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Dinum Perera and Brian W. Trader

Slow growth rate of plantlets, few micro-shoots per explant, and slow root growth rate are restrictions of in vitro propagation of poinsettia (Euphorbia pulcherrima Willd. ex Koltz). The purpose of this research was to develop an efficient in vitro proliferation technique for poinsettia ‘Prestige™ Red’. Explants (apical buds and axillary buds) placed on Murashige and Skoog (MS) basal medium containing only 6-benzylaminopurine (BA) and combinations of BA and indole-3-acetic acid (IAA) mostly produced red callus, which is productive and some white and gray–green calluses at the base of plantlets after 1 month, whereas explants in a medium without plant growth regulators (PGRs) produced no callus. Addition of IAA into the rooting medium increased rooting efficiency; plantlets grown in half-strength MS salts and vitamins with 28.5 μM IAA initiated rooting 11 days earlier than the plantlets grown with no PGRs. Optimization of PGR concentrations during poinsettia micropropagation helped resolve previous restrictions of in vitro poinsettia proliferation. Chemical names used: 6-benzylaminopurine (BA); indole-3-acetic acid (IAA)

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Brian W. Trader, Richard E. Veilleux, and Holly L. Scoggins

The genus Astilbe (Saxifragaceae) comprises about 13 species and is ranked consistently among the top 10 landscape perennials. Through extensive hybridization, selection and marketing, the lineage of many Astilbehas been lost. Subdioecious Astilbebiternatais the only species in the genus native to North America while other members of the genus are endemic to Asia and monoecious. Due to the unusual geographic distribution of the species and the variation in floral development among them, development of genetic markers using single nucleotide polymorphisms (SNPs) would confirm phylogenetic relationships and establish lineage within the genus. Astilbespecies, hybrids, and cultivars were obtained from plant nurseries and botanical gardens across the country. To elucidate relationships among the genus, we conducted phylogenetic analysis of DNA sequences of the chloroplast gene matKand the internal transcriber spacer (ITS) of ribosomal rDNA genes. DNA was extracted, and gene primers trnK3914 and trnK2R were used to amplify matK, and primers 1406F and ITS2 were used to amplify the ITS1 region between 18S and 5.8S ribosomal DNA units. Both matKand ITS were sequenced for each plant specimen and sequences were aligned to identify nucleotide diversity and detect SNPs. Variation in nucleotide sequence for either gene yielded similar dendrograms. Nucleotide variation among the Astilbeutilized in this study has allowed the development of SNP markers that may be useful for fingerprinting unknown hybrids or cultivars in the industry, and may be used for species alignment within the genus.

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Brian W. Trader, Holly L. Scoggins, and Richard E. Veilleux

The genus Astilbe (Saxifragaceae) is comprised of approximately 20 species and is ranked consistently among the top ten landscape perennials. Through extensive hybridization, selection, and marketing, the lineage of many Astilbe has been lost. Subdioecious Astilbe biternata is the only species in the genus native to North America, while other members of the genus are endemic to Asia and monoecious. Due to the unusual geographic distribution of the species and the variation in floral development among them, investigation of morphological characters may help establish lineage within the genus. Herbarium material representing described species and varieties of Astilbe was acquired from several herbaria nationwide. Twenty-seven character states were selected to help distinguish members among the genus. Morphological character states chosen for inferring differences among species in Astilbe varied from degree of pubescence to leaf branching with an emphasis on floral characteristics such as sepal and petal variation. Character state matrix was assimilated for 20 taxa of Astilbe and analyzed using maximum parsimony. The monotypic genus Saxifragopsis was utilized as the outgroup taxa. Resulting phylogenetic trees show Astilbe simplicifolia as the species from which all members of the genus were derived. The American species, Astilbe biternata, separated away from other members within the genus. There is evidence from the phylogeny based on the morphological character states that some described species may actually represent variation within populations of species. Combination of this morphological data with molecular sequence information may be informative for further description of the Astilbe genus.

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Brian W. Trader*, Hope A. Gruszewski, Norman I. Barclift, Richard E. Veilleux, and Holly L. Scoggins

Coreopsis grandiflora (tickseed) regenerates readily from leaf segments allowing the possibility to exploit somaclonal variation as a means to develop novel phenotypes. We used true leaves from in vitro seedlings of Coreopsis grandiflora `Domino' grown on MS basal medium as explants in a series of experiments to evaluate the effect of media, leaf explant orientation, and genotype on shoot regeneration. Genotype accounted for most of the variation with two particular seedlings regenerating freely and eight others generally recalcitrant. From these two seedlings, designated E2 and H2, shoots were regenerated and acclimated to the greenhouse over a period of weeks. Once the plants had established (≈6 weeks after acclimatization) they were vernalized by moving them to a lighted bench (12-h photoperiod) in a walk-in cooler at 4 °C .On transfer back into the greenhouse, the plants flowered within a few weeks; 15 of 175 somaclones were selected based on distinct differences in flower orientation and appearance. The selected somaclones were propagated by division and transplanted to the field in May 2002 in a randomized complete-block design with three-plant plots and three replications, to determine if the novel characteristics persisted through an additional propagation cycle. In the field, plant height, leaf dimension, flowering, and flower dimensions were scored in June-July 2003. Significant differences were found between somaclones and the original E2 and H2 similarly propagated seedlings for desirable (more petals per flower, greater flowering, shorter plants), undesirable (less flowering, smaller flowers), and neutral (narrower leaves, taller plants) traits.

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Brian W. Trader, Hope A. Gruszewski, Holly L. Scoggins, and Richard E. Veilleux

Coreopsis species (tickseed) can be regenerated from leaf segments allowing the possibility to exploit somaclonal variation as a means to develop novel phenotypes. We used true leaf explants from in vitro seedlings of perennial C. grandiflora (A. Gray) Sherff `Domino' and `Sunray' grown on Murashige and Skoog (MS) basal medium. Two of ten seedlings of `Domino' regenerated freely and others were generally recalcitrant. From these two seedlings, designated E2 and H2, shoots were regenerated and acclimatized to the greenhouse. About 175 plants were established and vernalized from which somaclones were selected based on distinct differences in flower orientation and appearance. The selected somaclones were propagated by division and transplanted to the field in August 2001 in a randomized complete block design with three-plant plots and three replications to determine whether novel characteristics persisted through an additional propagation cycle. In the field, plant height, leaf dimension, flowering, and flower dimensions were scored in June and July 2003. Differences were found between somaclones and similarly propagated E2 and H2 for desirable (more petals per flower, greater flowering, shorter plants), undesirable (less flowering, smaller flowers), and neutral (narrower leaves, taller plants) traits. Open-pollinated (OP) seed was collected and germinated and the seedlings from somaclones that differed significantly from E2 and H2 were evaluated. These maternally selected seedlings were overwintered then planted in the field in May 2004. Most traits that differentiated somaclones from E2 and H2 did not persist in the OP seedling population; however variation that was likely introduced through outcrossing resulted in desirable phenotypes with potential for new cultivar development.

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Bandara Gajanayake, Brian W. Trader, K. Raja Reddy, and Richard L. Harkess

Temperature affects reproductive potential, aesthetic, and commercial value of ornamental peppers (Capsicum annuum L.). Limited information is available on cultivar tolerance to temperature stress. An experiment was conducted using pollen and physiological parameters to assess high and low temperature tolerance in ornamental peppers. In vitro pollen germination (PG) and pollen tube length (PTL) of 12 morphologically diverse ornamental pepper cultivars were measured at a range of temperatures, 10 to 45 °C with 5 °C increments. Cell membrane thermostability (CMT), chlorophyll stability index (CSI), canopy temperature depression (CTD), and pollen viability (PV) were measured during flowering. From the modified bilinear temperature–PG and PTL response functions, cardinal temperatures (Tmin, Topt, and Tmax) for PG and PTL and maximum PG (PGmax) and PTL (PTLmax) were estimated. Cultivars varied significantly for PG, PTL, cardinal temperatures for PG and PTL, and all three physiological parameters. Cumulative temperature response index (CTRI) of each cultivar, calculated as the sum of 12 individual temperature responses derived from PV, PGmax, PTLmax, Tmin, Topt, and Tmax for PG and PTL, CMT, CTD, and CSI were used to distinguish differences among the cultivars and classify for high (heat) and low (cold) temperature tolerance. Based on CTRI–heat, cultivars were classified as heat-sensitive (‘Black Pearl’, ‘Red Missile’, and ‘Salsa Yellow’), intermediate (‘Calico’, ‘Purple Flash’, ‘Sangria’, and ‘Variegata’), and heat-tolerant (‘Chilly Chili’, ‘Medusa’, ‘Thai Hot’, ‘Explosive Ember’, and ‘Treasures Red’). Similarly, cultivars were classified for cold tolerance as cold-sensitive, moderately cold-sensitive, moderately cold-tolerant, and cold-tolerant based on CTRI–cold. ‘Red Missile’ and ‘Salsa Yellow’ were classified as cold-tolerant. Cultivar screening using pollen parameters will be ideal for reproductive temperature tolerance, whereas physiological parameters will be suitable for screening vegetative temperature tolerance. The identified heat- and cold-tolerant cultivars are potential candidates in breeding programs to develop new ornamental and vegetable pepper genotypes for high and low temperature tolerance.

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Andrea N. Brennan, Valerie C. Pence, Matthew D. Taylor, Brian W. Trader, and Murphy Westwood

Tissue culture using mature-phase plant material is a useful tool for species conservation, but can be a challenge with oak (Quercus) species, often resulting in low growth and survival. Two different tissue culture media were compared and used to determine whether there was a survival, growth, or contamination response pattern in species representing three North American oak taxonomic sections: red oaks (section Lobatae), white oaks (section Quercus), and golden oaks (section Protobalanus). Mature phase cuttings were harvested in springtime from 12 oak species: arkansas oak (Q. arkansana), canby oak (Q. canbyi), slender oak (Q. graciliformis), nuttall oak (Q. texana), boynton sand post oak (Q. boyntonii), california scrub oak (Q. dumosa), engelmann oak (Q. engelmannii), gambel oak (Q. gambelii), canyon live oak (Q. chrysolepis), palmer oak (Q. palmeri), island oak (Q. tomentella), and huckleberry oak (Q. vacciniifolia). Excised shoot-tip explants were placed onto either Lloyd and McCown woody plant (WP) medium or Gresshoff and Doy (GD) medium. More growth responses and longer survival times were seen on explants grown on the WP medium than GD medium. Explants originating from species native to xeric habitats or those with smooth, glabrous young leaves had significantly higher contamination rates. Although no significant differences were found when grouped by taxonomic section, survival, growth, and contamination varied significantly by species. These findings contribute to the process of establishing tissue culture methods using mature oak material, particularly in relation to medium selection and sterilization protocols, which is critical to the conservation of this iconic group of species.

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Gregory R. Armel, Robert J. Richardson, Henry P. Wilson, Brian W. Trader, Cory M. Whaley, and Thomas E. Hines

Field and greenhouse studies were conducted in 2001 and 2002 near Painter, VA, to determine the level of weed control and pepper (Capsicum annuum) tolerance to postemergence applications of the acetolactate synthase (ALS) inhibitors trifloxysulfuron, halosulfuron, sulfosulfuron, cloransulam, and tribenuron. Based on measurements of visual injury, heights, dry weights, and chlorophyll content of pepper, the safest ALS inhibitor to pepper was trifloxysulfuron followed by halosulfuron, cloransulam, sulfosulfuron, and tribenuron. In addition, trifloxysulfuron was the only herbicide that provided greater than 86% control of pigweed species (Amaranthus spp.) and carpetweed (Mollugo verticillata) in both years of the field study. Trifloxysulfuron was also the only herbicide evaluated that did not reduce pepper yield compared with the control in both years of the field study.