Dwarfing rootstocks are widely used in apple cultivation. We focused on adventitious rooting, crucial for vegetative propagation, and the phloem-to-xylem ratio, an indicator of dwarfing. Malus prunifolia and M. domestica ‘M.9’ were used as vigorous rootstocks with adventitious rooting ability and dwarf rootstocks without it, respectively. QTL analysis showed that QTLs for adventitious rooting (Cp) and the phloem-to-xylem ratio (Rb4) were located in the same genomic region, suggesting a potential relationship between the traits. The exon-intron structure, cDNA, and predicted amino acid sequences of the genes in the regions narrowed down by fine mapping for Cp were analyzed along with their expressions during cutting. Long transposable element-like insertions were found in MD17G1113200 and MD17G1113300 on the M. prunifolia genome unlike M. domestica. The gene product of MD17G1113300 in M. prunifolia was predicted to be 384 amino acids shorter than that of M. domestica in the C-terminal region, with different expression levels between the species during cutting. In MD17G1113900, functional amino acid substitutions and different expression levels during cutting were found between the species. When comparing other candidate genes for Cp between the species, different expression levels during cutting were found in MD17G1113400, MD17G1113500, and MD17G1113600. The physiological roles of these candidate genes and their relationships with adventitious rooting ability are discussed. Stereomicroscopic observation of the bases of cuttings revealed distinct morphological characteristics of M. prunifolia compared with M. domestica in terms of callus formation and rooting from lenticels and calli. Fully understanding the mechanisms determining adventitious root formation and developing highly accurate DNA markers are anticipated in the near future, and this paper will serve as a foundation for these achievements.

Chili pepper (Capsicum spp.) is an economically important crop used as a spice and vegetable. The striking feature of chili pepper fruits is their pungency, which is attributed to capsaicin and its analogs (collectively called capsaicinoids). Capsaicinoids are unique compounds synthesized only in Capsicum fruits, and their biosynthesis exhibits temporal- and spatial-specific patterns in the placental septum tissue. Capsaicinoids are biosynthesized through the condensation of vanillylamine (produced in the phenylpropanoid pathway) and a fatty acid moiety (produced from branched amino acids). Capsaicinoids have beneficial bioactivities, such as thermogenetic and anti-obesity properties, and thus they are regarded as health-promoting compounds. Furthermore, low-pungent capsaicinoid analogs (capsinoids and capsiconinoids) have been discovered in chili pepper fruits. They exhibit similar physiological activities to pungent capsaicinoids and are promising compounds with high economic value because of their low-pungency. Huge variation in capsaicinoid and analog contents among Capsicum accessions has been observed. Research using various Capsicum accessions has identified important genetic factors in the biosynthesis of capsaicinoids and low-pungent analogs. This review provides an overview regarding the biosynthesis of capsaicin and its analogs. Furthermore, future options to enrich the quality of chili pepper fruits are discussed.

Soilborne pest and disease management is one of the most important challenges in the cultivation of sweet bell pepper, sweet pepper, and chili pepper (Capsicum annuum L.). In Japan, the nematode Meloidogyne incognita is a soilborne pest responsible for considerable economic losses. Unfortunately, although F₁ rootstock cultivars resistant to M. incognita infestation have been developed, resistance-breaking populations of M. incognita have emerged that can attack these cultivars. To address this issue through crossbreeding, breeding materials that are resistant to the new populations of resistance-breaking nematodes are needed. Here, we obtained 288 Capsicum germplasms from the NARO Genebank (Japan) and screened them for resistance to infestation by normal nematodes (strain Mi-Nishigoshi), resistance-breaking nematodes (‘LS 2341’-derived strain), and nematodes collected from 14 sweet pepper fields in Miyazaki Prefecture, Japan. Two of the germplasms, ‘NuMex Bailey Piquin’ and ‘PM 217-1-3’, showed strong resistance to all of the M. incognita tested and were used for progeny testing. ‘NuMex Bailey Piquin’ was selected as the parental line for a new F₁ rootstock with resistance to a wide range of nematodes, including resistance-breaking nematodes. Since segregation of resistance was observed in ‘NuMex Bailey Piquin’, we selected one line named ‘J159’ among the selfing population of ‘NuMex Bailey Piquin’ to fix the resistance to the resistance-breaking nematode. We then evaluated the nematode resistance of ‘J159’ F₁s crossed with the doubled haploid line ‘KLDH89’, which is resistant to bacterial blight, normal nematodes, and pepper mild mottle virus (pathotype P_1,2), but not to resistance-breaking nematodes. The ‘KLDH89 × J159’ cross not only showed high resistance to resistance-breaking nematodes, but also high yield when used as a rootstock. It is registered in Japan under the rootstock cultivar name ‘Dai-Hinata’.

Short-term, low-truss (STLT) crop management is used in commercial greenhouses in Japan, usually for greenhouse tomatoes for year-round harvest and sale. When STLT crop management was first developed, it was used to produce high-Brix tomatoes by managing stress control through water and nutrient supply. It has recently been used by regular tomato growers. In STLS crop management, light use efficiency was significantly and positively correlated with CO₂. Based on this relationship, dry matter (DM) production was predicted and the predicted DM was not significantly different from the observed DM when the average daytime CO₂ concentration ranged mainly between about 400 and 650 μmol·mol⁻¹. In STLT crop management, there was no significant difference in DM production between high Brix and regular tomatoes. Thus, in high Brix tomatoes, only a significant increase in fruit DM content induced a significant reduction in fruit fresh weight and increase in fruit Brix. In plants grown with salinity treatment, fruit Brix was significantly and highly correlated with the cumulative electrical conductivity (EC) of the drainage (cEC_d). Fruit Brix could be predicted and controlled based on cEC_d. Originating in Japan, high-Brix tomato production has reached Europe and other Asian countries, where demand is expected to increase. STLT crop management will support this increase. Models for yield and Brix could help growers.

Paprika (Capsicum annuum L.) is known for its abundant functional components such as carotenoids and phenolics. Growth responses to nutrient conditions including nitrogen (N) have been studied. However, there has been only limited analysis on the variations in components in response to N. This study investigated the effects of different N levels on the functional components of paprika. Paprika was grown under different N conditions and ripe fruits were harvested. Subsequently, mineral, carotenoid, phenolics, and sugar contents were measured. Higher N supply increased fruit weight and carotenoids, but reduced phenolics and glucose. The negative correlation between carotenoids and phenolics suggests complementary antioxidant functions in fruits, while the significant association between these metabolites and boron and potassium implies that these elements may have indirectly influenced metabolic pathways. Moreover, specific components like phenolics indicate a trade-off with yield. Capsanthin alone was significantly affected by N supply, suggesting downstream effects on the carotenoid biosynthetic pathway. This study will contribute to the optimization of N fertilizer application for balanced paprika production with high quality and economic yield.

Kiwifruit flowers have approximately 40 stigmas. Artificial pollination is essential for dioecious kiwifruit production. We investigated the effect of the pollination site on seed distribution, fruit size and quality. We found that seeds should be evenly distributed in the fruit to improve fruit shape and that seed number and total soluble solids (TSS) were not positively correlated. We also noted that seeds were distributed in a spreading manner away from pollinated stigma. This indicated that the stigma and carpel had a similar one-to-one like connection. However, the connection was not exact, and seeds were distributed not only in a particular carpel, but also slightly the outside the carpel. Seeds were distributed uniformly in the fruit even when pollination was limited to the two most distant stigmas, and the number of seeds increased when the number of pollinated stigmas increased. These results indicated that it was not necessary to pollinate all stigmas, but only several stigmas, in order to achieve larger fruit size.

Ca²⁺ indicators, such as GCaMP6, have been primarily developed for animal research, and with limited applications in plants, they mainly target the vegetative organs of Arabidopsis and tobacco. Therefore, we focused on utilizing GCaMP6 in tomato fruit. Our observations revealed changes in fluorescence intensity upon cutting, as well as exposure to glutamate and EGTA, indicating that is possible to effectively measure the cellular Ca²⁺ concentration of GCaMP6-transformed tomato plants. The enhanced fluorescence intensity patterns under cold and salt stress imply that Ca²⁺ signals trigger responses to abiotic stress in fruit, with the salt stress response being organ-specific. Investigating the relationship between Ca²⁺ signaling and sugars, we found that glucose and fructose induce Ca²⁺ signaling in tomato fruit, with a response pattern dependent on sugar concentration. Moreover, a comparison of Ca²⁺ levels using corrected fluorescence intensity values during early fruit development, which is a critical stage for fruit physiology and the occurrence of disorders, revealed lower levels in the blossom end compared to the stem end 15 days after flowering. Using Ca²⁺ indicators in fruit has the potential elucidate the connection between Ca²⁺ and horticulturally important traits in fruits.

Fruit sensory characteristics are crucial in terms of decision-making for fruit production and breeding. However, due to the relatively short consumption history of blueberries in the Japanese market, their sensory characteristics have yet to be characterized by Japanese consumers. Over three years, Japanese consumer panels evaluated preferences and sensory attributes of 34 blueberry cultivars such as rabbiteye blueberry (Vaccinium virgatum Aiton) and highbush blueberry (V. corymbosum L.), including both northern highbush blueberry and southern highbush blueberry. The preferences and sensory attributes were rated using the general labeled magnitude scale (gLMS) method. The consumer panels recognized variations in sensory attributes and expressed their preferences for taste and texture. Overall liking was strongly correlated with texture liking (r = 0.66), sweetness (r = 0.58), and flavor intensity (r = 0.42), but weakly with firmness (r = 0.22) and not correlated with sourness or a rough feeling. Additionally, significant interaction effects between perceived and ideal taste intensities on overall liking were found, with sourness perception having a more pronounced effect. The results also suggested potential differences in blueberry preference between Japanese and U.S. consumer panelists. Furthermore, sensory attributes were well correlated with corresponding instrumentally measured taste and texture traits, supporting the usefulness of biochemical and mechanical measurements for evaluating blueberry quality characteristics, particularly texture. This study revealed that blueberry fruit preference was largely determined by sweetness intensity and texture preference, with sourness preference also having a significant influence. There is potential to satisfy Japanese preferences, especially regarding texture. The findings provide valuable insights into Japanese consumer preferences for blueberries and offer a roadmap for consumer-oriented cultivar selection and breeding.

Fruit consumption is highly recommended due to its health benefits. Passiflora species are a good source of vitamins and antioxidant compounds such as carotenoids that are associated with a reduction in cellular oxidative processes, as well as against cardiovascular diseases and cancer development. As a result, purple passion fruit (P. edulis) and yellow passion fruit (P. edulis f. flavicarpa) are economically important crops that are cultivated based on the demand for their flavor and nutraceutical properties. The objective of this study was to determine the components of carotenoids and sugars in the pulp juice of passion fruit. Two Ecuadorian yellow passion fruit strains (‘INIAP 2009’ and ‘POR1’), one Ecuadorian purple passion fruit variety (‘Gulupa’) and two Asian hybrid cultivars (P. edulis × P. edulis f. flavicarpa; ‘Summer Queen’ and ‘Ruby Star’) were used for this research. The results showed that ‘POR1’ had high acidity and contained all carotenoids, but had the lowest amount of vitamin C, whereas ‘INIAP 2009’ had high contents of organic acids, vitamin C and β-cryptoxanthin. ‘Gulupa’ had the lowest acidity, α-carotene and citric acid content, but the highest amount of glucose, fructose, malic acid and vitamin C; this variety also showed high values of β-carotene and β-cryptoxanthin. On the other hand, ‘Summer Queen’ had high sucrose, malic acid, α and β-carotene and good amount of vitamin C, while ‘Ruby Star’ had high amounts of α-carotene, β-cryptoxanthin and citric acid, but low vitamin C content. These results can be used for further breeding programs focused on improving passion fruit quality.

The cultivation of ‘Muscat Bailey A’ for fresh consumption is popular in western Japan, but growers are facing issues with poor coloration of grape berries partly due to insufficient cooling of nighttime temperatures. To ameliorate the coloration defects in ‘Muscat Bailey A’ grapes grown with gibberellin treatment for seedlessness under high nighttime temperatures, and to improve the color characteristics of red wine made from these grapes, the effectiveness of agricultural materials aimed at correcting poor coloration was tested on grape berries intentionally subjected to conditions that induce poor coloration in 2017 and 2018. Inactivated yeast derivatives, shochu lees filtrate, and proteolytic enzymes were sprayed on leaves, and fertilizer containing optically active abscisic acid (S-ABA) was sprayed on clusters during veraison as agricultural materials that could potentially improve fruit characteristics such as grape skin color and the hue of wine. After veraison, the grapes were grown under conditions in which the nighttime temperature was kept above 25°C. The L*, a*, and b* values of these grape skins were determined using colorimetry. Low L* values, indicating darker berry coloration, and notable decreases in hue angle, suggesting a shift towards red and purple hues, were observed after treatment with S-ABA-containing fertilizer. The absorbance of wine made from the grapes described above was measured spectrophotometrically. A significant difference in the color characteristics of the wine was observed for various absorbance indices (A₄₂₀ representing yellow, A₅₂₀ representing red-purple, and A₅₂₀, at pH 1.0 as an indicator of total anthocyanins). The tannin content in the wine from S-ABA-treated grapes was significantly higher compared to the control. However, no differences were observed in taste among these wines. Comprehensive analysis by LC-MS confirmed that mainly levels of malvidin, petunidin (both purple-colored anthocyanins), and peonidin (a red-colored anthocyanin) compounds had increased. These results suggest that S-ABA-containing fertilizer works effectively in alleviating the poor coloration of ‘Muscat Bailey A’ clusters grown under high nighttime temperature conditions and in improving coloration of the wine made from these grapes.

Spinach for processing use should be systematically harvested according to the fresh weight and height standards required by the processing plant; thus, monitoring spinach growth in fields is crucial. However, ground measurements require substantial labor. In recent years, unmanned aerial vehicles (UAVs) have been established as effective labor-saving tools for monitoring crop growth. This study aimed to clarify: 1) which model and image type are appropriate for mono-regression in the estimation of fresh weight and height of processing spinach, 2) whether a combination of images from RGB and multispectral cameras and the application of machine learning can improve the estimation accuracy in multivariate regression, and 3) which model shows the highest estimation accuracy over extrapolation data. In the mono-regression, the highest fresh weight estimation accuracy was achieved with the soil adjusted vegetation index (SAVI) using a multispectral camera at 50 m altitude (test root mean squared error (RMSE) = 0.795). The highest height estimation accuracy was achieved with the modified green red vegetation index (MGRVI) using an RGB camera at 50 m altitude (test RMSE = 5.01). Estimation accuracy was highly dependent on image type, suggesting that the effectiveness of appropriate selection for accurate estimation. In multivariate regression, machine learning models showed higher accuracy for fresh weight estimation compared to multiple linear regression. Although most support vector regression models exhibited higher accuracy than that of the multiple linear regression model, random forest regression models exhibited lower accuracy for height estimation. These findings suggest that the selection of an appropriate model type is critical. Although combining images from RGB and multispectral cameras improved accuracy in machine learning models, the effects were inconsistent because of other factors including target traits, model types, and UAV altitude. After comparing all models with the highest accuracy in each category, the fresh weight estimation model developed using support vector regression with images from an RGB camera at 30 m altitude, and the height estimation model based on support vector regression with images from both cameras at 30 m altitude showed the highest accuracies (test RMSE = 0.720 and 4.19, respectively). These machine learning-based models can thus facilitate precise monitoring of the fresh weight and height of spinach for processing use.

Broccoli produces green florets under normal growth conditions, but produces darkish-colored florets after low-temperature exposure due to the accumulation of anthocyanin, which often reduces its commercial value. Selecting anthocyanin-free genotypes requires exposing the florets to low temperatures, which is laborious and time-consuming. We identified a genomic region on chromosome C09, which was associated with anthocyanin pigments in florets at low temperatures, through quantitative trait locus sequencing (QTL-seq) analysis using the phenotype data obtained from field evaluation of anthocyanin pigments of F₂ plants over two years. Among nine differentially expressed genes in the QTL region, one gene encoding flavonoid 3′-hydroxylase (F3′H) was selected as a candidate. Sequence analysis of Brassica oleracea F3′H (BoF3′H) of parental lines revealed the presence of three alleles, with one derived from the anthocyanin-free parents, Bof3′h-2, exhibiting a 43-bp deletion in the second exon, causing a frame-shift mutation. Designing DNA markers capable of distinguishing this mutation, we demonstrated that, among 35 F₁ cultivars released in Japan, eight homozygous for the Bof3′h-2 allele showed no anthocyanin pigments and lower anthocyanin contents in florets in the autumn- to over-winter harvesting. The expression level the BoF3′H gene was not necessarily related to the difference in anthocyanin contents. Furthermore, seedlings of the Arabidopsis f3′h mutants exhibited no pigments and a significantly reduced anthocyanin content under low-temperature treatment compared to that in the wild type. These results suggested that the 43-bp deletion in BoF3′H is responsible for the anthocyanin-free trait in broccoli genetic resources, and the developed marker was deemed useful for marker-assisted breeding.

The Freestone-Melting flesh (F-M) locus in peach controls two strongly linked traits that have significant effects on fruit quality: pit adhesion (freestone/clingstone) and flesh type (melting/non-melting). Recently DNA markers have been developed to identify major haplotypes of M0, M1, M2, M2b, and M3 at this locus. Japanese peach cultivars were historically developed using cultivars introduced from overseas; however, how the haplotypes have changed at the F-M locus during major cultivar improvement remains unknown. In this study, we aimed to clarify the transition of haplotypes at the F-M locus in major varieties of peach cultivars from the past to the present. First, we modified the F-M locus haplotype genotyping method by multiplexing the PCR to genotype many cultivars efficiently. Then, we genotyped the F-M locus of 63 cultivars, including major cultivars in 1934, 1980, and 2020 using this method. The results show that the number of cultivars harboring the M1 haplotype, which is a dominant freestone haplotype, decreased significantly, and cultivars homozygous for the M0 haplotype dominated. Haplotypes other than M0 and M1 were infrequent among major cultivars. Cultivars harboring M1 have not always been evaluated as freestone in the literature, while we found a strong relationship between the presence of the M1 haplotype and the freestone trait. All the genetically non-melting cultivars were evaluated as non-melting. There has been only one case in which a genetically melting cultivar was previously evaluated as semi-melting, although all other genetically melting cultivars were evaluated correctly. This result suggests that DNA markers could be effective for freestone breeding and there were no major problems in flesh texture prediction using this marker system. The haplotype transition at the F-M locus during Japanese peach breeding elucidated in this study could lead to new research on freestone/clingstone and flesh texture traits and their application in breeding.

Persimmon fruit synthesizes and accumulates proanthocyanidins (PAs), resulting in its astringent taste. The pollination-constant and non-astringent (PCNA) trait is conferred by recessive alleles at the ASTRINGENCY (AST) locus, which has been exploited to control PA accumulation of persimmon fruit. However, some individuals with recessive homozygosity at the AST marker locus in breeding populations produce mature fruit with astringency, thereby reducing the marker-selection efficiency for the PCNA trait. In this study, we genetically and physiologically characterized the predicted ast-homozygous individuals exhibiting strong astringency in a cross population of ‘Taigetsu’ (non-PCNA) and ‘Kanshu’ (PCNA). The fruit PA content of these astringent individuals was higher than that of the other PCNA fruit, but lower than that of the non-PCNA fruit. These astringent individuals were similar to the other PCNA plants in terms of tannin cell size. Gene expression analysis revealed that PA synthesis-related genes (e.g., DkMYB4, DkMYC1, and DkANR) were expressed at a higher level in the astringent individuals than in the other PCNA fruit during the early fruit development stage. Furthermore, in the presumed ast-homozygous individuals with various PA contents, the expression of cellular function-related genes was highly correlated with PA accumulation. These genes may be important for tannin cell development and PA synthesis, potentially offering a novel approach to further modulate astringency in persimmons.

Pear scab, a fungal disease caused by Venturia nashicola, is the most serious disease in Asian pear production, leading to decreases in yield and fruit quality. Five major scab resistance genes (Rvn1–Rvn4 and Vnlf) and two QTLs (Rvn5 and Rvn6) identified from different cultivars have been used in pear breeding programs to produce resistant cultivars. Here, we validated the effectiveness of three simple sequence repeat (SSR) markers (LFA02a04, LFA02a09, and LFA02b20) linked to Vnlf (possibly allelic to Rvn2) by using 29 cultivars and four breeding populations. Since there was little discrepancy between the phenotype and genotype in any of the breeding populations, with the frequency of correct classification ranging from 89% to 100%, these markers will be useful for breeding programs. In a population segregating for Rvn1 and Vnlf, the ratio of resistant to susceptible individuals fitted a 3:1 model, confirming that both genes are dominant. Although symptoms with sporulation were observed on leaves of some individuals with only Rvn1 and on those with no resistance gene, no sporulation was observed on leaves of gene-pyramided individuals (Vnlf + Rvn1) or on those carrying only Vnlf. Moreover, we revealed that resistant Chinese pear (Pyrus bretschneideri Rehder) ‘Changxili’ is heterozygous for a previously unidentified host-resistance gene that behaves as a single dominant gene with the observed segregation ratios in four progeny populations. These segregation results in combination with marker data suggest that this newly discovered gene, designated Rvn7, is at a locus distinct from both Rvn1 (derived from ‘Kinchaku’) and Rvn4 (derived from ‘Hongli’). We expect these findings to contribute to pear breeding programs working to develop resistant cultivars with single and multiple resistance genes.

In recent years, due to an aging workforce and labor shortages in the agricultural sector, coupled with difficulties in finding work in the welfare sector, agriculture-welfare collaboration has been promoted in Japan. However, owing to a lack of understanding in the agricultural sector about the abilities of individuals with disorders and how to deal with them, it has been assumed that individuals with disorders are unable to perform agricultural work. To address this lack of knowledge, in this study, 45 participants with intellectual disorders (Medical Rehabilitation Handbook A: 6 and B: 39) and 12 with mental disorders (Mental Disability Certificate Level 1: 1, Level 2: 8, and Level 3: 3) were asked to perform three tasks of varying difficulty levels in citrus orchards (bagging, harvesting, and fruit thinning). Their work abilities were evaluated based on measurements of work efficiency and observations of their work. The results showed that 96%, 50%, and 40% of the participants with disorders were able to comprehend the bagging (low difficulty), harvesting (medium difficulty), and fruit thinning (high difficulty) tasks, respectively. The average efficiencies of participants with disorders who comprehended the tasks were 55%, 71%, and 111% of those without disorders for bagging, harvesting, and fruit thinning, respectively. For fruit-thinning, six participants were more efficient than all participants without disorders. As described above, some aspects of the work efficiency of individuals with disorders at the start of the initiative were clarified. In the future, it will be necessary to clarify the negative effects of long work hours on physical strength and concentration, as well as on efficiency gains, through further experience and work process innovations.