Japanese pear (Pyrus pyrifolia Nakai) is an important Rosaceous fruit tree in Japan. This species exhibits gametophytic self-incompatibility (GSI), which is controlled by a single S-locus with multiple S-haplotypes. Although GSI is a genetic mechanism to prevent inbreeding and promote outcrossing to maintain genetic diversity, it can be problematic in fruit trees because it causes unstable fruit set. Therefore, orchardists interplant Japanese pear with other lines as pollinizers or conduct artificial pollination to ensure fruit set. To achieve stable fruit production and to reduce or eliminate the need for artificial pollination, research on the GSI of Japanese pear has been conducted by pollination experiments and by characterization of self-compatible (SC) mutants. Additionally, breeding programs have progressed to produce SC cultivars with high fruit quality. Recently, molecular analyses of GSI and SC mutants in Japanese pear have provided new information that is relevant to the stable fruit production and efficient breeding of Japanese pear. This review focuses on studies of the GSI of Japanese pear, and especially on the recent development of DNA markers for S-genotyping and marker-assisted selection of SC trees. In addition, the candidate genes controlling pollen S specificity and a model of the molecular mechanism of GSI in Japanese pear are described.
Seawater was applied to pot-grown citrus trees, namely, 2 cultivars of satsuma mandarin (Citrus unshiu Marcow.) and ‘Miyauchi-iyokan’ (Citrus iyo hort. ex Tanaka), to clarify the feasibility of salt stress to improve fruit quality and its physiological mechanism. The applications of undiluted seawater (1X) and half-strength-diluted seawater (1/2X) significantly increased soil electrical conductivity (EC) and decreased leaf water potential to different degrees compared with those in the control. The effect of seawater concentration on leaf water potential was more obvious when it was determined at predawn than at noon. Only a slight increase of leaf Na content and no significant leaf abscission occurred in 1/2X compared with those in the control, while significant increases of these parameters were observed in 1X. Seawater irrigation inhibited fruit growth, but did not affect fruit shape and flesh ratio. Soluble solids content (SSC) in the juice was significantly higher upon the seawater applications at about 0.8 to 2°Brix depending on the cultivar than in the control; reducing sugars and/or sucrose were also increased by the salinity treatments in satsuma mandarin. Seawater treatments tended to delay the decrease of titratable acidity, but no significant difference between 1/2X and the control was detected at harvest. These results indicate that the mild salt exposure induced by 1/2X at the extent of 0.3 to 0.5 MPa lower water potential at predawn than that in the unstressed control could improve citrus fruit quality without injury. The results also suggest that salt stress by seawater irrigation would affect fruit quality through a similar physiological process, osmoregulation, to that of drought stress.
A series of investigations were conducted to identify an efficient cultivation method for producing uniform fruit in young ‘Hongro’ and ‘Fuji’ apple trees through vigor balance control and crop load adjustment at commercial orchards in Pocheon, South Korea, for two consecutive growth seasons (the third and fourth leafy years), namely, the years 2012 and 2013. There was a highly significant correlation between the cross-sectional area of the main stem (the trunk) and those of all the branches emerging from the main stem, with coefficients of 0.857** (P < 0.001) in ‘Hongro’ and 0.699** (P < 0.001) in ‘Fuji’. The vigor balance, defined as the ratio of branches to the main stem, was the most densely distributed in the range of 3.0 to 3.5 for diameter and around 1.2 for cross-sectional area in both varieties. The present study evaluated the level of crop load by measuring flower cluster density, crop density, and yield efficiency, and found the most densely distributed range was lower than the mean value. The apple trees showed higher productivity with a vigor balance of 1.1 to 1.3 in both varieties, but showed lower productivity with a vigor balance above 1.3 in ‘Hongro’ and below 1.1 in ‘Fuji’ trees in the third and fourth leafy years. Upon adjusting crop load by yield efficiency, the present study obtained higher productivity with a higher degree of yield efficiency in the two consecutive years. However, fruit size and other characteristics demonstrated little change by vigor balance control and crop load adjustment. The uniformity of fruit size and other characteristics was improved by the individual or combined application of vigor balance (from 1.1 to 1.3 in both varieties) and crop load adjustment (from 0.9 to 1.3 kg per cm2 TCA in ‘Hongro’ and from 0.7 to 1.1 kg per cm2 TCA in ‘Fuji’). Notably, the uniformity of fruit size and total soluble solids was efficiently improved by the application of crop load adjustment and vigor balance control, respectively.
Flavonoid biosynthesis in grape (Vitis spp.) berry skin is affected by environmental factors such as light and temperature. However, the components of the light signaling and low-temperature-induced abscisic acid (ABA) signaling networks related to flavonoid accumulation in grape berry skin have not been fully elucidated, and how environmental conditions affect these components remains unclear. To clarify the details of the possible light- and ABA-related signal transduction networks, we developed a grape oligo-DNA microarray (38,549 independent probes) using the publicly available genomic sequence of grape, and performed comprehensive transcriptome analysis using detached ‘Pione’ grape (Vitis labruscana × V. vinifera) berries cultured under different light and temperature conditions. Using the microarray data, we explored the light-inducible and low-temperature-inducible genes in post-veraison grape berries. We identified 40 light-inducible genes, 55 low-temperature-inducible genes, and 34 genes induced by light plus low temperature. Among these, we selected elongated hypocotyl 5 (HY5), open stomata 1 (OST1), and enhanced response to ABA 1 (ERA1) as candidate light-inducible, low-temperature-inducible, and light- plus low-temperature-inducible genes, respectively. We investigated their detailed expression characteristics in grape accessions by means of quantitative real-time polymerase chain reaction analyses, and hypothesized that HY5, OST1, and ERA1 might be involved in flavonoid biosynthesis via light signaling and low-temperature signaling networks. We also established an extensive catalog of gene expression patterns to support future investigations of other candidate genes that respond to light and temperature in grape berry skin.
Japanese pear (Pyrus pyrifolia Nakai) ‘Gold Nijisseiki’ fruit were stored for 28 days at 0, 4, 10, 15, or 22°C. The effects of storage temperature on sucrose metabolism and on the expression of genes for sucrose-metabolizing enzymes were investigated. Fruit firmness, skin color, and content of various sugars were affected by storage temperature. Fruit stored at 22°C underwent rapid fruit softening and skin color change. Fruit stored at 15 or 10°C had lower sucrose content and higher glucose and fructose content than those stored at 0, 4, or 22°C. To investigate whether sucrose loss is related to changes in the expression of sucrose-metabolizing enzymes (vacuolar acid invertase: AIV; and sucrose phosphate synthase: SPS), we examined the expression of 3 genes during storage, namely, those encoding AIV (PpAIV1 and PpAIV2) and SPS (PpSPS1). Storage at 10 and 15°C increased the expression of PpAIV2 within a week and that of PpAIV1 in 14 days, while storage at 0 and 4°C delayed increased expression of PpAIV1 and PpAIV2 until after 28 days. Changes in the gene expression of sucrose-metabolizing enzymes were followed by delayed responses in sugar content.
Flowering plants have developed a genetically determined self-incompatibility (SI) system to maintain genetic diversity within a species. The Solanaceae, the Rosaceae, and the Plantaginaceae have the S-RNase-based gametophytic SI (GSI) system, which uses S-RNase and F-box proteins as the pistil S and pollen S determinants, respectively. SI is associated with culture and breeding difficulties in rosaceous fruit trees, such as apple, pear, and stone fruit species; therefore, researchers in the pomology field have long studied the mechanism and genetics of SI in order to obtain clues to overcome these difficulties. Here, we investigated the evolutionary paths of the S-RNase genes by tracking their duplication patterns. Phylogenetic analysis and estimation of proxy ages for the establishment of S-RNase and its homologs in several rosaceous species showed that the divergence of S-RNase in the subtribe Malinae and the genus Prunus predated the gene in most recent common ancestors of Rosaceae species. Furthermore, the duplicated S-RNase-like genes were accompanied by duplicated pollen S-like F-box genes, suggesting segmental duplications of the S locus. Analysis of the expression patterns and evolutionary speeds of duplicated S-RNase-like genes in Prunus suggested that these genes have lost the SI recognition function, resulting in a single S locus. Furthermore, the S loci in the current Rosaceae species might have evolved independently from the duplicated S loci, which could explain the presence of genus-specific SI recognition mechanisms in the Rosaceae. The results of the present study should be valuable for the future development of artificial SI control and for self-compatible breeding in rosaceous horticultural plant species.
In Thailand, Dendrobium is the most popular crop grown for cut flowers and as a pot plant for local use and export. Some native species are used for hybrid production while some are specific to particular parts of the country and need to be conserved. The sequences of rDNA ITS (ITS1-5.8S-ITS2) and the matK gene were used to reconstruct the phylogenetic relationships of 27 native Dendrobium spp. in Thailand, which are composed of 9 sections: Breviflores, Callista, Dendrobium, Distichophyllum, Formosae, Pedilonum, Rhopalanthe, Stachyobium, and Strongyle. The average levels of nucleotide divergence (p-distances) of matK and rDNA ITS sequences were 1.3% and 11.2%, respectively. The topologies of the phylogenetic trees reconstructed based on matK and rDNA ITS sequences were slightly different. Use of the rDNA ITS sequence was shown to be a more authoritative systematic approach than use of the matK gene sequence in the genus Dendrobium. The result of the combined data (matK-rDNA ITS) was highly similar to the result from rDNA ITS. From rDNA ITS and combined data, the twenty-seven Dendrobium spp. were clearly grouped into two clades with some differences from the morphological classification. The present study provides the first molecular phylogeny of 27 native Dendrobium species in Thailand.
Species belonging to the Hydrangea genus, including Hydrangea macrophylla (Thunb.) Ser. and H. serrata (Thunb.) Ser., have inflorescences consisting of decorative and non-decorative flowers. The generation of double-flowered decorative flowers is an important objective for hydrangea breeders. This study aimed to elucidate the inheritance pattern of double flowers in H. macrophylla and H. serrata. Double-flowered progeny were obtained from three out of eleven crosses between double-flowered cultivars as the seed parent and single-flowered cultivars or lines as the pollen parent. When double-flowered progeny were produced using three cross combinations, the progenitor of both double-flowered cultivars and single-flowered lines was the double-flowered cultivar ‘Jogasaki’. In progeny obtained from these crosses, the segregation ratio of double- and single-flowered types was 1:1. Conversely, all progeny obtained from a cross in which the double-flowered cultivar as the seed parent differed from the seed parent of the single-flowered line as the pollen parent bore single flowers, and double-flowered progeny were not produced. Double-flowered progeny were obtained in two out of four crosses among the single-flowered lines; the segregation ratio of double- and single-flowered types was 1:3. The single-flowered lines shared the same seed parents, ‘Jogasaki’ or ‘Sumidanohanabi’. These results indicate that the double-flowered phenotype of decorative hydrangea flowers may be a recessive characteristic controlled by a single major gene. In addition, these results indicate that double-flowered progeny can be obtained when a pair of recessive genes are identical.
Two types of floral morph, called thrum and pin, occur in heterostylous species. The thrum and pin flowers have shorter and longer styles, respectively. Heterostyly in Linum has been studied since Darwin’s era. The floral morph, self-incompatibility, and related phenotypes have been well characterized using a natural population, but genetic analysis using a segregated population has not been reported, and the mode of inheritance of heterostyly in Linum remains to be investigated. We prepared a segregated population by crossing thrum and pin flowers of Linum grandiflorum Desf. and investigated style and stamen lengths. On the basis of the style to stamen length ratio, the population could be divided into thrum and pin clearly at a ratio of 1:1. Style length of pins was 1.6 times longer than that of thrums. To investigate the factor regulating the difference in style length, we further measured the style cell length of thrums and pins. The style cell length of pins was longer than that of thrums, whose rate was comparable to the rate of the style length ratio between thrum and pin flowers. These findings indicate that the floral morph of heterostyly in Linum is controlled by a single diallelic locus, and that a difference in the cell expansion rate caused thrum and pin morphs in the style, such as in a typical heterostylous species. PCR genotyping showed that TSS1, an S candidate gene reported previously, cosegregated completely with the thrum phenotype, indicating strong linkage between the S locus and TSS1. Furthermore, three flower colors (red, pink, and white) were observed at a 1:2:1 ratio, and no white thrum flowers or red pin flowers were found in this population. These flower color phenotypes could also be controlled by a diallelic locus, whose two alleles (R and r) would be incompletely dominant, and therefore, may be linked to the S locus.
This study was conducted to demonstrate the seasonal change of floral organ number and morphology, and the effect of growth temperature on floral morphology in double-flowered cyclamen with petaloid-stamens. In plants grown under seasonal variable temperature, floral organ number and morphology in petaloid-stamen type of double flower changed as time passed, but the degrees of such changes differed depending on the line; there were two types, namely, “variable” and “relatively stable”, in terms of the number of outer and inner petaloid-stamens throughout the flowering period. In the plants grown under different constant temperatures, the rate of complete petals (petaloid-stamens) to the total organs in whorl 3 was greatest at 15°C, followed by the values at 25°C and 20°C. In contrast to complete petals, the rate of incomplete petals (petaloid-stamens) to the total organs in whorl 3 was greatest at 20°C, followed by the values at 25°C and 15°C. The rate of stamen-like organs to the total organs in whorl 3 did not differ significantly among treatments, and the rate of stamens to the total organs in whorl 3 was suppressed only at 25°C. Although the total numbers of stamens and stamen-like organs were similar at 15°C and 20°C, the developed positions of stamen-like organs and stamens were significantly different between 15°C and 20°C. Additional organs including stamens were produced inside the petaloid-stamen at 15°C, while restoration of the stamen was induced at 20°C. In conclusion, floral morphology shows seasonal change, and growth temperature affects the petaloidy of stamen in double-flowered cyclamen. However, the effect on petaloidy differs according to the line.