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The genus Cotoneaster is composed of ≈400 species with a wide variety of growth habits and forms. These hardy landscape shrubs used to be commonplace because of their low maintenance and landscape functionality. However, the interest in and sales of cotoneaster have decreased for a variety of reasons, with the greatest being its susceptibility to a bacterial disease fire blight caused by Erwinia amylovora. The resistances of 15 different genotypes of Cotoneaster to a wild-type strain of Erwinia amylovora (Ea153) and a strain LA635 that has a natural mutation in avrRpt2 that encodes for a type III secretion effector were tested separately by inoculating leaves. Fire blight resistance was assessed by calculating the percent shoot necrosis (PSN) [PSN = 100 × (lesion length ÷ total branch length)] at 6 to 8 weeks after inoculation. Across all experiments, Cotoneaster genotypes H2011-01-002 and C. ×suecicus ‘Emerald Sprite’ consistently had the lowest PSN values when inoculated with either strain. Cotoneaster ×suecicus ‘Emerald Beauty’ was significantly more resistant to Ea153 than to LA635, whereas C. splendens was significantly more susceptible to Ea153 than to LA635.
Kristin E. Neill; Ryan N. Contreras; Virginia O. Stockwell; Hsuan Chen. Screening Cotoneaster sp. for Resistance to Fire Blight Using Foliar Inoculation with Two Strains of Erwinia amylovora. HortScience 2021, 56, 1 -7.
AMA StyleKristin E. Neill, Ryan N. Contreras, Virginia O. Stockwell, Hsuan Chen. Screening Cotoneaster sp. for Resistance to Fire Blight Using Foliar Inoculation with Two Strains of Erwinia amylovora. HortScience. 2021; 56 (7):1-7.
Chicago/Turabian StyleKristin E. Neill; Ryan N. Contreras; Virginia O. Stockwell; Hsuan Chen. 2021. "Screening Cotoneaster sp. for Resistance to Fire Blight Using Foliar Inoculation with Two Strains of Erwinia amylovora." HortScience 56, no. 7: 1-7.
Common lilac is an important flowering shrub that accounts for ≈$20 million of sales in the U.S. nursery industry. Cultivar improvement in common lilac has been ongoing for centuries, yet little research has focused on shortening the multiple-year juvenility period for lilacs and the subsequent time required between breeding cycles. The practice of direct-sowing of immature “green” seed has been shown to reduce juvenility in some woody plants, but it has not been reported for common lilac. This study investigated the effects of seed maturity [weeks after pollination (WAP)], pregermination seed treatment (direct-sown vs. cold-stratified), and postgermination seedling chilling on the germination percentage, subsequent plant growth, and time to flower on lilac seedlings. All seedlings were derived from the female parent ‘Ludwig Spaeth’ and the male parent ‘Angel White’. Seeds harvested at 15 and 20 WAP resulted in 58% (sd ± 9.9%) and 80% (sd ± 9.0%) germination, respectively, which were similar to that of dry seed collected at 20 WAP with stratification (62% ± 4.2%). Seedlings from the green seed collected at 15 and 20 WAP were also approximately three-times taller than those of dry seed groups DS1, DS2, and DS3 after the first growing season. Over the next two growing seasons, there were no differences in seedling height across all treatments. Flowering occurred at the beginning of the fourth season and without differences among treatments. These results indicate that the collection and direct sowing of immature, green seed can be used to successfully grow lilac seedlings, but that they do not reduce the juvenility period. However, this method can provide more vegetative growth in year one to observe early vegetative traits such as leaf color, and it can provide more material for DNA extraction to support molecular research.
Tyler C. Hoskins; Jason D. Lattier; Ryan N. Contreras. Sowing Green Seed Without Stratification Does Not Shorten Juvenility or Increase Plant Size in Common Lilac (Syringa vulgaris). HortScience 2020, 55, 1 -7.
AMA StyleTyler C. Hoskins, Jason D. Lattier, Ryan N. Contreras. Sowing Green Seed Without Stratification Does Not Shorten Juvenility or Increase Plant Size in Common Lilac (Syringa vulgaris). HortScience. 2020; 55 (11):1-7.
Chicago/Turabian StyleTyler C. Hoskins; Jason D. Lattier; Ryan N. Contreras. 2020. "Sowing Green Seed Without Stratification Does Not Shorten Juvenility or Increase Plant Size in Common Lilac (Syringa vulgaris)." HortScience 55, no. 11: 1-7.
Maples are common street and shade trees throughout the temperate zone. They are widely used for their wide range of ornamental traits and adaptability, particularly to urban settings. Unfortunately, some species such as Acer tataricum ssp. ginnala (Amur maple) and A. platanoides (Norway maple) have escaped cultivation to become pests or in some cases threaten native flora. However, these species remain economically important and are still asked for by name. To ameliorate potential future ecological damage from additional escapes, we have been breeding for sterile forms using ploidy manipulation and backcrossing to develop triploids. We began with a series of experiments to develop tetraploids of Amur, Norway, and trident (A. buergerianum) maples. Treatment of seedlings at the cotyledon or first true leaf stage was successful in inducing tetraploids of each species. Mortality, cytochimeras, and tetraploids varied among species. After identifying tetraploids, they were field planted alongside diploid cultivars and seedlings, which served as pollinizers in open-pollination. Seedlings derived from open-pollinated tetraploids were generally found to be a high percentage triploids. Thus far, no Norway or trident maple triploids have flowered but after three years we observed five, 22, and 22 Amur maple triploids flowering over three respective years with no seedlings recovered to date. Further evaluation is required but our findings are encouraging that the triploids we have developed thus far will be sterile and provide new cultivars for nursery growers and land managers.
Ryan Contreras; Tyler Hoskins. Developing Triploid Maples. Horticulturae 2020, 6, 70 .
AMA StyleRyan Contreras, Tyler Hoskins. Developing Triploid Maples. Horticulturae. 2020; 6 (4):70.
Chicago/Turabian StyleRyan Contreras; Tyler Hoskins. 2020. "Developing Triploid Maples." Horticulturae 6, no. 4: 70.
Cape hyacinth (Galtonia candicans) is a geophytic herbaceous perennial from South Africa. It produces large inflorescences of pendulous white flowers during mid to late summer, followed by capsules filled with copious amounts of seed. The species has potential as a low-water-use landscape plant, but lodging and excessive seed production, which pose a risk of escape or invasion, are issues that should be addressed before marketing. Ethyl methanesulfonate (EMS) is a chemical mutagen known to induce usable mutations including dwarfing and sterility. We exposed seeds of cape hyacinth to increasing concentrations of EMS (0%, 0.2%, 0.4%, 0.6%, 0.8%, and 1%). Increased concentrations of EMS resulted in a linear decrease in seed germination when not exposed to a presoak treatment in water before exposure to EMS. No seedlings survived or were viable to field plant at 0.6%, 0.8%, or 1%. Resulting plants were field planted in 2013 and evaluated during 2014 and 2015. In both years, the inflorescence height at first flower, average seed number per capsule, and percent lodging were reduced in EMS-treated plants compared with controls. In 2015, pollen staining was evaluated and was reduced from 83% in control to less than 3% in the 0.4% treatment. Our study demonstrated that EMS is a viable option to reduce height and decrease seed set in cape hyacinth.
Ryan N. Contreras; Kim Shearer. Exposing Seeds of Galtonia candicans to Ethyl Methanesulfonate Reduced Inflorescence Height, Lodging, and Fertility. HortScience 2020, 55, 621 -624.
AMA StyleRyan N. Contreras, Kim Shearer. Exposing Seeds of Galtonia candicans to Ethyl Methanesulfonate Reduced Inflorescence Height, Lodging, and Fertility. HortScience. 2020; 55 (5):621-624.
Chicago/Turabian StyleRyan N. Contreras; Kim Shearer. 2020. "Exposing Seeds of Galtonia candicans to Ethyl Methanesulfonate Reduced Inflorescence Height, Lodging, and Fertility." HortScience 55, no. 5: 621-624.
Lilacs (Syringa sp.) have been used as ornamental plants since the mid-16th century and remain important in modern gardens due to their attractive and fragrant flowers. However, a short flowering season is a critical drawback for their ornamental value. Breeders have identified remontancy (reblooming) in dwarf lilac (Syringa pubescens), and have tried to introgress this trait into related species by interspecific hybridization. Molecular tools for lilac breeding are limited because of the shortage of genome sequence knowledge and currently no molecular markers are available to use in breeding for remontancy. In this study, an F1 population from crossing Syringa meyeri ‘Palibin’ × S. pubescens ‘Penda’ Bloomerang® Purple was created and subjected to genotyping-by-sequencing (GBS) analysis and phenotyped for remontancy. Plants were categorized as remontant, semi-remontant, and nonremontant based on the relative quantity of inflorescences during the second flush of flowers. A total of 20,730 single-nucleotide polymorphism (SNP) markers from GBS were used in marker-trait association to find remontant-specific marker(s) without marker position information. Two SNP markers, TP70580 (A locus) and TP82604 (B locus), were correlated with remontancy. The two loci showed a partial epistasis and additive interaction effects on the level of remontancy. Accumulation of recessive alleles at the two loci was positively correlated with increased reblooming. For example, 87% of aabb plants were remontant, and only 9% were nonremontant. In contrast, 100% of AaBB plants were nonremontant. These two SNP markers associated with remontancy will be useful in developing markers for future breeding and demonstrate the feasibility of developing markers for breeding woody ornamental taxa that lack a reference genome or extensive DNA sequence information.
Hsuan Chen; Jason D. Lattier; Kelly Vining; Ryan N. Contreras. Two SNP Markers Identified Using Genotyping-by-Sequencing Are Associated with Remontancy in a Segregating F1 Population of Syringa meyeri ‘Palibin’ × S. pubescens ‘Penda’ Bloomerang®. Journal of the American Society for Horticultural Science 2020, 145, 104 -109.
AMA StyleHsuan Chen, Jason D. Lattier, Kelly Vining, Ryan N. Contreras. Two SNP Markers Identified Using Genotyping-by-Sequencing Are Associated with Remontancy in a Segregating F1 Population of Syringa meyeri ‘Palibin’ × S. pubescens ‘Penda’ Bloomerang®. Journal of the American Society for Horticultural Science. 2020; 145 (2):104-109.
Chicago/Turabian StyleHsuan Chen; Jason D. Lattier; Kelly Vining; Ryan N. Contreras. 2020. "Two SNP Markers Identified Using Genotyping-by-Sequencing Are Associated with Remontancy in a Segregating F1 Population of Syringa meyeri ‘Palibin’ × S. pubescens ‘Penda’ Bloomerang®." Journal of the American Society for Horticultural Science 145, no. 2: 104-109.
Sweetbox (Sarcococca confusa) is an evergreen shrub valued for attractive foliage, winter fragrance, black fruit, as well as shade and drought tolerance. The high degree of apomixis in Sarcococca limits the effectiveness of conventional breeding practices. However, mutation breeding may be a valuable tool to induce variation in seedling crops. As such, a study was conducted to expose seeds of S. confusa to ethyl methanesulfonate (EMS) at varying concentrations and exposure durations, and to evaluate the effects on seed germination, growth, and relative frequency of polyembryony. In 2010, seeds of S. confusa were treated with 0%, 0.2%, 0.4%, 0.8%, and 1.2% EMS for 24 and 48 hours. Seeds were sown and the relative germination and occurrence of polyembryony were recorded. Seedlings were later evaluated for size and phenotypic variation in the subsequent growing seasons. Percent germination was found to decrease with increasing EMS rates in the 24- and 48-hour treatments. The occurrence of polyembryony also decreased with increasing EMS rates in the 24-hour treatment but was observed to be greatest at 0.2% EMS. No significant differences in plant size index (SI) were found after four growing seasons. When mature, seeds were collected from any plants that bore fruit in each treatment and were then sown. The percentage of plants that bore fruit in each treatment decreased with increasing EMS rates, although the germination rate of these seeds did not differ. A chlorophyll mutant and several dwarf forms were identified in this population as well. They have been propagated asexually for future evaluation as new cultivars. This study demonstrates the utility of chemical mutagenesis to induce phenotypic variation in S. confusa while reducing the rate of polyembryony.
Tyler Hoskins; Ryan N. Contreras. Exposing Seeds of Sarcococca confusa to Increased Concentrations and Durations of Ethyl Methanesulfonate Reduced Seed Germination, Twinning, and Plant Size. HortScience 2019, 54, 1902 -1906.
AMA StyleTyler Hoskins, Ryan N. Contreras. Exposing Seeds of Sarcococca confusa to Increased Concentrations and Durations of Ethyl Methanesulfonate Reduced Seed Germination, Twinning, and Plant Size. HortScience. 2019; 54 (11):1902-1906.
Chicago/Turabian StyleTyler Hoskins; Ryan N. Contreras. 2019. "Exposing Seeds of Sarcococca confusa to Increased Concentrations and Durations of Ethyl Methanesulfonate Reduced Seed Germination, Twinning, and Plant Size." HortScience 54, no. 11: 1902-1906.
Hibiscus syriacus is a woody shrub in the Malvaceae family that is common in landscapes due to its broad adaptability and variable ornamental characteristics. Interspecific hybridization has been used to improve Hibiscus by building novel floral traits, hybrid vigor, and hybrid infertility. A few interspecific hybrid Hibiscus cultivars (H. syriacus × H. paramutabilis), such as Lohengrin and Resi, are notable because of their vigorous vegetative growth, female infertility, and large flowers. However, little is known about the male fertility and breeding potential of these hybrid cultivars, which could increase flower size by backcrossing to H. syriacus. In this study, we estimated male fertility of the two hybrid cultivars by acetocarmine staining and in vivo pollination and assessed selection methods for floral traits, specifically flower size and petal number. A BC1F1 population of 294 individuals was developed by crossing hybrid cultivars Lohengrin or Resi with a variety of double-flowered H. syriacus cultivars. A negative correlation between petal number and petal area was detected by quantile regression, which is a method that circumvents the problem of simple linear regression, which violates statistical assumptions. Quantile regression was used to build simultaneous selection thresholds for different levels of required stringency. As expected, the female fertility of hybrid cultivars was extremely low or zero; however, the male fertility of hybrid cultivars was not reduced compared with H. syriacus cultivars. A negative linear correlation between the petal number and petal area of the BC1F1 individuals was observed. In addition, quantile regression was recommended to set a single selection threshold to be applied to the selection of two negatively correlated traits, which was more effective than independent selection of petal numbers and petal areas among progeny.
Hsuan Chen; Lan Xue; Tong Li; Ryan N. Contreras. Quantile Regression Facilitates Simultaneous Selection of Negatively Correlated Floral Traits among BC1F1 Progeny of Male-fertile Hybrid Hibiscus Cultivars Lohengrin and Resi (H. syriacus × H. paramutabilis). Journal of the American Society for Horticultural Science 2019, 144, 70 -76.
AMA StyleHsuan Chen, Lan Xue, Tong Li, Ryan N. Contreras. Quantile Regression Facilitates Simultaneous Selection of Negatively Correlated Floral Traits among BC1F1 Progeny of Male-fertile Hybrid Hibiscus Cultivars Lohengrin and Resi (H. syriacus × H. paramutabilis). Journal of the American Society for Horticultural Science. 2019; 144 (1):70-76.
Chicago/Turabian StyleHsuan Chen; Lan Xue; Tong Li; Ryan N. Contreras. 2019. "Quantile Regression Facilitates Simultaneous Selection of Negatively Correlated Floral Traits among BC1F1 Progeny of Male-fertile Hybrid Hibiscus Cultivars Lohengrin and Resi (H. syriacus × H. paramutabilis)." Journal of the American Society for Horticultural Science 144, no. 1: 70-76.
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.
Ryan N. Contreras; Kimberly Shearer. Genome Size, Ploidy, and Base Composition of Wild and Cultivated Acer. Journal of the American Society for Horticultural Science 2018, 143, 470 -485.
AMA StyleRyan N. Contreras, Kimberly Shearer. Genome Size, Ploidy, and Base Composition of Wild and Cultivated Acer. Journal of the American Society for Horticultural Science. 2018; 143 (6):470-485.
Chicago/Turabian StyleRyan N. Contreras; Kimberly Shearer. 2018. "Genome Size, Ploidy, and Base Composition of Wild and Cultivated Acer." Journal of the American Society for Horticultural Science 143, no. 6: 470-485.
Genome size variation can be used to investigate biodiversity, genome evolution, and taxonomic relationships among related taxa. Plant breeders use genome size variation to identify parents useful for breeding sterile or improved ornamentals. Lilacs (Syringa) are deciduous trees and shrubs valued for their fragrant spring and summer flowers. The genus is divided into six series: Syringa (Vulgares), Pinnatifoliae, Ligustrae, Ligustrina, Pubescentes, and Villosae. Reports conflict on genome evolution, base chromosome number, and polyploidy in lilac. The purpose of this study was to investigate genome size and ploidy variation across a diverse collection. Flow cytometry was used to estimate monoploid (1Cx) and holoploid (2C) genome sizes in series, species, cultivars, and seedlings from parents with three ploidy combinations: 2x x 2x, 2x x 3x, and 3x x 2x. Pollen diameter was measured to investigate the frequency of unreduced gametes in diploid and triploid Syringa vulgaris cultivars. Three triploids of S. vulgaris were observed: ‘Aucubaefolia’, ‘Agincourt Beauty’, and ‘President Grévy’. Across taxa, significant variations in 1Cx genome size were discovered. The smallest and largest values were found in the interspecific hybrids S. ×laciniata (1.32 ± 0.04 pg) and S. ×hyacinthiflora ‘Old Glory’ (1.78 ± 0.05), both of which are in series Syringa. Series Syringa (1.68 ± 0.02 pg) had a significantly larger 1Cx genome size than the other series. No significant differences were found within series Pubescentes (1.47 ± 0.01 pg), Villosae (1.55 ± 0.02 pg), Ligustrina (1.49 ± 0.05 pg), and Pinnatifoliae (1.52 ± 0.02 pg). For S. vulgaris crosses, no significant variation in 2C genome size was discovered in 2x x 2x crosses. Interploid crosses between ‘Blue Skies’ (2x) and ‘President Grévy’ (3x) produced an aneuploid population with variable 2C genome sizes ranging from 3.41 ± 0.03 to 4.35 ± 0.03 pg. Only one viable seedling was recovered from a cross combination between ‘President Grévy’ (3x) and ‘Sensation’ (2x). This seedling had a larger 2C genome size (5.65 ± 0.02 pg) than either parent and the largest 2C genome size currently reported in lilac. ‘Sensation’ produced 8.5% unreduced pollen, which we inferred was responsible for the increased genome size. No unreduced pollen was discovered in the other diploids examined. Increased ploidy may provide a mechanism for recovering progeny from incompatible taxa in lilac breeding.
Jason D. Lattier; Ryan N. Contreras. Ploidy and Genome Size in Lilac Species, Cultivars, and Interploid Hybrids. Journal of the American Society for Horticultural Science 2017, 142, 355 -366.
AMA StyleJason D. Lattier, Ryan N. Contreras. Ploidy and Genome Size in Lilac Species, Cultivars, and Interploid Hybrids. Journal of the American Society for Horticultural Science. 2017; 142 (5):355-366.
Chicago/Turabian StyleJason D. Lattier; Ryan N. Contreras. 2017. "Ploidy and Genome Size in Lilac Species, Cultivars, and Interploid Hybrids." Journal of the American Society for Horticultural Science 142, no. 5: 355-366.
A tissue culture protocol was developed to germinate immature Prunus lusitanica seeds in vitro. The study was conducted by first identifying the best media for germination, followed by investigating effects of seed conditioning. In Expt. I, seeds were collected 12 weeks after pollination (WAP) ± 1 week and placed on media after removing the pericarp. Eight different MS media (Murashige and Skoog, 1962) were tested (M1–M8) containing two concentrations each of 6-benzylaminopurine (BA), gibberellic acid (GA3), and sucrose. The longest shoots resulted from M4 (1.45 µm GA3, 6 µm BA, and 30 g·L−1 sucrose), followed by M1 (0 µm GA3, 3 µm BA, and 30 g·L−1 sucrose). Radicle and shoot emergence was greater than or equal to 90% for M1, M3, and M4 after a stratification treatment. In Expt. II, M1 was used to test root and shoot emergence at 6, 9, and 12 WAP, with and without cold stratification. Little success was seen 6 and 9 WAP, with only callus development in 6 WAP, nonstratified seed. Cold stratification increased shoot emergence in the 12 WAP group from 4% to 28%, appearing to be critical for shoot emergence. If the cotyledons are retained on the seed, future efforts to expedite breeding of P. lusitanica using in vitro germination should not be collected before 12 WAP and will benefit from cold stratification before germinating on M1 or M4. Chemical names: 6-benzylaminopurine (BA), gibberellic acid (GA3).
Justin A. Schulze; Jason D. Lattier; Ryan N. Contreras. In Vitro Germination of Immature Prunus lusitanica Seed. HortScience 2017, 52, 1122 -1124.
AMA StyleJustin A. Schulze, Jason D. Lattier, Ryan N. Contreras. In Vitro Germination of Immature Prunus lusitanica Seed. HortScience. 2017; 52 (8):1122-1124.
Chicago/Turabian StyleJustin A. Schulze; Jason D. Lattier; Ryan N. Contreras. 2017. "In Vitro Germination of Immature Prunus lusitanica Seed." HortScience 52, no. 8: 1122-1124.
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.
Jason D. Lattier; Ryan N. Contreras. Intraspecific, Interspecific, and Interseries Cross-compatibility in Lilac. Journal of the American Society for Horticultural Science 2017, 142, 279 -288.
AMA StyleJason D. Lattier, Ryan N. Contreras. Intraspecific, Interspecific, and Interseries Cross-compatibility in Lilac. Journal of the American Society for Horticultural Science. 2017; 142 (4):279-288.
Chicago/Turabian StyleJason D. Lattier; Ryan N. Contreras. 2017. "Intraspecific, Interspecific, and Interseries Cross-compatibility in Lilac." Journal of the American Society for Horticultural Science 142, no. 4: 279-288.
Chromosome numbers are an important botanical character for multiple fields of plant sciences, from plant breeding and genetics to systematics and taxonomy. Accurate chromosome counts in root tips of woody plants are often limited by their small, friable roots with numerous, small chromosomes. Current hydrolysis and enzyme digestion techniques require handling of roots before the root squash. However, optimum chromosome spread occurs when the cell walls have degraded past the point of easy handling. Here, we present a new enzyme digestion protocol that is fast, efficient, and flexible. This protocol reduces handling of the roots allowing for long-duration enzyme digestion. Digestions are performed on a microscope slide, eliminating the need for handling digested cells with forceps or pipettes. To illustrate the flexibility of this method across woody plant taxa, we performed chromosome counts on five angiosperms and one gymnosperm. Ploidy levels included diploids, triploids, and tetraploids with chromosome numbers ranging from 2n = 16 to 2n = 80. The range of holoploid 2C genome sizes spanned 1.54–24.71 pg. This protocol will provide a useful technique for plant cytologists working with taxa that exhibit a wide range of genome size and ploidy levels.
Jason D. Lattier; Hsuan Chen; Ryan N. Contreras. Improved Method of Enzyme Digestion for Root Tip Cytology. HortScience 2017, 52, 1029 -1032.
AMA StyleJason D. Lattier, Hsuan Chen, Ryan N. Contreras. Improved Method of Enzyme Digestion for Root Tip Cytology. HortScience. 2017; 52 (7):1029-1032.
Chicago/Turabian StyleJason D. Lattier; Hsuan Chen; Ryan N. Contreras. 2017. "Improved Method of Enzyme Digestion for Root Tip Cytology." HortScience 52, no. 7: 1029-1032.
Prunus lusitanica (2n = 8x) and Prunus laurocerasus (2n = 22x) are evergreen woody shrubs commonly used in landscapes across the United States and Europe. To reduce the difference in ploidy between these species and with the expectation of successful hybridization, an experiment was performed to double the chromosome number of P. lusitanica. Colchicine was applied at 0%, 0.2%, 0.4%, and 0.8% (w/v), and 125 µM oryzalin as a viscous liquid to the apical meristem of open-pollinated P. lusitanica seedlings. Solutions were semisolidified using 0.55% agar (w/v). Cellular penetration was increased by adding 1% dimethyl sulfoxide (v/v) in all groups except oryzalin. As a result, three chromosome doubled (2n = 16x) plants, one 2n = 12x plant, and 14 cytochimeras (2n = 8x + 16x) were recovered. Application of 125 µM oryzalin had a meristem-survival rate of 17%, statistically lower than all other treatments. The oryzalin treatment also produced the highest number of altered ploidy seedlings. Oryzalin at 125 µM was the most effective chromosome doubling agent in this experiment. Phenotypic examination indicated that chromosome doubled (2n = 16x) plants displayed shorter stems, thicker leaves, and fewer but larger guard cells than the untreated controls.
Justin A. Schulze; Ryan N. Contreras. In Vivo Chromosome Doubling of Prunus lusitanica and Preliminary Morphological Observations. HortScience 2017, 52, 332 -337.
AMA StyleJustin A. Schulze, Ryan N. Contreras. In Vivo Chromosome Doubling of Prunus lusitanica and Preliminary Morphological Observations. HortScience. 2017; 52 (3):332-337.
Chicago/Turabian StyleJustin A. Schulze; Ryan N. Contreras. 2017. "In Vivo Chromosome Doubling of Prunus lusitanica and Preliminary Morphological Observations." HortScience 52, no. 3: 332-337.
‘Schipkaensis’ common cherrylaurel (Prunus laurocerasus) is an important nursery crop across the United States. In our breeding efforts to reduce shot-hole symptoms and weediness, we have created chromosome doubled forms of this cultivar. Vegetative propagation is an important factor in nursery production, and we have found no studies that have looked at comparative adventitious rooting of stem cuttings using induced polyploids. The objective of this research was to determine if rooting ability varied between these two ploidy levels. Semihardwood stem cuttings from wild-type (22x) and polyploid (44x) ploidy levels were taken at the end of July 2015 and the beginning of July 2016. Cuttings were dipped in 1030 ppm (0.10%) indole-3-butyric acid (IBA) and 660 ppm (0.066%) 1-naphthaleneacetic acid (NAA) before being set in rooting substrate. After 1 month, cuttings were removed from substrate and data collected. Data included; rooting percentage, root number per rooted cutting, average root length, and total root length. In 2015, 88% of the cuttings from the 44x plants and 63% of the cuttings from the 22x plants rooted. In 2016, 100% of cuttings from both ploidy levels rooted. In both years, average root length and total root length were similar between ploidy levels; however, cuttings from 22x plants generally had more roots than those from 44x. Chromosome-doubled ‘Schipkaensis’ common cherrylaurel rooted effectively, and produce transplantable cuttings similar to the standard ploidy.
Justin A. Schulze; Ryan N. Contreras; Carolyn Scagel. Comparing Vegetative Propagation of Two ‘Schipkaensis’ Common Cherrylaurel Ploidy Levels. HortTechnology 2017, 27, 69 -72.
AMA StyleJustin A. Schulze, Ryan N. Contreras, Carolyn Scagel. Comparing Vegetative Propagation of Two ‘Schipkaensis’ Common Cherrylaurel Ploidy Levels. HortTechnology. 2017; 27 (1):69-72.
Chicago/Turabian StyleJustin A. Schulze; Ryan N. Contreras; Carolyn Scagel. 2017. "Comparing Vegetative Propagation of Two ‘Schipkaensis’ Common Cherrylaurel Ploidy Levels." HortTechnology 27, no. 1: 69-72.
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.
Ryan N. Contreras; Luigi Meneghelli. In Vitro Chromosome Doubling of Prunus laurocerasus ‘Otto Luyken’ and ‘Schipkaensis’. HortScience 2016, 51, 1463 -1466.
AMA StyleRyan N. Contreras, Luigi Meneghelli. In Vitro Chromosome Doubling of Prunus laurocerasus ‘Otto Luyken’ and ‘Schipkaensis’. HortScience. 2016; 51 (12):1463-1466.
Chicago/Turabian StyleRyan N. Contreras; Luigi Meneghelli. 2016. "In Vitro Chromosome Doubling of Prunus laurocerasus ‘Otto Luyken’ and ‘Schipkaensis’." HortScience 51, no. 12: 1463-1466.
The genus Cotoneaster (Rosaceae, Maloideae) is highly diverse, containing ≈400 species. Like other maloids, there is a high frequency of naturally occurring polyploids within the genus, with most species being tetraploid or triploid. Apomixis is also prevalent and is associated with polyploidy. The objective of this study was to estimate genome sizes and infer ploidy levels for species that had not previously been investigated as well as compare estimates using two fluorochromes and determine base pair (bp) composition. Chromosome counts of seven species confirmed ploidy levels estimated from flow cytometric analysis of nuclei stained with 4′,6-diamidino-2-phenylindole (DAPI). Monoploid (1Cx) genome sizes ranged from 0.71 to 0.96 pg. Differences in monoploid genome size were not related to current taxonomic treatment, indicating that while chromosome sizes may vary among species, there are no clear differences related to subgeneric groups. A comparison of DAPI and propidium iodide (PI) showed a difference in DNA staining in Cotoneaster comparable to other rosaceous species. Base pair composition (AT%) in Cotoneaster ranged from 58.4% to 60.8%, which led to overestimation of genome size estimates in many cases—assuming the estimates of the DNA intercalator are accurate. Our findings will inform breeders with regard to the reproductive behavior of potential parents and may be used to confirm hybrids from interploid crosses.
Joseph J. Rothleutner; Mara W. Friddle; Ryan N. Contreras. Ploidy Levels, Relative Genome Sizes, and Base Pair Composition in Cotoneaster. Journal of the American Society for Horticultural Science 2016, 141, 457 -466.
AMA StyleJoseph J. Rothleutner, Mara W. Friddle, Ryan N. Contreras. Ploidy Levels, Relative Genome Sizes, and Base Pair Composition in Cotoneaster. Journal of the American Society for Horticultural Science. 2016; 141 (5):457-466.
Chicago/Turabian StyleJoseph J. Rothleutner; Mara W. Friddle; Ryan N. Contreras. 2016. "Ploidy Levels, Relative Genome Sizes, and Base Pair Composition in Cotoneaster." Journal of the American Society for Horticultural Science 141, no. 5: 457-466.
Ryan N. Contreras; Mara W. Friddle. ‘Oregon Snowflake’ Flowering Currant. HortScience 2015, 50, 320 -321.
AMA StyleRyan N. Contreras, Mara W. Friddle. ‘Oregon Snowflake’ Flowering Currant. HortScience. 2015; 50 (2):320-321.
Chicago/Turabian StyleRyan N. Contreras; Mara W. Friddle. 2015. "‘Oregon Snowflake’ Flowering Currant." HortScience 50, no. 2: 320-321.
Cotoneaster Medik. is a genus of ornamental landscape plants commonly affected by fire blight. Fire blight is a disease caused by the bacterial pathogen, Erwinia amylovora (Burrill) Winslow et al., that attacks a wide range of taxa in the apple subfamily (Maloideae; Rosaceae). To assess susceptibility of species and identify potential sources of resistance, we inoculated 52 taxa of Cotoneaster with E. amylovora. Disease severity was scored by percent shoot necrosis (lesion length/total shoot length). Disease screenings were conducted over 2 years and varying levels of susceptibility were observed. Some taxa were highly susceptible to fire blight and the disease resulted in whole plant mortality (C. rhytidophyllus Rehder & E.H. Wilson, C. rugosus E. Pritzel ex Diels, and C. wardii W.W. Smith). Other taxa repeatedly exhibited moderate to high levels of disease resistance [C. arbusculus G. Klotz, C. chungtinensis (T.T. Yu) J. Fryer & B. Hylmö, C. delsianus E. Pritzel var. delsianus, C. sikangensis Flinck & B. Hylmö, C. simonsii Baker, and C. splendens Flinck & Hylmö]. Ongoing studies are being conducted to determine if taxa with high levels of resistance under artificial inoculation will exhibit high levels of resistance in the field under natural disease pressure. Identifying sources of disease resistance will be useful for breeding programs to increase tolerance of these landscape plants with desirable horticultural characteristics to fire blight.
Joseph J. Rothleutner; Ryan N. Contreras; Virginia O. Stockwell; James Owen. Screening Cotoneaster for Resistance to Fire Blight by Artificial Inoculation. HortScience 2014, 49, 1480 -1485.
AMA StyleJoseph J. Rothleutner, Ryan N. Contreras, Virginia O. Stockwell, James Owen. Screening Cotoneaster for Resistance to Fire Blight by Artificial Inoculation. HortScience. 2014; 49 (12):1480-1485.
Chicago/Turabian StyleJoseph J. Rothleutner; Ryan N. Contreras; Virginia O. Stockwell; James Owen. 2014. "Screening Cotoneaster for Resistance to Fire Blight by Artificial Inoculation." HortScience 49, no. 12: 1480-1485.