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- Author or Editor: Ryan Contreras x
Platycladus orientalis (L.) Franco (syn. Thuja orientalis L.), Thuja occidentalis L., and T. plicata D. Don. are conifers often used in the landscape. Most of the available cultivars of these species share the character of having foliage that turns an off-color during winter as a result of photoinhibition. Tetraploids of the related japanese-cedar [Cryptomeria japonica (L. f.) D. Don.] have exhibited greener color retention than diploids during winter and a recent report described a simple technique to double its chromosomes. The technique used to double the chromosome number of C. japonica was applied to the three species mentioned to determine if it would be effective for inducing polyploidy and, if so, optimal duration of treatment. Seedlings were treated at the cotyledon stage for 0 (control), 10, 20, or 30 days with an aqueous solution containing 150 μM oryzalin + 0.1% Tween® 20 using a standard household spray bottle that created a fine mist. No tetraploids were observed for any species in control treatments, indicating all recovered tetraploids resulted from applying oryzalin. Tetraploids were observed for all other treatments except T. plicata at 30 days. Efficacy ranged from 0% to 27.1% of transplanted seedlings being tetraploid. There was a quadratic relationship between duration of treatment and percent tetraploids in T. occidentalis and T. plicata and a linear relationship for P. orientalis. Based on regression analysis, the optimal duration of treatment was 20.5 days for T. occidentalis and 13.9 days for T. plicata. The highest percent tetraploids recovered for P. orientalis was at 30 days and it is unclear if increasing duration beyond this would continue increasing percent tetraploids recovered. Morphology was not useful in early identification of tetraploids for any species.
Wide hybridization can potentially lead to the combination of diverse traits, but these hybrids are often sterile as is the case with the inter-subgeneric hybrid Rhododendron `Fragrant Affinity'. Induction of polyploidy can restore chromosome homology and fertility in wide hybrids. In this study we successfully developed an allopolyploid form of R. `Fragrant Affinity' using oryzalin as a mitotic inhibitor and chromosome doubling agent. Approximate genome size (2C), determined using flow cytometry, was 1.6 pg for the diploid and 3.2 pg for the allotetraploid. Pollen viability, determined by staining and germination tests, was 4% and 0%, respectively for the diploid and 68% and 45%, respectively for the allotetraploid. No seeds were produced when the diploid R. `Fragrant Affinity' was crossed with pollen from viable diploid and tetraploid parents. The allotetraploid produced viable seeds and seedlings when crossed with viable pollen from either diploid or tetraploid parents, including self pollination, demonstrating restored fertility. Additional crosses were successfully completed using the allotetraploid as part of an ongoing breeding program to develop new fragrant, cold hardy, evergreen rhododendron.
Althea (Hibiscus syriacus) is an ornamental shrub prized for its winterhardiness, flower colors, and unique flower forms, including single-flowered and double-flowered types. Although floral traits are most important for breeders of althea, little is known about their segregation patterns. The objective of this study was to determine segregation patterns in flower color, including eyespot, among hybrid seedlings of elite taxa. Over 4 years, more than 3100 flowering seedlings were produced for observation of F1, F2, and backcross families. For each plant, data were collected including presence of eyespot and petal body color (CIEL*a*b*) using a colorimeter. Recessive testcrosses and χ2 analyses were performed among three taxa (‘Buddha Belly’, ‘Diana’, and White Chiffon®), and between this recessive group and a suite of colorful taxa. Self-pollination and intercrosses within homozygous dominant and homozygous recessive groups further confirmed their genotypes. Based on these results, we propose that eyespot is controlled by a single gene called spotless, named for the recessive allele that results in a complete elimination of color in flowers. Crosses that resulted in seedlings that all produced eyespots were observed to segregate for color in the petal body. Of these, one group produced white to blush pink petals, which was recessive to full color. Recessive testcrosses and χ2 analyses were performed among nine taxa exhibiting eyespots with white to blush petal bodies, and between taxa with full-color petal bodies. These testcrosses resulted in a putative homozygous dominant group composed mostly of blue and dark pink taxa, whereas the heterozygous group was composed mostly of pink taxa. Spotless taxa were also added to these two groups, suggesting an epistatic interaction with the spotless allele. Based on these results, we propose that petal body color is controlled by a single gene called geisha, named for the recessive allele that produces white to blush-pink petal bodies and dark red eyespot. This trait exhibits incomplete dominance and is under epistatic control by spotless. Geisha-type flowers lack pigment in the petal body, or exhibit a blush pink, likely produced by low levels of cyanidin, peonidin, and pelargonidin. The interaction and segregation of these two genes was confirmed in F1, F2, and backcross families from two crosses: Lil’ Kim™ × Blue Chiffon™ and Fiji™ × White Chiffon®. This study on segregation of flower color in H. syriacus contributes substantial and useful information on inheritance of color and will facilitate targeted breeding to improve this vibrant ornamental shrub.
Acer is a large and important genus of woody plants most commonly encountered as small to large trees in urban landscapes. Considerable investigation has been devoted to addressing the taxonomy of maples, but little is known about genome sizes across the genus. Relatively more work has been conducted to determine chromosome numbers and ploidy of more species, but much could be gained by expanding knowledge of genome sizes in combination with traditional cytology. Furthermore, base pair (bp) composition may have implications for a species’ adaptability and also impacts nucleic acid stability at high temperatures. Our objectives were to determine the genome size of 195 accessions of maples, assign ploidy to each using inference as well as cytology, and determine base composition of a subset of 48 accessions. Most species had small genome sizes (1.4–3.5 pg) with the exception of section Rubra, which contains many polyploids. Holoploid genome sizes ranged from 1.39 to 6.10 pg, with the latter being interpreted as 9x. The mean monoploid genome sizes (1Cx) ranged from 0.43 pg in A. carpinifolium (section Indivisa) to 1.66 pg in A. caudatifolium (section Macrantha); mean monoploid genome sizes were significantly different among sections. Forty-four of the 48 accessions measured using both fluorochromes had greater estimates with 4′,6-diamidino-2-phenylindole (DAPI) than propidium iodide (PI). The proportion of the genome composed of guanosine and cytosine (GC%) among the taxa evaluated in this study ranged from just 38.61% to 43.96% and did not appear to be related to ecological adaptability or urban tolerance among these taxa.
Prunus laurocersaus L. (2n = 22x = 176), common cherrylaurel, is an evergreen shrub generally used as a hedge or screen. This species produces large drupes that are a nuisance when they drop on walkways or deposited by birds and also has escaped cultivation in parts of northwestern United States, which has raised concern about the invasive potential of common cherrylaurel. Therefore, a fruitless and sterile form of common cherrylaurel is desirable. As part of our efforts to develop sterile common cherrylaurel cultivars, we conducted two experiments to induce chromosome doubling using in vitro exposure of ‘Otto Luyken’ and ‘Schipkaensis’ cherrylaurel to oryzalin. For ‘Otto Luyken’ (Expt. 1), we tested the effects of treatment duration (1, 2, 14, or 28 days) and oryzalin concentration (0, 6.25, 12.5, 25, 50, 100, or 150 μm) applied in a liquid phase over explants. In Expt. 2, we treated ‘Schipkaensis’ cherrylaurel shoots with a single duration of 28 days and exposed explants to the same varying concentrations of oryzalin incorporated into the solidified medium. In Expt. 1, the 14-day treatment had reduced survival compared with 1- and 2-day treatments and there was still greater mortality in the 28-day treatment. Duration of the treatment affected mortality more than oryzalin concentration. Sixteen treatment combinations resulted in 44x plants. The percentage of 44x plants increased with concentration in the 1- and 2-day treatments up to 30% of treated shoots at 150 μm. Overall, the longer duration treatments in Expt. 1 were less efficient for inducing 44x plants. Expt. 2 was less effective for inducing homogenous 44x plants. It is unclear if this is due to treatment or cultivar differences but the highest concentration was 8% in the 6.25 μm treatment.
Lilacs (Syringa sp.) are a group of ornamental trees and shrubs in the Oleaceae composed of 22–30 species from two centers of diversity: the highlands of East Asia and the Balkan-Carpathian region of Europe. There are six series within the genus Syringa: Pubescentes, Villosae, Ligustrae, Ligustrina, Pinnatifoliae, and Syringa. Intraspecific and interspecific hybridization are proven methods for cultivar development. However, reports of interseries hybridization are rare and limited to crosses among taxa in series Syringa and Pinnatifoliae. Although hundreds of lilac cultivars have been introduced, fertility and cross-compatibility have yet to be formally investigated. Over 3 years, a cross-compatibility study was performed using cultivars and species of shrub-form lilacs in series Syringa, Pubescentes, and Villosae. A total of 114 combinations were performed at an average of 243 ± 27 flowers pollinated per combination. For each combination, we recorded the number of inflorescences and flowers pollinated as well as number of capsules, seed, seedlings germinated, and albino seedlings. Fruit and seed were produced from interseries crosses, but no seedlings were recovered. A total of 2177 viable seedlings were recovered from interspecific and intraspecific combinations in series Syringa, Pubescentes, and Villosae. Albino progeny were produced only from crosses with Syringa pubescens ssp. patula ‘Miss Kim’. In vitro germination was attempted on 161 seed from interseries crosses, resulting in three germinations from S. pubescens Bloomerang® x Syringa vulgaris ‘Ludwig Spaeth’. None survived, yet cotyledons produced callus for future efforts to induce embryogenic shoots. This study is a comprehensive investigation of lilac hybridization, and the knowledge gained will aid future efforts in lilac cultivar development.