. Our results reconfirm that CHS plays an important role in the accumulation of isoliquiritigenin, but the detected peak of isoliquiritigenin was small, also indicating that other genes are required for the abundant accumulation of isoliquiritigenin. We also analyzed NbPAL4, which was more highly expressed in the CaMYBA combination than in the NtAN2 combination, but our results indicated that NbPAL4 is not essential for isoliquiritigenin accumulation. Finally, we investigated why the NtAN2 combination did not work for isoliquiritigenin and anthocyanin accumulation. RNA-seq analysis indicated one bHLH transcription factor was down-regulated in the NtAN2 combination, so we co-overexpressed a dahlia bHLH transcription factor DvIVS with the NtAN2 combination. Isoliquiritigenin accumulation was successfully detected suggesting that the failure of isoliquiritigenin accumulation in the NtAN2 combination is due to the weak ability of NtAN2 to activate bHLH transcription factors.

Early-bolting in summer is a major problem when growing delphinium seedlings in summer to produce cut flowers that will be shipped in autumn and winter. In this study, an intermittent low-temperature storage (ILTS) treatment that induces flower bud differentiation in strawberry and prevents rosette formation in Eustoma significantly increased the Delphinium elatum cut flower length. Moreover, ILTS was as effective as growing seedlings under cool conditions at preventing early-bolting. We analyzed the effects of six ILTS treatments that differed regarding the treatment temperature (5 and 10°C) and treatment cycle (3 days/3 days, 6 days/6 days, and 12 days/12 days; ambient conditions/cool and dark). Cut flowers were significantly longer with the 6 days/6 days treatment at 10°C than for the control treatment. Furthermore, repeating the ILTS treatment cycle (6 days ambient conditions/6 days at 10°C) a total of four times produced high-quality cut flowers regardless of the cultivar. Therefore, this ILTS treatment may be ideal for preventing early-bolting in D. elatum.

This study investigated the time and duration effects of night cooling period on plant growth and flowering to optimize cooling techniques for potted marguerite lines, focusing on the widely grown cultivars ‘Sunday Ripple’ and ‘Furenka’, which are known for their early-flowering traits and commercial significance. Three cooling treatments—overnight, end-of-day (EOD, 4 h post-sunset), and end-of-night (EON, 4 h pre-sunrise) cooling—were compared with a non-cooled control. The EON-cooling treatment accelerated flowering and reduced the leaf number in ‘Sunday Ripple’, while the EOD-cooling treatment produced similar effects in ‘Furenka’. Subsequent experiments evaluated the effects of 4-h nightly exposure to 21°C at different time periods on growth, flowering, and flower bud differentiation and development. Both EOD-21°C and EON-21°C treatments promoted flower bud differentiation in ‘Sunday Ripple’, with the EOD-21°C treatment proving most effective for ‘Furenka’. The final experiment investigated the optimal period of time and duration of the nighttime cooling. In ‘Sunday Ripple’, days to bud formation and flowering remained unaffected during both the first (FC, starting 5 weeks post-pinching) and the second (SC, starting 6 weeks post-pinching and lasting for 5 weeks) cooling periods, compared with those of the non-cooled control. However, in ‘Furenka’, EOD-cooling during the first cooling period (EOD-FC) accelerated flower budding and flowering similar to those in the continuous EOD-cooling (EOD-C) treatment and resulted in earlier flowering than that in the control. The EON-cooling and EOD-FC treatments are expected to substantially reduce cooling degree hours (CDH) compared with those needed with overnight cooling. These results show that EON-cooling for ‘Sunday Ripple’ and EOD-FC for ‘Furenka’ effectively promoted flowering. Additionally, these cooling techniques significantly reduced production costs, highlighting their potential as efficient cultivation methods for high-temperature conditions. Our study offers practical solutions for mitigating delayed flowering, a prevalent production challenge in high-temperature conditions.