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  • Author or Editor: Jianjun Chen x
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Deep transcriptome sequencing allows for the acquisition of large-scale microsatellite information, and it is especially useful for genetic diversity analysis and mapping in plants without reference genome sequences. In this study, a total of 14,004 simple sequence repeats (SSRs) were mined from 10,511 unigenes screening of 63,608 nonredundant transcriptome unigenes in loquat (Eriobotrya japonica) with a frequency of 22 SSR loci distributed over 100 unigenes. Dinucleotide and trinucleotide repeat SSRs were dominant, accounting for 20.62%, and 42.1% of the total, respectively. Seventy primer pairs were designed from partial SSRs and used for polymerase chain reaction (PCR) amplification. Of these primer pairs, 54 exhibited amplification and 33 were polymorphic. The number of alleles at these loci ranged from two to 17, and the polymorphism information content values ranged from 0.24 to 0.89. We tested the transferability of 33 SSR polymorphic primer pairs in apple and pear, and the transferability rates in these two species were 90.9% and 87.9%, respectively. A high level of marker polymorphism was observed in apple [Malus ×domestica (66.7%)], whereas a low level was observed in pear [Pyrus sp. (51.5%)]. In addition, the PCR products from seven SSR primer pairs were selected for sequence analysis, and 89.2% of the fragments were found to contain SSRs. SSR motifs were conserved among loquat, apple, and pear. According to our sequencing results for real SSR loci, ≈12,490 SSR loci were present in these loquat unigenes. The cluster dendrogram showed a distinct separation into different groups for these three species, indicating that these SSR markers were useful in the evaluation of genetic relationships and diversity between and within the species of Maloideae in the Rosaceae. The results of our identified SSRs should be useful for genetic linkage map construction, quantitative trait locus mapping, and molecular marker-assisted breeding of loquat and related species.

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Curcuma L. is an economically important genus in the family Zingiberaceae. Many species are grown as medicinal, culinary, and ornamental crops. As a result of their high morphological diversity and small chromosome sizes, chromosome numbers and species relationships of Chinese Curcumas remain debated. This study examined chromosome numbers of 15 populations representing 11 species of Curcuma from China. Results showed that only Curcuma flaviflora S. Q. Tong was diploid with 2n = 2x = 42 and C. kwangsiensis S. G. Lee & C. F. Liang was tetraploid with 2n = 4x = 84. The other species were triploid (2n = 3x = 63). The study indicated that the basic chromosome number of Curcuma from China could be x = 21. The diploid C. flaviflora produced viable seeds, which was the main means for propagation. The tetraploid and the triploids produced no seeds and relied on rhizomes for propagation. Chromosome sizes of all species were small, ranging from 0.5 to 2.1 μm, which prevented karyotype analysis. The fact that nine of 11 species studied were triploid indicates that triploidy may have some type of competitive advantage over the diploid and tetraploid. In addition, the triploids are popular commercially because of abundant rhizome production and this may contribute to their wide distributions.

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The irritant effect of Dieffenbachia sap is attributed to protelytic enxymes but calcium oxalate crystals are considered to puncture cells and allow enzyme entrance. To date, no detailed study of the location, type, or frequency of calcium oxalate crystals in Dieffenbachia species or cultivars has been undertaken. To do so, three uniform tissue culture plantlets of Dieffenbachia `Carina',`Rebecca' or `Star Bright' were transpanted into 15 cm pots, grown in a shaded greenhouse under 385 μmol·m-2·s-1 and fertigated with 20 N-8.7 P-16.6 K water-soluble fertilizer at N concentrations of 200 mg·L-1 twice weekly. Ten weeks later, samples of stem, root, and leaves were taken from 4 pots of each cultivar to determine the distribution and type of calcuium oxalate crystals in each plant organ via polarized light microscopy. Two types of calcium oxlate crystals, raphides and druses, were found in the stem, leaves and roots. Druse density increased as leaves andd stems matured while the number of raphide idioblasts remained relatively constant. Crystal density was highest at lateral initation sites of buds and roots. Significant differences were found in crystal density among cultivars even though `Carina' and `Star Bright' are sports selected from `Camille'. This suggests that reduction of calcium oxalate density of Dieffenbachia cultivars is possible through breeding.

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Calathea, the largest genus in the family Marantaceae, is composed of 100 species native to tropical America in moist or swampy forest habitats. Because of their brilliant patterns of leaf color and different textures plus ability to tolerate low light levels, calatheas have been widely produced as ornamental foliage plants for interiorscaping. Thus far, genetic relationships among its species and cultivars have not been documented. This study analyzed the relationships of 34 cultivars across 14 species using amplified fragment length polymorphism (AFLP) markers. Six EcoR I + 2/Mse I + 3 primer set combinations were used in this investigation. Each selected primer set generated 105 to 136 scorable fragments. A total of 733 AFLP fragments were detected of which 497 were polymorphic (68%). A dendrogram was constructed using the unweighted pair-group method of arithmetic averages (UP-GMA) technique and a principal coordinated analysis (PCOA) was used to analyze the relationships. The 34 cultivars were divided into four clusters. Cluster I had 19 cultivars derived from C. roseo-picta and C. loesnerii with Jaccard's similarity coefficients from 0.74 to 0.97, of which six are somaclonal variants or sports and two cultivars are genetic identical. Only C. kennedeae `Helen' is positioned in cluster II. Cluster III had 10 cultivars across seven species; Jaccard's similarity coefficients among them varied from 0.41 to 0.63. Four species were situated in cluster IV with Jaccard's similarity between 0.27 to 0.41. Results from this study indicate that broadening of genetic diversity is needed for cultivars in cluster I as they are the most commonly grown calatheas but genetically are very close.

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Gynura aurantiaca is a colorful foliage plant with creeping stems and velvety purple hairs that cover the green leaves. It grows rapidly, but is cultivated primarily for those attractive purple leaves. Annually during the spring, this plant produces prominent flowers both in appearance and smell, gaudy and malodorous. Flowering coupled with acquiring an over-grown leggy appearance have been key limitations in its production and use in interiorscaping. This study was undertaken to determine if an available commercial plant growth regulator could inhibit flowering. A-Rest (ancymidol), B-Nine (daminozide), Bonzi (paclobutrazol), cycocel (chlormequat chloride) and florel (ethephon) each diluted to three different concentrations were sprayed in two applications in early spring at 2-week intervals. Flowering and bud numbers and plant growth (number of lateral shoots, vine lengths and internode lengths) were recorded. Results indicated that applications of A-Rest, B-Nine, Bonzi and Cycocel, regardless of treatment concentrations, were ineffective in suppressing the flowering of this plant; whereas, florel completely suppressed flowering at the three concentrations used. The florel-treated plants also grew more lateral shoots, which produced a compact and dense bush-look, indicating that appropriate concentrations of florel application not only will stop flowering of purple passion but can also improve and prolong its aesthetic value as a potted or hanging-basket interior plant.

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Silicon (Si) is the second most-abundant element in soils, and its concentration in soil solution ranges from 0.1 to 0.6 mm, which is the same concentration range as some of the major nutrient elements such as calcium, magnesium, phosphorus, and sulfur. Increasing evidence has recently suggested that Si plays important roles in improving plant growth. However, little information is available on Si effects on container-grown ornamental plants, particularly since most are grown in soilless media where Si sources are greatly limited. The objectives of this research were to evaluate Si absorption and translocation in diverse container-grown ornamental plants and to determine whether Si absorption could improve plant growth. Liners from 39 plant species were potted in peat and pine bark-based soilless media and grown in a shaded greenhouse. Plants were fertigated with a Peter's 24–8–16 water-soluble fertilizer containing 0, 50, and 100 mg·L–1 of Si. Once marketable sizes were reached, plants were harvested and fresh and dry weights determined; Si and other nutrient elements in roots and shoots were measured. Results indicated that 32 of the 39 evaluated species were able to absorb Si, with large quantities further transported to shoots. Of the 32 Si-responsive species, 17 showed significant dry weight increases, whereas the other 15 only exhibited Si absorption and translocation with no apparent growth responses. The seven non-responsive plant species showed no significant increases in neither Si absorption and translocation, nor dry weight.

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Plant tissue culture can induce a variety of genetic and epigenetic changes in regenerated plantlets, a phenomenon known as somaclonal variation. Such variation has been widely used in the ornamental foliage plant industry as a source for selection of new cultivars. In ornamental aroids alone, at least 63 somaclonal-derived cultivars have been released. In addition to morphological differences, many somaclonal aroid cultivars can be distinguished by amplified fragment length polymorphism (AFLP) analysis. However, a few cultivars have no detectable polymorphisms with their parents or close relatives by AFLP fingerprints. It is postulated that DNA methylation may be involved in the morphological changes of these cultivars. In this study, methylation-sensitive amplification polymorphism (MSAP) technique was used to study DNA methylation in selected somaclonal cultivars of Alocasia, Aglaonema, Anthurium, Dieffenbachia, Philodendron, and Syngonium. Results showed that polymorphisms were detected in the somaclonal cultivars, suggesting that DNA methylation polymorphisms may associate with tissue culture-induced mutation in ornamental aroids. This is the first study of methylation variation in somaclonal variants of ornamental foliage plants. The results clearly demonstrate that the MSAP technique is highly efficient in detecting DNA methylation events in somaclonal-derived cultivars.

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Codiaeum variegatum (L.) Blume, commonly known as crotons, are among the most popular ornamental foliage plants cultivated for either landscaping or interiorscaping. Currently, more than 300 cultivars are available; each has a distinct phenotype, particularly in leaf morphology. Thus far, there is no information regarding their genetic relationships. In this study, genetic relatedness of 44 cultivars of C. variegatum was investigated using amplified fragment length polymorphism (AFLP) markers. Fourteen primer combinations generated a total of 549 AFLP fragments, which were used to estimate genetic distances and construct dendrograms based on the neighbor-joining method. The 44 cultivars were divided into seven clusters, which concurred with the known history of croton geographical isolation, adaptation, introduction, and breeding activities but differed from the classification made by the Croton Society based on leaf morphology. The established genetic relationships could be important for future germplasm identification and conservation and new cultivar development. Additionally, genetic distance among the 44 cultivars was 0.322 or less, indicating that they have a narrow genetic base. The narrow genetic base may indicate that the cultivars were derived from a common progenitor. On the other hand, 81% of the 549 fragments were polymorphic and the average polymorphic information content was 0.22, which suggests that the cultivars are genetically highly polymorphic. The high polymorphisms may be attributed to significant gene loss or gain facilitated by mutation and/or chromosome variation, thus contributing to a wide range of leaf morphological differences among cultivars.

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Syngonium podophyllum ‘White Butterfly’, one of the most popular ornamental foliage plants, is propagated almost exclusively through in vitro shoot culture. Ex vitro rooting, however, has been associated with severe Myrothecium leaf spot (Myrothecium roridum Tode ex Fr.). The objective of this study was to establish a method for regenerating well-rooted plantlets before ex vitro transplanting. Leaf and petiole explants were cultured on a Murashige and Skoog (MS) basal medium supplemented with N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU), N-phenyl-N′-1,2,3-thiadiazol-5-ylurea (TDZ), 6-benzyladenine (BA), or N-isopentenylaminopurine (2iP) with α-naphthalene acetic acid (NAA) and 2,4-dichlorophenoxyacetic acid (2,4-D), respectively. Calli formed from leaf explants cultured on the basal medium supplemented with CPPU or TDZ with 2,4-D or with NAA as well as from petiole explants cultured on the medium supplemented with BA, CPPU, or TDZ with 2,4-D or NAA. The calli, however, failed to differentiate, and shoot organogenesis did not occur. Culture of nodal explants on the MS basal medium supplemented with 9.84 μm 2iP, 8.88 μm BA, 8.07 μm CPPU, or 9.08 μm TDZ with 2.26 μm 2,4-D resulted in the formation of protocorm-like bodies, adventitious shoots, and subsequently well-rooted plantlets. MS basal medium supplemented with 19.68 μm 2iP and 1.07 μm NAA resulted in the highest percentage (92.9%) of nodal explants producing protocorm-like bodies and an average of 16.9 well-rooted plantlets per nodal explant. Adventitious shoots were able to root in the initial induction medium, but better root development occurred after shoots with protocorm-like bodies were transferred onto MS basal medium supplemented with 9.84 μm 2iP and 2.69 μm NAA. Regenerated plantlets were stable and grew vigorously with 100% survival rates after ex vitro transplanting to a container substrate in a shaded greenhouse.

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Codiaeum variegatum (L.) Blume is one of the most popular ornamental foliage plants. It encompasses more than 300 recognized cultivars valued by their wide range of leaf shapes and vivid foliage colors. Thus far, only limited information is available regarding the genetic basis of their leaf morphological variation. This study investigated the chromosome numbers and karyotypes of seven phenotypically diverse cultivars. Root-tip cells were fixed, mounted, and observed under light microscopy. Results showed that chromosome numbers in the mitotic metaphase of the seven cultivars were high and variable and ranged from 2n = 66, 70, 72, 76, 80, 82, 84, to 2n = 96, indicating that the cultivars are polyploid and some could be aneuploid. Genetic mosaics occurred in one of the seven cultivars. Additionally, each cultivar had its own karyotype. There were no relationships between chromosome numbers or karyotypes and leaf morphology. Results from this study suggest that the morphological diversity among cultivars of this species could be in part attributed to high variation in chromosome numbers and karyotypes.

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