Pear (Pyrus spp.) is one of the most important edible fruits belonging to the family Rosaceae. DNA markers, molecular genetics and genomics, and molecular breeding of pear have greatly progressed over the last few decades. The development of reliable DNA markers, such as simple sequence repeats and single nucleotide polymorphisms, has allowed DNA profiling of pear accessions, assessment of the genetic diversity within pear species, and analyses of phylogenetic relationships among pear species. Reference genetic linkage maps and genome-wide molecular markers have enabled practical marker-assisted selection for resistance to black spot and/or pear scab diseases, self-compatibility, harvest time, and fruit skin color in Japanese pear breeding programs. Molecular breeding has been shown to more than triple the selection efficiency of practical breeding compared with conventional breeding. Furthermore, breeding programs using two novel genomics-based approaches—genome-wide association studies and genomic selection—focusing on fruit quality and texture, and quantitative traits for breeding, are in progress. Co-linearity and functional synteny have been identified between pear and apple (Malus × domestica Borkh), and have been used to efficiently predict the function of a gene of interest and develop selection markers in related species.
The aim of the present study was to clarify the interaction between ethylene and abscisic acid (ABA) and maturation in highbush blueberry. We investigated the berry quality, ethylene evolution, and ABA concentration of berries treated with ethephon, an ethylene-generating compound; aminoethoxyvinylglycine (AVG), an ethylene synthesis inhibitor; ABA; and nordihydroguaiaretic acid (NDGA), an ABA synthesis inhibitor, before the onset of maturation in the highbush blueberry ‘Jersey’. The harvest time and the increasing time of ethylene evolution and ABA concentration in berries were earlier in 200 mg·L−1 ethephon treatment than in the control. Treatment of 30 mg·L−1 ABA progressed the time of increased ABA concentration but had little effect on the harvest time or ethylene evolution. AVG treatment at 150 mg·L−1 delayed the harvest time accompanied by decreasing the peak value of ethylene evolution and delaying the time of increased ABA concentration. Treatment of 300 mg·L−1 NDGA decreased the peak value of the ABA concentration, while it did not affect the harvesting time or ethylene evolution. These results suggest that ethylene, not ABA, induced maturation of blueberry at the mature green stage, and that ethylene was more closely involved than ABA with the progress of the whole maturation process.
Pitaya (Hylocereus spp.) is a tropical fruit grown in Okinawa prefecture, Japan. In this study, we developed simple sequence repeat (SSR) markers to assess the genetic diversity of pitaya accessions collected in Okinawa prefecture. SSR markers were developed with next-generation sequencing, using the Roche 454 GS FLX+ platform. Seventy primer sets were tested for the genetic identification of pitaya, including 50 AG motif and 20 AC motif SSRs. In total, 16 SSR markers successfully amplified fragments and exhibited polymorphism among the accessions. The SSR markers revealed the genetic diversity parameters including number of alleles per locus (ranging from 6 to 12), expected heterozygosity (ranging from 0.5 to 0.85), observed heterozygosity (ranging from 0.23 to 0.93), polymorphic information content (ranging from 0.47 to 0.83), fixation index value (0.013), and out-crossing rate (0.973). Using these SSR markers, genetic identification was performed for 32 pitaya accessions collected in Okinawa prefecture. These accessions could be distinguished genetically using three SSR markers, with the exception of accessions between ‘Uruma White’/‘Nago White’ and ‘Ohgimi Red 1’/‘Ohgimi Red 2’. Genetic diversity analyses suggested six groups, and grouping appeared to be based on differences in species. The obtained SSR markers and clarified genetic background information may facilitate future breeding of pitaya.
The production of yellow-skinned apples has increased in recent years; however, they are less acceptable to consumers than red-skinned apples. Therefore, the production of high-quality fruit is essential. In the present study, we applied a girdling treatment at 1) different times (June or August), and 2) different widths (2 cm, 5 cm, and 8 cm). We compared the effect on tree growth, flower bud formation and fruit quality over a 4-year field trial using vigorous yellow-skinned ‘Koukou’ apple trees. The August girdling reduced the shoot growth by about 6 to 10 cm per shoot and this reduction also restricted secondary extension of the shoots. The August treatment improved the fruit quality parameters, including the soluble solids content and skin color index, more effectively than the June treatment. Compared with the girdling timing, the effect of girdling widths in August was less obvious, but even the 2 cm treatment in August was enough to reduce tree vigor and improve fruit quality. Apical flower bud formation was accelerated by the August girdling in both the treatment year and the following year. Regardless of the girdling width, the August girdling improved the fruit quality parameters: e.g. flesh firmness, soluble solids content, and skin color index. The August girding fruit also had higher sorbitol and sucrose concentrations than the control. Moreover, both the girdling treatments accelerated the incidence of watercore, which is a preferred condition for the Asian market. In conclusion, we found that all widths of girdling in August improved the harvested fruit qualities, including the sugar (sucrose) content, as well as watercore development in the treatment year and effectively controlled tree vigor, increased flower bud formation and increased yields.
The emergence of flowering disorder, specifically the bud break disorder observed in flower buds, has become a serious problem for Japanese pear ‘Kosui’ greenhouse production in southern Japan. To understand the mechanism behind this problem, the expression of genes related to endodormancy and flowering were investigated in “flowering disorder trees” (FDTs). In 2017 and 2019, remarkably warm temperatures were recorded during the winter season, and the degree of flowering disorder in FDTs was severe. Forced cultivation experiments suggested that endodormancy of “normal trees” (NTs) was released well before fulfilling the chilling requirement (CR), suggesting that ‘Kosui’ trees grown in greenhouses had a short endodormancy period. We also found that the dormancy depth of FDTs was shallower than that of NTs before and after fulfilling the CR, whereas FDTs entered a deeper dormancy when the greenhouse was covered by a plastic film during the ecodormancy period, suggesting that FDTs’ dormancy progression was significantly different from that of NTs during endodormancy and ecodormancy. Gene expression analysis showed that the expression level of the endodormancy-related gene, MADS13-3, was correlated with dormancy depth in NTs, but not in FDTs. Additionally, the expression levels of the putative flowering regulator, PpFLC3-like gene, were significantly lower in FDTs than in NTs in December, before fulfilling the CR. Additionally, the flowering promoter, PpFT, was also significantly lower in FDTs than in NTs in March after fulfilling the CR. The survey years 2017 and 2019 were warm winters with a high mean temperature difference from the climatological normal in December. These results suggest that the flowering disorder of greenhouse-cultivated ‘Kosui’ is related to the shallow dormancy depth and/or inappropriate dormancy and flowering progression during endodormancy and ecodormancy, especially when flower buds encounter high temperatures during dormancy.
The pungency-variable sweet chili pepper ‘Shishito’ (Capsicum annuum) is widely cultivated in Japan. While ‘Shishito’ is generally used as a vegetable because of its relatively low pungency, it sometimes exhibits high pungency depending on cultivation conditions. Although the occurrence of pungent ‘Shishito’ fruits is a problem in retail distribution and utilization, the responsible mechanism is largely unknown. As one approach to clarify the mechanism, we focused on the effects of parthenocarpy (resulting in seedless fruit) on the pungency traits of ‘Shishito’ fruits. In the present study, artificial parthenocarpic ‘Shishito’ fruits were prepared by treatment with 2,4-dichlorophenoxyacetic acid (2,4-D), and the pungency level was investigated by quantification of capsaicinoids, components responsible for the pungency. For comparison, two controls were used: naturally pollinated fruits and 2,4-D-treated pollinated fruits which were exposed to 2,4-D treatment without parthenocarpy. The results indicated that the capsaicinoid content in parthenocarpic fruits tended to be higher compared to the controls. This suggests that the alterations in pungency in ‘Shishito’ were associated with parthenocarpy. Further, these relationships were assessed using a molecular method, and gene expression analysis using qRT-PCR was conducted on 16 capsaicinoid biosynthesis genes. The results showed that eight capsaicinoid biosynthesis genes (Pun1, pAMT, KAS, CaMYB31, BCAT, CaKR1, ACL, and FAT) exhibited parthenocarpy-specific high expression, suggesting that these genes influence capsaicinoid biosynthesis and the pungency levels in parthenocarpic fruits. This is a novel report that carefully investigated the parthenocarpy-dependent changes in the pungency traits of chili pepper. We anticipate that the data will add to horticultural knowledge and help control the pungency of ‘Shishito’ fruits during cultivation.
Environmental factors influence the contents of taste components, such as capsaicinoid compounds, in the fruit of chili pepper (Capsicum annuum). The present research was conducted to evaluate the effect of water supply and harvesting date after flowering on sugar and capsaicinoid contents in fruit of the Japanese chili pepper cultivars ‘Botankosho’, ‘Fushimiamanaga’, ‘Manganji’, and ‘Sapporo Oonaga Nanban’. The experiment was conducted in a greenhouse from April to October in 2016 and 2017. Three water supply treatments were applied: 260 mL (excess), 130 mL (standard), and 50 mL (drought) per application. Fruit were harvested at 20, 30, 40, and 50 days after flowering (DAF). Glucose, glutamic acid, and total sugar were measured using a portable spectrophotometer, and capsaicinoid content was measured by HPLC. Total sugar content and Brix tended to increase with later harvesting, whereas glucose content did not change significantly by DAF. Sugars in the fruit were dominated by fructose, and the ratio of fructose content to total sugar content increased as the fruit matured. Glutamic acid content in the fruit increased up to 40 DAF, and thereafter remained unchanged or decreased. The capsaicinoid content of the fruit increased with fruit maturation. Elevation in water supply induced an increase in the fruit glucose content and decrease in total sugar and glutamic acid contents. Previous studies of tomato (Solanum lycopersicum L.) found that total sugar and glucose contents decrease in response to increase in water supply. Therefore, it is suggested that sugar metabolism and accumulation differ in the fruits of tomato and chili pepper. The highest capsaicinoid content in chili pepper fruit was observed in response to the drought treatment.
Parthenocarpy is a trait in which fruit set and development are induced without fertilization, thereby contributing to labor saving in fruit production. In Cucurbita species, parthenocarpic cultivars have been reported in Cucurbita pepo, but not in Cucurbita maxima and Cucurbita moschata. In this regard, the identification of parthenocarpic cultivars and clarification of their characteristics will contribute greatly to the research and breeding of the parthenocarpic trait in Cucurbita species. In this study, we aimed to genetically screen diverse Cucurbita accessions for high parthenocarpic ability and to elucidate the characteristics of the parthenocarpic cultivars discovered by the screening. We screened 33 accessions from squash genetic resources and found that a Cucurbita moschata cultivar, ‘Miyazaki-wase No. 1’, exhibited parthenocarpy. In order to clarify the characteristics, we examined the fruit set rate, fruit expansion, and fruit quality of ‘Miyazaki-wase No. 1’. In the spring and fall experiments, the fruit set rate of parthenocarpic fruit was lower than that of pollinated fruit. On the other hand, there was no significant difference in the transverse diameter and weight of parthenocarpic and pollinated fruits at harvest. These results indicated that the fruit set ability of parthenocarpic fruit is inferior to that of pollinated fruit, although the fruit expansion ability of parthenocarpic fruit was almost the same as that of pollinated fruit. In addition, we compared the composition of parthenocarpic fruit with that of pollinated fruit at harvest and after storage in the fall experiment. The results demonstrated that there was no significant difference in all the examined compositions between the parthenocarpic and pollinated fruits at harvest. On the other hand, the β-carotene concentration of parthenocarpic fruit was significantly lower than that of pollinated fruit one month and two months after harvest. These results indicated that parthenocarpic fruit development did not affect fruit quality at harvest, but had an effect on β-carotene metabolism during storage. We showed that ‘Miyazaki-wase No. 1’ is a parthenocarpic cultivar and clarified its characteristics. Based on the results, progress in research and breeding of parthenocarpic cultivars in Cucurbita species is anticipated in the future.
The demand for broccoli (Brassica oleracea L. var. italica) is rapidly growing in Japan, and a new production system to increase broccoli yield is required. During processing, broccoli florets are separated from the head, and floret yield may be increased by enlargement of heads beyond existing retail standards. Therefore, we conducted four cultivation tests over two years and investigated floret yields of 10 cultivars during spring and autumn cropping. We sought to identify high-yielding cultivars when the heads are enlarged via either an extension of the cultivation period or sparse planting. In the control plots, the broccoli heads were harvested at approximately 12 cm in diameter, following normal retail standards. In the extended plots, the cultivation period was extended to the limits of marketable quality. The plant density of these two plots was 3,125 plants per 10 a. In the sparse plots, plant density was half of the other plots, 1,563 plants per 10 a, and the heads were enlarged and harvested as in the extended plots. The floret yield of the control plots was 560–958 kg/10 a, and the floret yield of the extended plots was 905–2,504 kg/10 a. Head diameter of the extended plots was 15–21 cm. In the sparse plots, head diameter was 15–25 cm, and the fresh weight of the florets tended to increase, but floret yield was only 657–1,870 kg/10 a, due to the half number of plants. Across seasons and years, the ‘Grandome’ cultivar had consistently high yields, suggesting that it is suitable for enlarged harvesting. Compared to the ‘Pixel’ cultivar, the photoassimilates of ‘Grandome’ were more concentrated in the main shoot due to the fewer side shoots. Moreover, there were several immature floral shoots in the head of ‘Grandome’ at 12 cm diameter, which may explain the large size. The harvest index also increased with broccoli head size, so the large head production system enabled more efficient production and increased floret yield compared to conventional cropping methods.
Matthiola incana is a popular winter-flowering plant, and white is considered a valuable flower color for marketed cultivars. In this study, we aimed to identify the genes responsible for white flower coloration in six commercial cultivars of M. incana used as cut and potted flowers. The expression levels of chalcone synthase, flavanone 3-hydroxylase, flavonoid 3'-hydroxylase, dihydroflavonol 4-reductase, anthocyanidin synthase (ANS), and anthocyanidin 3-O-glucosyltransferase in the petals of ‘Kiss me White’ and ‘Pygmy White’ were 0%–48% lower than those in the purple flower ‘Vintage Lavender’, whereas the expression level of basic helix-loop-helix 2 (bHLH2) was two-fold higher. Significantly reduced expression levels of ANS were also detected in four other white flower cultivars: ‘Vintage White’, ‘Iron White’, ‘White Wonder No. 2’, and ‘Quartet White’. All investigated white flower cultivars had a single nucleotide deletion in the first exon of ANS, which we designated as ans-1. This generates a frameshift mutation and a nonsense codon. In addition to ans-1, ‘Kiss me White’ and ‘Pygmy White’ have a 481-bp insertion within bHLH2. This insertion has features of hAT-type transposable elements and was designated as dTmi1. All white flower cultivars contain the ans-1 mutation, whereas ‘Kiss me White’ and ‘Pygmy White’ are double mutants containing both bhlh2dTmi1 and ans-1. ‘Kiss me Yellow’, which accumulates carotenoids, but not anthocyanins, in its petals possesses the bhlh2dTmi1 allele, but not the ans-1 allele. Therefore, either bhlh2dTmi1 alone or ans-1 alone can lead to a deficiency in anthocyanin production in commercial cultivars of M. incana. We also developed co-dominant DNA markers that can distinguish between wild-type and mutant alleles of both bHLH2 and ANS. In combination with other previously developed markers that can distinguish between single- and double-flowered individuals, these markers will be useful for nursery plant management and breeding of commercial M. incana.
Portulaca umbraticola, an important ephemeral summer bedding plant, may be a model system for studies on flowering behavior under heat stress. Herein, we report the first comprehensive transcriptome analysis of P. umbraticola by RNA-sequencing. We generated 22.15 G bases which were assembled into 68,928 unigenes, and a total of 43,880 coding sequences (CDS) were detected. We also detected 13,603 simple sequence repeats on 10,784 unigenes, and predicted 1,444 transcription factor (TF) coding unigenes. Subsequently, we focused on gene discovery in the areas of flower senescence and opening rhythm. We identified the majority of transcripts involved in ethylene biosynthesis, perception, and signaling pathways, as well as transcripts corresponding to circadian clock components. Expression profiles of the ethylene biosynthesis and signaling pathway genes in two cultivars with different flower longevity showed a clear correlation with previously observed endogenous ethylene production. PuACS1 and PuACO2 transcripts showed higher expression, and peaked earlier in a short lived cultivar than in a long lived cultivar. Expression analysis of the core clock component genes showed PuCCA1/PuLHY and PuTOC1 under reciprocal circadian regulation similar to that found in Arabidopsis thaliana, and other plant species. This study provides the first steps in understanding the molecular mechanisms underlying flowering traits in P. umbraticola, and paves the way for future integrated insights into molecular genetics, biotechnology and physiological studies of P. umbraticola.
In order to solve the problems of commercial orchid growers, who need to force Vanda flowering for both blooming on demand and uniformity, an appropriate environment to control flower development is a key factor. However, little research has been conducted on this topic. This research aimed to determine the effects of short day cycles on the flowering of Vanda ‘Manuvadee’, which usually has high productivity from September to February. Plants were grown under seven hour day lengths for three, six, and nine weeks before being moved to natural day length (approximately 12 hours/day), and then compared with plants cultivated only under a natural day length condition (control). All flowers were grown in an environment of 25 ± 2°C, 70–80% relative humidity. 21-21-21 (N-P2O5-K2O) fertilizer was sprayed weekly at an average of 0.44 g per plant. Results showed that forcing under seven hour day lengths for six and nine weeks could on average delay flowering to 22 and 38 days later than the control treatment, respectively. Forced plants had 100% of first flower opening within 55 days, while the control treatment group gradually opened and took approximately 101 days to anthesis. The nine-week short day treatment provided the most inflorescences, and better longevity was obtained with the six and nine-week short day treatments. Short day cycles decreased TNC concentration in leaves, but did not affect C/N balance at the ninth week; however, P and K concentrations increased.
The putative parents of the Hirado azalea (Rhododendron × pulchrum) are R. scabrum, R. ripense, R. × mucronatum, and other related cultivars. Hirado azalea shows a wide range of flower color variation, but the genetic basis for this color variation is not well understood. In this study, we investigated the anthocyanin pathway gene, flavonoid 3', 5' hydroxylase (F3'5'H), by genomic DNA analysis, cDNA sequence analysis, and deduced amino acid sequences to assess the genetic relationships between these taxa, as well as investigating the genetic basis of color variation in this group. In R. scabrum and red and pink flowered Hirado azalea cultivars, in which delphinidin (Dp) derivatives are absent, only the exon 2 region was amplified using specific primers in a coding region (CDS) of the F3'5'H gene, except for exon 1, suggesting that the DNA structure of exon 1 is defective in these plants that lack Dp derivatives. On the other hand, R. ripense, R. macrosepalum, and R. yedoense var. poukhanense and R. × mucronatum ‘Shiro-ryūkyū’, with Dp derivatives have normal F3'5'H DNA gene structure. The lengths of the F3'5'H cDNA nucleotide sequences of these wild species were 1533 bp (510 AA), whereas in R. × mucronatum ‘Shiro-ryūkyū’, two different sequence lengths were observed—1533 and 1551 bp (510 and 516 AA). R. ripense, R. × mucronatum ‘Shiro-ryūkyū’, and four purple and white flowered Hirado azalea cultivars were grouped in the same cluster in the F3'5'H gene phylogeny. Among the four Hirado azalea cultivars, the lengths of F3'5'H in CDS were 1551 bp, which included a 5 bp insertion adjacent to the stop codon in ‘Ademurasaki’ and ‘Hakuhō’. However, ‘Hirado-no-homare’ and ‘Shirokujyaku’ lacked this insertion and had 1533 bp CDS. When PCR was performed to distinguish the 5 bp insertion, the amplified product was found in some R. ripense individuals and R. × mucronatum ‘Shiro-ryūkyū’, but not in R. scabrum or R. macrosepalum. These results suggest that the wide range of flower color in Hirado azalea cultivars is caused by variation in the F3'5'H genotype derived from hybridization between R. scabrum and either R. ripense or R. × mucronatum ‘Shiro-ryūkyū’.
Crown gall disease caused by Agrobacterium tumefaciens causes economic loss in ornamental production in Japan. To breed a resistant rootstock, we used crown gall resistant Rosa ‘PEKcougel’ to hybridized with tetraploid of R. multiflora ‘Matsushima No. 3’. In this study, we investigated the crown gall resistance characteristics in their progenies. In the needle prick test, eight tested progenies showed significantly smaller wounds than R. ‘PEKcougel’. In the stem segment culture and opine assay, six progenies formed no callus tissue while three progenies formed calluses and had no opine detected. Further oncogene expression analysis was performed to evaluate crown gall disease resistance, since the low callus formation rate limited the application of opine assay. In the oncogene expression analysis, some progenies of tetraploid of R. multiflora ‘Matsushima No. 3’ showed a lower expression level of both ipt and iaaM than R. ‘PEKcougel’. Furthermore, ipt expression had a significant positive relationship with tumor size. Taken together, these results suggest that ipt expression analysis can be used for evaluating crown gall disease resistance in rose progenies. Furthermore, eight progenies with strong crown gall disease resistance were confirmed.
Reconstruction of cell wall polysaccharide is necessary for fruit development and ripening. Arabinose is the one of neutral sugars constituting wall polysaccharides and arabinose-containing polysaccharides play an important role in cellular attachment. In this study, expression patterns of α-l-arabinofuranosidase genes were examined in three tomato cultivars, the processing type ‘OSKAR’, fresh market type ‘Ailsa Craig’, and their hybrid ‘Shonan Pomoron Red’, to elucidate the function of α-l-arabinofuranosidase in fruit traits such as shape, growth, firmness, and juiciness. While there was no significant difference in fruit diameter among the cultivars, longitudinal elongation was observed in ‘OSKAR’ with increasing fruit weight. The hybrid ‘Shonan Pomoron Red’ showed intermediate longitudinal growth. Compared to ‘OSKAR’ at the red ripe stage, fruit flesh softened more in ‘Ailsa Craig’ and much water was released from the pericarp disk. The rate of water release in ‘Shonan Pomoron Red’ was intermediate. The α-l-arabinofuranosidase genes, SlArf/Xyl2, LeXYL1 and LeXYL2, were highly expressed in the young fruits and SlArf/Xyl1 and LeXYL1 were up-regulated when ripening initiated. However, their expression levels did not appear to cause the difference in fruit traits such as growth rate, fruit shape, and firmness among the cultivars. On the other hand, expression levels of SlArf/Xyl1, LeARF1 and LeXYL2 were consistent with the rate of water release from ripe fruit. Therefore, α-l-arabinofuranosidase could influence fruit flesh texture and juiciness in fresh market and processing cultivars.