The pineapple (Ananas comosus (L.) Merr.) is an economically important tropical fruit crop. In this study, we performed quantitative trait locus (QTL) analysis using 168 individuals of the F₁ population of ‘Yugafu’ × ‘Yonekura’ for 15 traits: leaf color (L*, a*, b*), harvest day, crown number, slip number, stem shoot number, sucker number, fruit weight, fruit height, fruit diameter, fruit shell color, soluble solid content, acidity, and ascorbic acid content. The constructed single-nucleotide polymorphism (SNP)-based genetic linkage map consisted of a total genetic distance of 2,595 cM with 3,123 loci, including 22,330 SNPs across 25 chromosomes. QTL analysis detected 13 QTLs for 9 traits: leaf color a*, harvest day, fruit weight, fruit height, fruit diameter, fruit shell color, soluble solid content, acidity, and ascorbic acid content. The causative gene for each QTL was predicted with two genes identified as candidate genes. The AcCCD4 gene on Aco3.3C08 was the predicted causative gene for the shell color QTL, which negatively controls shell color by carotenoid degradation. The Myb domain protein-encoding gene on Aco3.3C02 was the predicted causative gene for shell color and leaf color a* QTL, which positively regulates anthocyanin accumulation. The QTL and gene information provided here contributes to future marker-assisted selection for fruit quality.

The salak fruit (snake fruit) contains one to three seeds covered with an aril. The size of the fruit primarily depends on the number of seeds. Fruits with more seeds grow larger and attain higher commercial value in fresh markets owing to their superior appearance. In eastern Thailand, during the hot period in the early rainy season, the fruit set of salak decreases, which is empirically believed to be caused by high night temperatures. In this study, we pollinated and incubated salak spadices at various temperatures (18–36°C) to determine the optimal post-pollination temperature range needed to produce valuable fruits. Chronological pollen-tube elongation in the pistil and development of the early embryo and endosperm were then observed anatomically, followed by fruit-set estimation. At ≤ 21°C, pollen-tube elongation was limited. At 24–27°C, although elongation was slow, pollen tubes attained embryo sacs in > 60% of florets within 36 h after pollination. Pollen tubes elongated fastest at 30–33°C and attained embryo sacs within 12 h after pollination. At 36°C, the difference in the elongation speed tended to be higher among the pistils. The percentages of ovules with developing embryos were the highest at 27°C at 48 h after pollination; zygote and early embryos were observed in 10.8% and 55.9% of the ovules, respectively, and the primary endosperm nucleus, dispersing endosperm nucleoplasm, and free endosperm nuclei were observed in 8.6%, 38.7%, and 19.4%, respectively. The second highest percentage was observed at 24°C. The percentages tended to decrease at 30°C and decreased significantly at ≥ 33°C. At ≥ 30°C, shriveled embryo sacs were observed. The estimated fruit-set percentage based on embryo development as the consequent fruit set was the highest (≈80%) at 27°C, while the second highest percentage (≈75%) was at 24°C. At ≥ 30°C, the estimated percentage decreased to less than half that at 27°C. Fruits containing three seeds were expected to grow in the range of 17.6–28.0% at ≤ 27°C. One- or two-seeded fruits were expected to grow at ≥ 30°C. Limited fruit set was expected at 36°C. Our results indicate that salak prefers relatively cool temperatures of approximately 25°C for the fertilization and set of valuable fruits.

‘Miyagawa-wase’ (Citrus unshiu Marcow.), an early-season citrus variety, is rich in multiple nutrients and widely consumed in Japan. In ‘Miyagawa-wase’, when the pulp reaches maturity and is ready to eat, the peel is still a greenish color because of the relatively high temperature in the harvest season. In this study, to improve the coloration of ‘Miyagawa-wase’ peel, we treated the fruit with 1-naphthaleneacetic acid (NAA) after harvest. The results showed that postharvest treatment with NAA was effective to induce chlorophyll degradation and carotenoid accumulation in ‘Miyagawa-wase’ peel during storage. In the NAA treatment, the reduction in the chlorophyll contents after harvest was in parallel with decreases in the expression of chlorophyll biosynthetic genes (CitGGDR, CitCHLH, CitCHL27, CitPORA, and CitCAO) and an increase in chlorophyll degradation gene CitPPH. The contents of the major carotenoids, β-cryptoxanthin and 9-cis-violaxanthin, were increased by the NAA treatment through upregulation of the expression of carotenoid biosynthetic genes (CitPSY, CitPDS, CitZDS, CitLCYb2, and CitHYb) after harvest. In addition, it was found that the positive effect on degreening in the NAA treatment was inhibited by the ethylene antagonist 1-MCP. In the combination treatment using NAA and 1-MCP, the total chlorophyll content was much higher, while the contents of β-cryptoxanthin and 9-cis-violaxanthin were lower compared with NAA treatment alone, indicating that the acceleration of degreening by NAA may be caused by ethylene. The results presented in this study suggest that postharvest NAA treatment is an effective method for improving the peel coloration in early-season citrus varieties.

Passion fruit (Passiflora edulis) is a tropical fruit that can be consumed fresh or processed. It is a typical respiratory climacteric fruit which is highly perishable because of the loss of water that causes dehydration and thus shrinkage, affecting the fruit appearance; in addition, some quality traits such as fruit weight, firmness and vitamin C content can also be influenced. Therefore, this fruit has a short shelf life. Storage in low temperatures has been assessed to extent the passion fruit shelf life remaining its fruit quality traits; however, information about the application of the hypobaric method in this fruit is null. The objective of this research was to evaluate the physical and chemical characteristics of the yellow and purple passion fruit under hypobaric storage conditions in low temperature. Results showed the hypobaric method had a positive effect in decreasing fruit weight loss, declining the loss of firmness, and reducing the degradation of vitamin C during the storage period. It decreased the evolution of ethylene which is positive to delay fruit senescence, and the production of CO₂. Finally, it was the only method which avoids the shrinkage completely in the purple passion fruits (‘Gulupa’, ‘Summer Queen’, and ‘Ruby Star’) and showed minor shrinkage in ‘POR1’ (yellow passion fruit). This method is considered as a promising technique to improve fruit storage.

Passion fruit (Passiflora spp.) vines, mostly indigenous to tropical highlands, although some species can be cultivated in tropical lowlands, are susceptible to high temperatures. To increase the resilience of passion fruit to the warming climate, there is an urgent need to evaluate existing genetic resources for traits suited to high temperatures and to efficiently select the superior genotypes. We investigated the genotypic variation in leaf photosynthetic reduction at high temperatures (> 30°C) as a base target trait for warming climates. Leaf photosynthesis and dark respiration were measured at 30–45°C leaf temperatures for 13 genotypes from various Passiflora spp. using a portable gas exchange system. Temperature-net and -gross photosynthetic rate curves were plotted, and the relationships between the photosynthetic rate and the transpiration rate and stomatal conductance were analyzed. The net photosynthetic rate decreased with reduced stomatal conductance and transpiration rate as the leaf temperature increased from 30°C to 40°C. Up to 45°C, the net photosynthetic rate continued decreasing with increasing dark respiration rate, whereas the gross photosynthetic rate tended to stop decreasing as the stomatal conductance and transpiration rate stopped decreasing. The respiration load of photosynthesis varied among genotypes: Alata seedling #1 (P. alata) and ‘MaQuatro’ (P. edulis f. flavicarpa) showed the lowest load, together with the smallest reduction in photosynthetic rate at high temperatures, while the Iriomote strain (P. laurifolia) showed the largest load despite the smallest reduction in photosynthetic rate. Although the trend in the physiological response to high temperatures was similar among genotypes, the rate of leaf photosynthetic reduction at high temperatures varied among passion fruit genotypes both inter- and intra-specifically. Reduction of the photosynthetic rate at high temperatures was significantly correlated with stomatal activity under non-stress conditions at 30°C leaf temperature. Stomatal length was closely correlated with photosynthetic and transpiration rates at higher leaf temperatures in the P. edulis group, whereas no correlation was detected when including the lowland relatives. We concluded that genotypes showing higher stomatal conductance and transpiration rates at 30°C leaf temperature maintained a higher leaf photosynthetic rate at temperatures > 40°C, providing potential indicators for screening.

The future impacts of climate change on the yields of staple crops have been widely investigated. However, owing to insufficient data compared to that available for staple crops and the complexity of the quality determination process, the relationship between quality changes in horticultural crops and climate change has not been quantified, and potential future changes in fruit quality are not well understood. We conducted temperature treatment experiments to quantify the sensitivity of apple quality to air temperature and collected quality indices records through field observations to propose a model for estimating apple quality indices from the air temperature. In the temperature treatment experiment, ‘Fuji’ apple trees were placed in glass chambers set at a constant temperature of 17.3–25.6°C from 110 days after full bloom (DAFB). The fruits were harvested at 170 DAFB to measure the quality indices. The results indicated that the acidity and ratings for blush, peel ground color, starch disappearance, and watercore were all significantly lower at higher air temperatures. The relationship between these quality indices and air temperature could be linearly approximated. Sugar content and fruit firmness were not clearly affected by the air temperature. In addition, data from field observations conducted at experimental orchards in Aomori and Nagano Prefecture over 50 years (1970–2019) were analyzed. The relationship between fruit quality indices at 170 DAFB and the mean temperature in the 60 days from 110 DAFB in Aomori and Nagano was similar to that observed for the chamber experiment results, and no significant difference was observed in the slope of the linear regression equation between the chambers and orchards. A model was developed to estimate the fruit quality indices based on air temperature by accumulating daily amounts of change in quality indices calculated from daily mean temperatures using the results of experimental and field observations. The model could be used to assess the impact of future long-term temperature increases on apple quality indices.

Prunus fruit trees of the Rosaceae family exhibit S-RNase-based gametophytic self-incompatibility (GSI), which enables pistils to reject self-pollen by suppressing pollen tube elongation. In other plant species with S-RNase-based GSI, it has been shown that this suppression consists of two steps: first, slowing down of pollen tube elongation in the middle part of the style and second, complete arrest involving programmed cell death. To characterize the suppression pattern of incompatible pollen tubes in Prunus, we observed pollen tube elongation of ‘Satonishiki’ sweet cherry (Prunus avium) in ‘Satonishiki’ and ‘Rainier’ pistils on agar plates and ‘Satonishiki’ and ‘Rainier’ pollen tube growth in pistils on ‘Satonishiki’ cut branches. Incompatible selfed pollen tubes delayed penetration into the stigma in both experiments. Observation of pollen tubes in pistils on agar plates was difficult 24 h after pollination (HAP) due to wilting of the styles, while observing them on cut branches was possible up to 72 HAP. In the pistils on cut branches, ‘Satonishiki’ pollen tubes barely elongated in self pistils from 32 to 48 HAP when compatible ‘Rainier’ pollen tubes reached the base of a style, but resumed growth after 48 HAP and reached the base of the style. An RNase activity staining indicated that S-RNase was inactive 48 HAP. Finally, we observed pollen tube elongation in the style-grafted pistils on the cut branches. ‘Satonishiki’ pollen tube elongation was accelerated when the upper one-third of the self-pollinated styles was grafted onto compatible ‘Taishonishiki’ pistils. These results indicated that the suppression of incompatible pollen tube elongation in P. avium was consistently reversible. We discuss the suppression mechanism of incompatible pollen tube growth and the possibility of artificial control of Prunus self-incompatibility.

To elucidate the inhibitory effect of ethephon on the occurrence of water-soaked disorder in Japanese pear ‘Akizuki’ (Pyrus pyrifolia Nakai) fruit, we sprayed fruits with 100 mg·L⁻¹ ethephon solution approximately 120 DAFB in the 2012, 2014, 2015, 2016, and 2017 seasons. Ethephon treatment reduced the incidence and degree of water-soaked disorder at commercial harvest time. There was no significant difference in fruit size or soluble solids content between the ethephon-treated fruits and the control fruits, except for fruit size in the 2012 season. During the nine-day storage period after harvest, water-soaked disorder did not develop in either the ethephon-treated fruits or the control fruits. In addition, flesh firmness and soluble solids content did not differ between the ethephon-treated fruits and the control fruits during the storage period. Ethylene production increased sharply in the ethephon-treated fruits a few days after the ethephon treatment, in contrast to the control fruits. Sucrose content in the ethephon-treated fruits was higher than that in the control fruits on day 10 after treatment. Sorbitol content in the ethephon-treated fruits was lower than that in the control fruits on days 10 and 20 after treatment. Water-soluble, Na₂CO₃-soluble, and total pectin contents were not affected by the ethephon treatment. Hemicellulose, cellulose, and starch contents in the ethephon-treated fruits decreased earlier than those in the control fruits. Sucrose content was lower, but sorbitol and glucose contents were higher, in water-soaked tissue than in sound tissue. These results suggest that ethephon treatment rapidly induces changes in the contents of fruit’s internal components and accelerates fruit maturation, thereby alleviating factors that cause water-soaked disorder in ‘Akizuki’.

The sweet potato is a highly important crop in terms of food security worldwide, its nutraceutical properties have increased demand, generating new market opportunities. The availability of disease-free planting material ensures success in establishing this crop, achieving higher yield and better quality. This study aimed to improve the production system of high-quality planting material in greenhouse conditions through the evaluation of three mixtures of substrates based on peat, vermicompost, rice husk, and coconut substrate in different proportions; the best treatment was subsequently evaluated in the acclimatization process of in vitro plants. The substrates were characterized physicochemically and their effect on growth parameters in sweet potato seedlings was determined. For the acclimatization process of in vitro plants, the best mixture of substrates and a humid chamber during the first eight days of growth was compared to the conventional technique. A substrate composed of peat, vermicompost, and rice husk (3:1:1) resulted in the best seedling development. The proposed in vitro plant acclimatization strategy produced seedlings with good growth, high survival rates (92%), and a good multiplication rate (3.53) compared to the conventional strategy (peat without a humid chamber). The use of an optimal substrate and the incorporation of a humid chamber during the first days of growth guaranteed adequate ranges of temperature and relative humidity that kept the vapor pressure deficit of the leaves below critical levels (< 1.2 kPa). Increased efficiency in the production of high-quality planting material with carefully controlled phytosanitary conditions can make an important contribution to improving global disease management strategies in sweet potato cultivation.

This study investigated the role of dry matter (DM) and adhesiveness (or stickiness) and their relationship with the physicochemical and antioxidant properties of raw and steamed pumpkins. Through path analysis, raw pumpkin with a high DM value yielded a positive correlation with total flavonoid contents (TFC) and Ferric Reducing Antioxidant Power (FRAP) value in its raw form, and contained high total soluble solids and 2,2-diphenyl-2-picryl-hydrazyl (DPPH) activity in its steamed form. DM showed a correlation with total phenolic compounds (TPC) and DPPH activity. A sticky pulp generated high DM, TPC, TFC, and antioxidant capacity. The TPC and TFC were positively correlated with the antioxidant capacity. There was no relationship between cell structure, and starch granule characteristics of the raw pulp and cooked DM or stickiness. Therefore, DM and stickiness may be used as quality indicators of chemical contents and antioxidant capacity in pumpkin and could support pumpkin improvement programs.

Intumescence injury is a physiological disorder characterized by abnormal outgrowth of epidermal and parenchymal cells on the adaxial and/or abaxial surfaces of leaves. The purpose of this study was to examine cultivar differences in the incidence of intumescence injury, the relation between different calcium (Ca) conditions and intumescence injury, and to investigate countermeasures against intumescence injury in tomatoes. We grew tomato plants under different Ca nutrient conditions and treated them under high relative humidity and low ultra-violet light conditions to investigate intumescence injury incidence. The degree of intumescence injury varied among different tomato cultivars under a normal Ca condition with 4.5 me·L⁻¹ of Ca. Intumescence occurred in cultivars that showed no injury incidence under the normal Ca condition when they were grown with a low Ca nutrient solution containing 0.5 or 2.5 me·L⁻¹ of Ca. Intumescence injury incidence decreased in cultivars that showed high incidence under the normal Ca condition when they were grown with a high Ca nutrient solution containing 9.5 or 24.5 me·L⁻¹ of Ca. The differences in the incidence of intumescence among cultivars was marked with different Ca nutrient solution concentrations. There was a negative correlation between the degree of intumescence injury and the Ca content in tomato shoots. Foliar spraying with Ca was found to reduce the incidence of intumescence injury. It was suggested that intumescence injury in tomatoes can be mitigated by using cultivars in which intumescence is less likely to occur, increasing the Ca concentration of shoots by providing more Ca nutrients to the plant, and spraying Ca solution directly on the leaves.

Although a strong floral scent is typical of hybrid lilies, Asiatic hybrid lilies (Lilium spp.) have only a weak scent. Therefore, developing new cultivars with pleasant floral scents is an important objective in Asiatic hybrid lily breeding programs. Among the wild species contributing to Asiatic hybrid lily establishment, L. cernuum has a characteristic scent that the nose can perceive. We crossed Asiatic hybrid lily cultivars twice with L. cernuum to introduce floral scent traits into Asiatic hybrid lilies, and scent emission in the F₁ plants and their progeny lines was evaluated instrumentally. Flowers of L. cernuum emitted benzenoids/phenylpropanoids (mainly 2-phenylethanol and benzaldehyde), monoterpenes (predominantly linalool and linalool oxides), and a fatty acid (iso-valeric acid). Lilium cernuum gave off unpleasant odors mainly because of iso-valeric acid emission. The F₁ flowers also emitted these three chemical classes. Among the lines derived from the crosses between Asiatic hybrid lily cultivars and the F₁ plant, lines that emitted all three chemical classes and lines that released one or two of the three chemical classes were segregated, and some lines emitted benzenoids/phenylpropanoids or terpenoids without emitting fatty acids. We successfully selected elite breeding lines that predominantly emitted pleasant scents. Therefore, this study demonstrated the introduction of pleasant scent production capability into Asiatic hybrid lilies using interspecific hybridization with L. cernuum.

There are light-yellow flower cultivars of sweet pea (Lathyrus odoratus L.), but no deep-yellow ones. Observation of sweet pea flowers under ultraviolet and blue light suggested that carotenoids are responsible for the light-yellow coloration. We carried out both spectroscopic and high-performance liquid chromatography (HPLC) analyses of floral extracts of a light-yellow cultivar, ‘Artemis’, and revealed that the responsible pigments are not flavonoids, but carotenoids, among which acylated lutein is a major component. Because lutein is the pigment responsible for the deep-yellow color of flowers in other plants, we expect to be able to generate deep-yellow flower cultivars of sweet pea. The R and C loci are complementary genes regulating biosynthesis of anthocyanin pigments responsible for the cyanic coloration in sweet pea flowers. In progenies obtained by crossing ‘Artemis’ and a white cultivar, ‘Diana White’, whose genotype is RRcc, the F₁ plants had a red flower phenotype only, and the F₂ plants had four coloration phenotypes that were white, yellow, red and a combination of yellow and red. Furthermore, the F₁ plants, obtained by crossing ‘Artemis’ and another yellow cultivar, ‘Stella’, had a combination of yellow and red flower phenotype only. These data indicate that the genotype of ‘Artemis’ is rrCC and the yellow coloration trait is regulated by a single recessive gene, y, and furthermore, that the y gene is not in linkage with the R or C allele. The theoretical segregation ratio of the F₂ plants’ phenotypes obtained by crossing ‘Artemis’ as one parent in the case that Y, R and C loci are independent of each other are presented. We also found some cyanic color cultivars containing higher amounts of carotenoids than ‘Artemis’.

Generally, Asteraceae flowers such as chrysanthemums and gerberas, are low ethylene-sensitive and do not exhibit petal wilting and abscission. However, previous research found that the flowers of dahlia, an Asteraceae member belonging to the tribe Coreopsideae, are ethylene-sensitive and show abscission layer development in petal-ovary boundaries. In this study, we investigated the ethylene sensitivity of 17 ornamental Asteraceae species belonging to different tribes by measuring the petal drawing resistance and vase life after 1–3 μL·L⁻¹ ethylene exposure for 20 h. Although more than half of the tested species did not respond to ethylene, several species showed ethylene-sensitive petal wilting and abscission of fresh ray florets. Ethylene-sensitive petal wilting occurred in only two species (Calendula officinalis L. and Osteospermum L.) of the tribe Calenduleae, while ethylene-sensitive petal abscission occurred mainly in six species (Bidens ferulifolia D.C., Coreopsis lanceolata L., Cosmos atrosanguineus (Hook) Voss., Cosmos bipinnatus Cav., Cosmos sulphureus Cav. and Dahlia Cav.) of tribe Coreopsideae and one species (Helianthus annuus L.) of the tribe Heliantheae. In these species, abscission petals maintained their turgidity, and this process could be detected by measuring the petal drawing resistance of the ray florets. The reduction in petal drawing resistance, associated with abscission layer development in the petal-ovary boundaries, was observed only in these ethylene-sensitive species. The results of this study suggest that the ethylene sensitivity and petal senescing patterns in Asteraceae flowers may be associated with the phylogenetic classification at the tribe level.