Flowering dogwoods ( Cornus florida L.) are relatively small deciduous trees that are popular as landscape ornamentals and native to the eastern United States and Canada. Cornus florida is classified in the red-fruited, big-bracted dogwood
effect of WD on quality characteristics such as bract color and size, and 3) compare the effects of WD on plant quality to those of PGRs. Materials and Methods Plant material and growing conditions. Poinsettia ‘Classic Red’ cuttings, rooted in phenolic
growth suppression and subsequent stunting of poinsettias as well as reduced bract size ( Faust et al., 2001 ; Lewis et al., 2004 ; Niu et al., 2002 ), whereas application of too little PGR may not sufficiently suppress stem elongation. Manipulating the
One factor in the development of poinsettia (Euphorbia pulcherrima Willd. ex Klotzch) bract necrosis is plant nutrition. Twenty poinsettia cultivars were grown as 15-cm single-pinched plants in Metro mix 510 with standard commercial practices for irrigating, fertilizing, and pest control. Seventy days after initial anthesis, plants were harvested and the number of necrotic and healthy bracts recorded. Mineral nutrients in bract margins were determined. The only nutrient that had a significant relationship to incidence of bract necrosis across the 20 cultivars was bract B content (R 2=49.5%, P< 0.001). This suggests that cultivars with lower bract B content are more susceptible to bract necrosis. Using `Supjibi' plants grown in the Metro mix 510, we applied topical sprays of B (0, 4, or 8 mm) weekly during bract development or once at initial anthesis (8 mm). Also a weekly drench treatment of B (10 mm) was applied initially at bract color change and continued for 2 more weeks. By 42 days after initial anthesis, all B treatments averaged together reduced incidence of bract necrosis from 33.1% for controls to 10% for plant receiving B treatment. The B drench treatment resulted in leaf scorching and there was some leaf tipburn with the 4 and 8 mm B weekly sprays. The single spray (8 mm B) treatment at initial anthesis caused no injury. Although B sprays are not a replacement for Ca sprays as a control for bract necrosis, the results suggest a role for B in the etiology of bract necrosis.
Abstract
High-performance liquid chromatographic (HPLC) procedures for the separation of flavonoids in poinsettia bracts are described. Anthocyanins present were cyanidin 3-galactoside, and the 3-glucosides and 3-rutinosides of cyanidin and pelargonidin. Flavonols present were 3-rhamnosylgalactosides, 3-rhamnosylgluco-sides, 3-galactosides, 3-glucosides, and 3-rhamnosides of quercetin and kaempferol. The use of these chemical markers along with the classical methods for plant identification should help resolve the difficulties of describing new cultivars protected by the plant patent law.
Abstract
Foliar-bract calcium (Ca) sprays and fertilization practices that altered Ca availability and supply were evaluated for their effect on marginal bract necrosis incidences of ‘Gutbier V-14 Glory’ poinsettia (Euphorbia pulcherrima Willd.). About 90% fewer marginal necrotic lesions were observed on plants receiving an 81% NO3-N and 903-ppm Ca soluble fertilizer with 10% of the total nutrients foliar-applied than on plants grown with medium-applied Osmocote 19N-2.6P-10K (47% NO3-N) or with medium-applied liquid fertilizer containing 30% or 65% NO3-N and 0 ppm Ca. Addition of 354 ppm Ca in a 53% NO3-N, or 964 ppm Ca in a 75% NO3-N medium-applied fertilizer did not significantly reduce the number of lesions compared to the same fertilizer with 0 ppm Ca or the equivalent rate of a 53% NO3-N Osmocote 14N-6.1P-11.6K. Weekly foliar-bract sprays of 432 ppm Ca from Ca(NO3)2·4H2O reduced numbers of lesions by 94% (<1.5 lesions per plant), regardless of fertilization practice. Thus, soil applications of Ca were not effective in preventing marginal bract necrosis, whereas foliar applications of Ca were highly efficacious.
The early onset of bract necrosis in poinsettia (Euphorbia pulcherrima Willd. ex. Klotzch) is characterized by small dark-stained spots that precede the development of enlarged necrotic lesions. Electron micrographs of adaxial epidermal and subepidermal tissues with early symptoms of necrosis revealed large, electron-dense deposits in cell vacuoles. These spherical bodies resembled condensed tannins observed in the epidermal tissues of peach and apple fruit. Chemical analysis of bract tissues confirmed the presence of condensed tannins. Furthermore, there were higher concentrations of condensed tannin in bract samples with 2-mm-diameter lesions than in samples with lesions <0.5 mm (equivalent to catechin concentrations of 59 and 13 mg·g-1 fresh mass, respectively). No tannin bodies were observed in parallel samples of healthy-appearing bracts in which only trace concentrations of condensed tannins were measured (0.2 mg·g-1 fresh mass). The evidence suggests an association between condensed tannin accumulation in localized areas of the bract and the early appearance of bract necrosis symptoms.
Bract edge burn (BEB) has been observed in different greenhouse operations across North America over the past 10 years. The symptoms develop at anthesis or shortly after shipping. Varieties such as `Supjibi', `V-14 Glory', and `Celebrate 2' are considered susceptible cultivars. A number of trials using endosulfan (Thiodan) have been conducted. In 1993, `Supjibi' branched poinsettias were sprayed with either Thiodan, Decis, Thiodan + Decis, or water or remained unsprayed. The sprays were applied in week 39, 42 or 45. For each treatment period, plants were treated three times at 4-day intervals at label recommendations. At anthesis (week 47), plants sprayed with Thiodan or Thiodan + Decis during week 39 showed necrosis in the margin of the transitional bracts. In 1994, single spray applications in week 39, 40, 41, 42, or 45 of Thiodan, Ca (400 ppm), Thiodan + Ca in a tank mix, unsprayed, or Thiodan followed by four calcium sprays (weekly) in November. At week 48, all treatments except the latter showed necrosis, except this time it was marginal flecking in the transitional or primary bracts. In Spring 1995, single vs. multiple Thiodan applications were compared.
`V-14 Glory' poinsettias in 15-cm pots were pinched on 24 Sept. and given long days until 8 Oct. Chemical treatments were paclobutrazol drench, paclobutrazol spray, or daminozide/chlormequat (D/C) spray. Time of application was between 8 Oct. and 12 Nov. Heights ranged between 27 and 31 cm. D/C reduced bract size more than paclobutrazol spray, and for both, later treatments had greater affect. Paclobutrazol drench did not have a significant affect.
A second experiment had two cultivars, `Freedom' and `V-14'; three paclobutrazol concentrations, 0.2, 0.3 or 0.4 mg per pot; and three application times, 30 Sept., 14 Oct. or 28 Oct. Treatment on 30 Sept. produced the smallest bracts. The cultivar × concentration interaction was significant with 0.4 mg reducing bract size for `Freedom' but not `V-14'. Treatments on 28 Oct. had less effect on height than the other two dates. `Freedom' were shorter than `V-14'. and higher concentrations had more effect on `Freedom' than `V-14'.
Incidences of poinsettia (Euphorbia pulcherrima Willd. ex Klotzch) bract disorders like the pathogen Botrytis cinerea and the abiotic disorder bract necrosis are related to nutrient stress. `Supjibi' poinsettias were grown hydroponically with four Ca-B combinations of 0 or 4 mm Ca added with either 5 or 120 μmol B added. Forty-one days after initial anthesis, plants were harvested and their bracts subdivided into true-bracts and transitional-bracts for determination of incidence of botrytis lesions and bract necrosis. Mineral nutrients in bract margins were determined for leaves, transitional-bracts and true-bracts. Leaf margins had the highest concentrations of Ca and B. Margins of transitional-bracts had substantially lower concentrations and margins of true-bracts the least. The low Ca (0 mm) or low B (5 μmol) treatments greatly reduced the concentrations of these elements, respectively, in all three tissue types. The low Ca-low B treatment increased the incidence of bract necrosis on true-bracts from 1.9% on controls (4 mm Ca, 120 μmol B) to 27%. Low Ca treatment increased bract necrosis on transitional-bracts from 1.6% on controls to 24.3%. Bract necrosis incidence was the same on true-bracts and transitional-bracts, whereas the incidence of botrytis was higher on transitional-bracts than on true-bracts. Botrytis incidence was increased for true-bracts and transitional-bracts by plant exposure to low Ca solutions compared to plants in 4 mm Ca. Low Ca reduced growth in roots, but not shoots. Ca and B stress to roots increased the incidence of bract necrosis on true-bracts, while only Ca stress increased incidence of botrytis.