Begonia Semperflorens-cultorum Research Articles

Efficient plant regeneration and Agrobacterium-mediated transformation of Begonia semperflorens-cultorum

Begonia semperflorens-cultorum, known as wax begonia, is one of the most popular Begonia species in which variable commercial cultivars have been produced. The genetic transformation technique is required for further modification of this species because introduction of some desired traits such as novel flower colors cannot be achieved by conventional breeding. Here we report the procedures of an efficient plant regeneration from leaf segment and production of transgenic plants using Begonia semperflorens-cultorum. Efficient induction of adventitious shoots was achieved when the explants were cultured on MS medium supplemented with 1.5 mg/l thidiazuron (TDZ), 0.5 mg/l α-naphthaleneacetic acid (NAA), 30 g/l sucrose and 2.5 mg/l gellan gum. Agrobacterium tumefaciens strain EHA101 containing the plasmid pIG121-Hm was used for gene transfer. The transient GUS expression was significantly increased when 10 mM MES was added to the co-cultivation medium. By culturing the infected explants under the selection pressure with 10 mg/l hygromycin (Hm), the Hm-resistant independent shoots were obtained at a frequency of 0.78 per explant. The regenerated Hm-resistant plants showed the integration of hygromycin phosphotransferase (HPT) gene into the genome and stable GUS expression, as the proof of genetic transformation. Consequently, the conditions established in this study enabled the transformation of Begonia semperflorens-cultorum. Production of transgenic plants through Agrobacterium-mediated transformation using an effective system for plant regeneration from leaf segment of Begonia semperflorens-cultorum was achieved.

Evaluation of Antitranspirants for Enhancing Temporary Water Stress Tolerance in Bedding Plants

Water stress during shipping and retailing reduces the postproduction quality and marketability of bedding plants. Antitranspirants can temporarily prevent plants from wilting by either physically blocking stomata or physiologically inducing stomatal closure, limiting transpirational water loss from leaves. The goal of this research was to evaluate the efficacy of commercially available antitranspirants on enhancing temporary water stress tolerance in bedding plants. Two physical antitranspirants [β-pinene polymer (βP) and vinyl-acrylic polymer (VP)], and three physiological antitranspirants [two sugar alcohol-based compounds (SACs) and a biologically active form of abscisic acid (s-ABA)] were applied to begonia (Begonia semperflorens-cultorum), new guinea impatiens (Impatiens hawkeri), impatiens (Impatiens walleriana), petunia (Petunia ×hybrida), african marigold (Tagetes erecta), and french marigold (Tagetes patula). Physical antitranspirants were sprayed on foliage and physiological antitranspirants were drenched to the media. All antitranspirants were applied at half (0.5×), equal to (1×), or twice (2×) the manufacturer’s recommended rate. Extended shelf life was observed when βP or s-ABA was applied. Treatment with βP increased the shelf life of impatiens and african marigold by 1 and 1.3 days compared with control plants, respectively. The application of βP at 2× was more effective at delaying visual wilting than at lower rates (0.5× and 1×) in african marigold. Applications of s-ABA delayed wilting by 1.3 to 3.7 days in all tested cultivars. The shelf lives of impatiens and petunia treated with s-ABA at 2× were extended the most by 3.7 and 3.0 days compared with control plants, respectively. A rapid reduction of stomatal conductance (gS) was observed within 4 hours of βP or s-ABA application in plants showing delayed wilting symptoms. s-ABA treatment appeared to cause marginal leaf chlorosis in impatiens, whereas application of βP damaged the opened flowers in all tested cultivars. The application of VP or SACs did not extend shelf life in any treated plants. These results suggest that foliar application of βP on selected species and treatment with s-ABA on most of species would allow bedding plants to withstand water deficit during shipping and/or retailing.

Evaluation of Eastern Redcedar Substrate in the Production of Four Annual Species

Peat moss and perlite have been major components in greenhouse substrates for over 50 years; however, shortages could occur due to restrictions from environmental concerns, fuel cost, and weather conditions. Due to these factors, research continues to seek available materials as alternative substrate components. These studies evaluated processed eastern redcedar (Juniperus virginiana L.) as an alternative substrate in the greenhouse production of four annual species: petunia (Petunia ×hybrida Juss.), annual vinca [Catharantus roseus (L.) G. Don], wax begonia (Begonia semperflorens-cultorum Hort.), and plumed cockscomb (Celosia argentea L.). Three screen sizes of hammer-milled eastern redcedar (ERC) were used including 0.64, 0.95, and 1.27 cm (0.25, 0.38, and 0.5 in). Plants were grown in peat moss amended with either 25 or 50% ERC (combinations of three screen sizes) and compared to a standard 80:20 peat:perlite mix. Plant growth was similar for petunia and vinca in 50% ERC (1.27 cm screen size) compared to those grown in 80:20 peat:perlite. Plants grown in 25% ERC were similar to plants grown in 80:20 peat:perlite mix for all species in all screen sizes. Root growth was similar to or greater for plants in substrates with 25% ERC when compared to the standard peat:perlite treatment. Amending peat with up to 25% eastern redcedar is an acceptable practice for the four annual species used in this study.

(77) Toleranceto Rhizoctonia solani and Garden Performance of Wax Begonia Cultivars

A strain of Rhizoctonia solani was isolated from wax begonia (Begonia Semperflorens-Cultorum hybrids) plants in garden evaluation trial plots. This strain was then used to test for disease tolerance in a controlled environment experiment. Inoculated plants of 12 cultivars were evaluated for disease development and the area under the disease progress curve was calculated. No plants were disease free, but `Stara White', `Stara Pink', and three colors from the Party series exhibited greater disease tolerance than `Ambassador Coral', `Ambassador Deep Rose', and two experimental varieties. `Stara White', `Party Pink Bronze Leaf', and `Party White Bronze Leaf' were more tolerant than `Cocktail Vodka', an industry standard. When the same cultivars were grown in field garden evaluation plots, `Cocktail Vodka', four colors from the Stara series, and three colors from the Party series exhibited superior garden performance and flowering ratings to `Ambassador Coral' and an experimental `Rose' cultivar. For most cultivars, garden performance was correlated to disease tolerance. However, `Cocktail Vodka' exhibited good garden performance despite having a high level of disease in the inoculation experiment, indicating that other factors may be involved in determining garden performance.

Light Intensity and Fertilizer Concentration: II. Optimal Fertilizer Solution Concentration for Species Differing in Light Requirement and Growth Rate

To evaluate the effects of increasing photosynthetic photon flux (PPF) on optimal fertilizer concentrations, we grew wax begonia (Begonia semperflorens-cultorum Hort.) and petunia (Petunia ×hybrida Hort. Vilm-Andr.) seedlings in a soilless growing medium without starter fertilizer under three PPF treatments (high, medium, and low corresponding to an average daily PPF of 23.2, 15.6, and 9.8 mol·m-2.d-1, respectively) and subirrigated with six fertilizer concentrations [electrical conductivity (EC) of 0.12, 0.65, 1.18, 1.71, 2.24, and 2.77 dS·m-1]. Compared to low PPF, shoot dry mass of wax begonia and petunia seedlings increased 2- and 3-fold, respectively, at high PPF. Fertilizer EC resulting in maximum shoot dry mass was the same (1.28 and 1.87 dS·m-1 for wax begonia and petunia, respectively) in the three PPF treatments. Shoot dry mass and leaf area of petunias decreased little at higher than optimal fertilizer EC in the three PPF treatments, while growth of begonia was inhibited at high fertilizer EC. The optimal fertilizer range, calculated as the lower and upper limits of fertilizer EC within which plant growth was not reduced by >10% as compared to the optimum EC was 0.65 to 1.71 dS·m-1 in wax begonia and 1.18 to >2.77 dS·m-1 for petunia. Compared to those grown at 1.18 dS·m-1, wax begonias grown at 1.71 dS·m-1 had similar dry mass, but were shorter in all three PPF treatments (average height reduction of 6.5%). In general, EC of the top layer of the growing medium was higher than that of the bottom layer of the growing medium, and this difference increased with increasing EC.

Light Intensity and Fertilizer Concentration: I. Estimating Optimal Fertilizer Concentrations from Water-use Efficiency of Wax Begonia

Environmental conditions and incorporation of nutrients into the growing medium can affect the fertilizer needs of bedding plants. To evaluate the effects of photosynthetic photon flux (PPF) and starter fertilizer on the fertilizer requirements of subirrigated plants, we grew wax begonias (Begonia semperflorens-cultorum Hort.) under three PPF levels (averaging 4.4, 6.2, and 9.9 mol·m-2·d-1) and four fertilizer concentrations [electrical conductivity (EC) of 0.15, 0.33, 0.86, and 1.4 dS·m-1] in a normal (with starter fertilizer, EC = 2.1 dS·m-1) and heavily leached (with little starter fertilizer, EC = 0.9 dS·m-1) growing medium. Except for shoot dry mass, we did not find any significant interactions between PPF and fertilizer concentration on any of the growth parameters. There was an interactive effect of fertilizer concentration and starter fertilizer on all growth parameters (shoot dry mass, leaf area, plant height, and number of flowers). When the growing medium contained a starter fertilizer, fertilizer concentration had little effect on growth. When the growing medium was leached before transplanting, growth was best with a fertilizer EC of 0.86 or 1.4 dS·m-1. Water-use efficiency (WUE) was calculated from 24-hour carbon exchange and evapotranspiration measurements, and used to estimate the required [N] in the fertilizer solution to achieve a target tissue N concentration of 45 mg·g-1. Increasing PPF increased WUE and the required [N] (from 157 to 203 mg·L-1 at PPF levels of 4.4 and 9.9 mol·m-2·d-1, respectively). The PPF effect on the required [N] appeared to be too small to be of practical significance, since dry mass data did not confirm that plants grown at high light needed higher fertilizer concentrations. Thus, fertilizer concentrations need not be adjusted based on PPF.

Acclimation of Wax Begonia to Light Intensity: Changes in Photosynthesis, Respiration, and Chlorophyll Concentration

Physiological acclimation of plants to light has been studied mostly at the leaf level; however whole-plant responses are more relevant in relation to crop growth. To examine the physiological changes associated with different daily light integrals (DLI) during growth of wax begonia (Begonia semperflorens-cultorum Hort.), we grew plants under DLI of 5.3, 9.5, 14.4, and 19.4 mol·m-2·d-1 in a whole-plant gas exchange system. Photosynthesis-light response curves of groups of 12 plants were determined after 25 d of growth. Physiological parameters were estimated per m2 ground area and per m2 leaf area. On a ground area basis, significant increases in dark respiration (Rd), quantum yield (α), the light compensation point (LCP), and maximum gross photosynthesis (Pg,max) were seen with increasing DLI. Variations in physiological parameters among different treatments were small when corrected for differences in leaf area. On a leaf area basis, α, LCP, and the light saturation point (LSP) did not change significantly, whereas significant increases in Rd and Pg,max were seen with increasing DLI. There was a small decrease in leaf chlorophyll concentration (6.3%, measured in SPAD units) with increasing DLI. This study indicates that wax begonias acclimate to low DLI by increasing their leaf chlorophyll concentration, presumably to more efficiently capture the available light, and to high DLI by increasing Pg,max to efficiently utilize the available light, thereby maximizing carbon gain under both situations.

Light Effects on Wax Begonia: Photosynthesis, Growth Respiration, Maintenance Respiration, and Carbon Use Efficiency

The effect of increasing daily light integral (DLI; 5.3, 9.5, 14.4, and 19.4 mol·m-2·d-1) on photosynthesis and respiration of wax begonia (Begonia semperflorens-cultorum Hort.) was examined by measuring CO2 exchange rates (CER) for a period of 25 d in a whole-plant gas exchange system. Although plant growth rate (GR, increase in dry weight per day) increased linearly with increasing DLI, plants grown at low DLI (5.3 or 9.5 mol·m-2·d-1) respired more carbohydrates than were fixed in photosynthesis during the early growth period (13 and 4 d, respectively), resulting in a negative daily carbon gain (DCG) and GR. Carbon use efficiency [CUE, the ratio of carbon incorporated into the plant to C fixed in gross photosynthesis (Pg)] of plants grown at low DLI was low, since these plants used most of the C fixed in Pg for maintenance respiration (Rm), leaving few, if any, C for growth and growth respiration (Rg). Maintenance respiration accounted for a smaller fraction of the total respiration with increasing DLI. In addition, the importance of Rm in the carbon balance of the plants decreased over time, resulting in an increase in CUE. At harvest, crop dry weight (DWCROP) increased linearly with increasing DLI, due to the increased photosynthesis and CUE at high PPF.

Modified atmosphere treatments as a potential disinfestation technique for arthropod pests in greenhouses.

Incidental transport of arthropods on plant material can be a significant mode of pest entry into greenhouses. We evaluated the use of controlled atmosphere treatments as a potential way to eliminate arthropod pests on plant propagules (i.e., cuttings or small rooted plants). Lethal exposures to CO2 or N2 were determined for common greenhouse pests including fungus gnat larvae, Bradysia sp.; green peach aphid, Myzus persicae (Sulzer); sweetpotato whitefly, Bemisia sp.; twospotted spider mite, Tetranychus urticae Koch; and western flower thrips, Frankliniella occidentalis (Pergande). We also studied the effect of pest species, life stage, and presence or absence of plants on efficacy of modified atmosphere treatments. Finally, effects of modified atmospheres on plant quality were evaluated for several bedding plant species including begonia, Begonia semperflorens-cultorum Hort. 'Cocktail Series', chrysanthemum, Dendranthema grandiflora Tzvelev., geranium, Pelargonium X hortorum L.H. Bailey, and impatiens, Impatiens wallerana Hook f., and among cultivars of geranium and chrysanthemum. Exposure for 12-18 h to >99% N2 or CO2 caused complete mortality of aphids, mites, thrips, and whiteflies. Fungus gnat larvae were more tolerant of hypoxic conditions. Adult mites and eggs were equally susceptible. For most pests, there was no difference in response to atmospheres modified by CO2 or N2. However, there was variation in response among plant species and cultivars, with effects ranging from delayed flowering to mortality. Despite the possibility of adverse effects on some plants, this work indicates that use of modified atmospheres has potential to eliminate arthropod pests on plant propagules before they are introduced into greenhouses.

Ozone Sensitivity of Selected Southeastern Landscape Plants

Abstract Twenty-six species and/or cultivars commonly used in landscapes of the southeastern United States were exposed to three ozone (O3) levels for 3-week periods during spring and summer 1994. Thirteen species or cultivars exhibited visible foliar injury at the highest rate, 2.5× ambient, and two cultivars exhibited foliar injury with ambient O3 concentrations. The most sensitive were two cultivars of buddleia or butterfly bush (Buddleia davidii Franch. ‘Black Knight’ and ‘Royal Red’), with visible injury under ambient and 2.5× ambient O3 levels, and ‘White Star’ zinnia (Zinnia angustifolia HBK ‘White Star’) with visible injury observed under 2.5× ambient O3 levels. Seven other cultivars of buddleia and three cultivars of red maple (Acer rubrum L. ‘Autumn Flame’, ‘October Glory’, and ‘Franksred’ (Red SunsetTM)) exhibited minor foliar injury under 2.5× ambient O3 levels. Visible injury was not present on flowering dogwood (Cornus florida L. ‘Stokes Pink’), hollies (Ilex crenata Thunb. ‘Green Luster’, I. cornuta Lindl. & Paxt. ‘Carissa’, I. x attenuate Ashe ‘Fosteri #2’), cultivars of crapemyrtle (Lagerstroemia indica L. ‘Byers Wonderful White’ and ‘Carolina Beauty’), glossy abelia (Abelia x grandiflora (Andre) Rehd.), southern waxmyrtle (Myrica cerifera L.), sawtooth oak (Quercus acutissima Carruth), begonia (Begonia semperflorens-cultorum Hort. ‘Pizzazz Red’), petunia (Petunia x hybrida Hort. Vilm.-Andr. ‘Celebrity Red’), salvia (Salvia splendens Sello. ‘Hotline’), or gomphrena (Gomphrena globosa L. ‘Strawberry Fields’).

Polyaxial development in homeotic flowers of three begonia cultivars

Development of staminate flowers in double-flowering Begonia semperflorens-cultorum cultivars 'Cinderella', 'Goldie Locks', and 'Lucy Lockett' was examined using epi-illumination microscopy, focussing on later stages when secondary partial floral buds formed on the floral apex. This process, switching from floral to inflorescence-like development, is an example of homeosis, the expression of inflorescence features on a floral apex. Floral development began as in a normal begonia flower with the formation of a perianth consisting of two sepals and two petals, but sepaloid and (or) petaloid appendages then developed in what corresponded to stamen positions in normal Begonia species. This was usually followed by lateral elongation, distortion of the primary floral apex, and formation of secondary partial floral buds. The pattern of primordial inception on the secondary apices tended to be irregular, but in some cases, appendage primordia formed in groups of twos, threes, and fours, and in a somewhat alternating formation on the apices. Often, primordial initiation seemed to continue on secondary apices even after anthesis of the staminate flower. Appendage primordia that formed on the secondary buds usually were laterally elongate and bifacial, giving them a phyllomic appearance. Others were, on occasion, more hemispherical at inception, but as they developed they became phyllomic. Key words: homeosis, polyaxial, floral development, intermediate inflorescence.