Search Results
You are looking at 31 - 40 of 49 items for
- Author or Editor: Ryan Contreras x
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.
‘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.
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).
Wide hybridization can lead to recombination of diverse traits and creation of unique phenotypes, but the resultant hybrids are often sterile as is the case with the intersubgeneric hybrid Rhododendron L. ‘Fragrant Affinity’. Sterility in wide hybrids can either be genic or chromosomal; the latter may be overcome by induction of polyploidy, which can restore chromosome homology and fertility. Cytologic studies of ‘Fragrant Affinity’ appear to support the presence of bridges between bivalents in metaphase I and laggard chromosomes in anaphase I. In the current study, an allotetraploid form of R. ‘Fragrant Affinity’ was developed using oryzalin (4-(dipropylamino)-3, 5-dinitro-benzenesulfonamide) as a mitotic inhibitor and chromosomal doubling agent. Genome sizes (2C) were determined using flow cytometry and found to be ≈1.6 and 3.2 pg for the diploid and allotetraploid, respectively. 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 used as a pistillate parent when pollinated with pollen from viable diploid and tetraploid parents. The allotetraploid produced viable seeds and seedlings when pollinated with pollen from either diploid or tetraploid parents, including self-pollination, demonstrating restored male and female fertility.
Japanese-cedar [Cryptomeria japonica (L.f.) D. Don] represents an alternative to leyland cypress [×Cuprocyparis leylandii (A.B. Jacks. & Dallim.) Farjon] as an evergreen screen or specimen plant for landscapes. It performs well under a range of soil and environmental conditions but has been underused attributable, in part, to unsightly winter browning caused by photoinhibition. In previous studies, chance seedlings that did not exhibit winter browning were identified as tetraploids. The current study was conducted to induce polyploidy in japanese-cedar. Approximately 600 seedlings were sprayed with 150 μM oryzalin + 0.1% SilEnergy™ for 30 consecutive days under laboratory conditions. Two hundred thirty-seven seedlings with thickened and twisted leaves were selected, transplanted, and grown in a glasshouse for 120 days. Seedling ploidy levels were analyzed using flow cytometry 180 days after treatment (DAT), identifying 197 (83.1%) tetraploids, 22 (9.3%) cytochimeras, and 18 (7.6%) diploids. Morphology of induced tetraploids was similar to that previously described and provided a phenotypic marker during selection that was over 92% accurate. A random subset of 20 tetraploid individuals was analyzed 270 DAT and were found to contain only tetraploid cells in the leaves analyzed, confirming stability over this period. This study demonstrated the use of oryzalin for inducing tetraploids in japanese-cedar, which we predict will be effective in other gymnosperms.
As the industrial hemp (Cannabis sativa L.) market grows, there is a need for methods to clonally propagate parental breeding stock and new cultivars. Information is lacking on vegetative cutting propagation of hemp. We evaluated how propagation environment (intermittent mist vs. subirrigation under a humidity dome), indole-3-butyric acid (IBA) formulation (talc rooting powder vs. IBA in solution), and IBA concentration (0, 3000, or 8000 ppm) affected stem cuttings from ‘I3’, a cannabinoid-free cultivar of industrial hemp. Under mist or domes, rooting quality and percent declined at 8000 ppm IBA. Root and shoot quality and rooting percentage also were reduced in 3000 ppm IBA in solution treatment compared with talc. Our data show that for the cultivar tested, cuttings rooted at the highest percentage and produced the highest-quality roots and shoots with either no hormone or 3000 ppm talc powder. These treatments did equally well under humidity domes or intermittent mist.
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.
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.
New technologies such as online databases, interactive dichotomous keys, and online courses have changed the way some plant identification courses are delivered. These changing resources may create discrepancies between traditional instruction of landscape plant materials courses and the way modern students learn, which may result in students not meeting their potential. However, what resources students are using to study plant materials is unclear. We investigated the relationship between learning styles, study habits, and performance of students during two terms of woody landscape plant materials courses. To assess these relationships, we determined the characteristics of the participants and their preferred study method throughout the duration of the term as well as correlations between 1) preferred learning styles and performance, 2) preferred learning styles and preferred study method, and 3) performance and preferred study method. The participants in this study (n = 31) consisted of 14 males and 17 females. Of the 31 participants, 3 were freshmen, 3 were sophomores, 16 were juniors, 7 were seniors, and 2 were graduate students. Based on preference scores for learning style, 15 students were identified as visual learners, 3 as auditory, and 13 as kinesthetic learners. No significant relationships were observed between preferred learning style and performance or between preferred learning style and preferred study method. The two preferred study methods were using branch samples collected by the instructor and notecards created by students. No relationship existed between preferred study method and performance in the course. Our study provides information on study methods of woody plant identification students enrolled in a site-based course. We did not observe statistically significant relationships among preferred learning style, preferred study method, and course grade, but anecdotal evidence indicated students who prepared their own study aids by making notecards scored better in these courses.
Morphological analysis historically has been used to determine parentage of unknown hybrids. This can be difficult when potential parents have similar appearance, as in the case of three azaleodendron cultivars, Rhododendron L. ‘Fragrans’, ‘Fragrans Affinity’, and ‘Fragrant Affinity’. These cultivars are similar in name and appearance, and all are purported hybrids of R. catawbiense Michx. or R. ponticum L. and R. viscosum (L.) Torr. Amplified fragment length polymorphism (AFLP) analysis was conducted to determine whether the cultivars are synonyms or distinct clones and to elucidate the parental species. The three cultivars, suspected to be hybrids between taxa in subgenera Hymenanthes (Blume) K.Koch (evergreen rhododendrons) and Pentanthera (G.Don) Pojarkova (deciduous azaleas), and related taxa from each subgenus were evaluated using 31 AFLP primer combinations. Genetic similarity, calculated using Jaccard's coefficient, among the hybrids ranged from 53% to 71%, indicating that they are distinct cultivars and not a single clone. Genetic similarity was highest between the hybrids and R. ponticum among the evergreen rhododendrons, and R. viscosum among the deciduous azaleas. A dendrogram generated using the genetic similarity matrix grouped taxa into their respective subgenera, with the three cultivars nested intermediately between subgenera but more closely with subgenus Hymenanthes and particularly R. ponticum, suggesting it is the evergreen rhododendron parent. Furthermore, principle components grouped R. ponticum more closely with the hybrids and there were 18 AFLP fragments unique to R. ponticum and the hybrids. However, no unique AFLP bands were shared exclusively among the hybrids and the purported deciduous azalea parent, R. viscosum, suggesting that the original azalea parents may have been hybrids.