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  • Author or Editor: Hazel Wetzstein x
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Georgia plume (Elliottia racemosa) is a threatened woody plant endemic to the Coastal Plain region of Georgia in the southeastern United States. Seed set is low in most populations, and sexual recruitment has not been observed in recent times. The objective of this study was to describe the floral biology of georgia plume. which is fundamental information needed to develop an understanding of the causes for lack of sexual reproduction in natural populations. Floral development was characterized and morphological characteristics at key developmental stages ranging from small, unopened buds to open flowers with receptive stigmas were examined using light and scanning electron microscopy. Flowering is protandrous, and anthers dehisce releasing pollen within closed buds before stigmas are receptive. Pollen tetrads, aggregated by viscin strands, are presented on unreceptive stigmas when petals reflex. Receptive stigmas developed a raised and lobed central region with a clefted opening leading to a stylar canal containing exudate produced in secretory regions. Receptivity of the non-papillate stigma is indicated by the formation of an exudate droplet, which is formed within 1 day after flower opening. Pollen viability was low to moderate; tetrad germination ranged from 20% to 40% using in vitro germination assays indicating poor pollen quality and may contribute to lack of seed development in some populations. No developmental abnormalities in stigmas or styles were observed indicating other factors are responsible for lack of sexual recruitment in the wild.

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Pomegranate trees (Punica granatum) produce large numbers of both hermaphroditic (bisexual) flowers that produce fruit and functionally male flowers that characteristically abort. Excessive production of male flowers can result in decreased yields resulting from their inability to set fruit. Within hermaphroditic flowers, sex expression appears to follow a spectrum ranging from those exhibiting strong to weak pistil development. Unknown is the scope that flower quality plays in influencing fruit production. A description of floral characteristics and how they vary with flowers of different sizes and positions is lacking in pomegranate and was the focus of this study. Furthermore, the effects of flower size and position on fruit set and fruit size were evaluated. This study documents that flower size characteristics and ovule development can be quite variable and are related to flower type and position. Single and terminal flowers within a cluster were larger than lateral flowers. In addition, lateral flowers exhibited a high frequency of flowers with poor ovule development sufficient to negatively impact fruiting in that flower type. Ovule numbers per flower were significantly influenced by flower size with more ovules in larger flowers. Pollination studies verified significantly higher fruit set and fruit weight, and larger commercial size distributions were obtained with larger vs. smaller flowers. Thus, flower quality is an important issue in pomegranate. Cultural and environmental factors that influence flower size and vigor may have a direct consequence on fruit production and yield.

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Abstract

The anatomy of in vitro- and in vivo-developed leaves of sweetgum, Liquidambar styraciflua L., grown under three quantum fluxes (PPF), was evaluated using light and scanning electron microscopy. Leaf characteristics of both in vitro- and in vivo-developed plants were modified by light: high irradiance was associated with more compact mesophyll and larger cells than low irradiance. However, when compared to plants grown in vivo under corresponding irradiance levels, all plants grown in vitro had smaller, thinner leaves and smaller mesophyll cells lacking extensive vacuolar components. Leaves developed in vitro had larger, raised stomata regardless of light level and, except at the highest irradiance, exhibited significantly greater stomatal densities than in vivo-developed leaves.

Open Access

Propiconazole, a triazole fungicide, has been reported to inhibit leaf expansion in pecan [Carya illinoensis (Wangenh.) K. Koch] trees when applied under field conditions. This study was conducted to determine the effect of propiconazole on pecan leaf morphology and structure using light and transmission electron microscopy. Mature pecan trees were sprayed once or three times per week from budbreak to pollen maturity. Fungicide sprays resulted in significantly reduced leaf area. Compared to controls, leaves from propiconazole-treated shoots had alterations in cell arrangement characterized by more tightly packed palisade parenchyma cells with fewer intercellular spaces; neither leaf thickness nor palisade or spongy layer thickness were affected. Propiconazole caused modifications in the chloroplasts, with a tendency for internal membranes to be less defined, and for thylakiods to exhibit less stacking. The extent of structural changes was related to fungicide dosage. Results show that propiconazole applications during leaf development can inhibit leaf expansion and modify cellular organization of the mesophyll cells. Chemical name used: 1-[[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl] methyl]-1H-1,2,4-triazole (propiconazole).

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Abstract

Tissue cultures of pecan [Carya illinoensis (Wangenh.) C. Koch] were initiated from embryo explants collected weekly from 12 weeks post-pollination until fruit maturity. Three cultures derived from immature embryos collected 14 weeks postpollination produced primary somatic embryos within 1 month following transfer from modified woody plant medium (WPM) with 2.0 mgliter−1 2,4-D and 0.25 mg liter−1 BA in the light to hormone-free medium in the dark. Scanning electron microscopy documented the development of secondary embryos, which followed a globular, heartshaped, and torpedo-stage developmental sequence. Chemical names used: (2,4-di-chlorophenoxy) acetic acid (2,4-D), N-(phenylmethyl)-1H-purin-6-amine (BA), and 1H-indole-3-butanoic acid (IBA).

Open Access

Abstract

It is increasingly evident that the concentration and type of matrix used in nutrient media can profoundly influence the response of tissues cultured in vitro. Picea abies shoot cultures exhibited increased dry weight yields (4) and increased shoot growth (9) with decreasing agar concentrations. Singha (5) compared shoot proliferation of crabapple and pear in Phytagar concentrations ranging from 0% to 1.2%. Optimal proliferation and growth occurred in crabapple on 0.3% agar, with higher concentrations decreasing these growth characteristics. In pear, increasing agar concentration also decreased shoot growth, but shoot proliferation was greatest at 0.6% or higher agar concentrations. Rooting has been promoted without or with lower agar concentrations in grape (1), Norway spruce (9), and apple (10). However, vitrification (glassiness or waterlogging) has been shown to increase with lower agar concentrations (9) and limits the use of liquid culture in some species.

Open Access

Abstract

The cotyledons of pecan [Carya illinoensis (Wang.) K. Koch] seed remain fleshy and turgid throughout an attachment period of several weeks after germination. The growth (dry weight) of the developing seedling was dependent on the cotyledons for the first 3 weeks of the 6–10 week attachment period.

Open Access

Accurate mapping, inventory assessment, and habitat descriptions are critically important for the development of plant conservation strategies of rare plants. Georgia plume, Elliottia racemosa (Ericaceae), is a rare threatened plant endemic only to the state of Georgia. In this study, census and distribution data were collected and the ecological habitat characterized for all known populations of georgia plume using geographic information system/global positioning system (GIS/GPS)-based methods. Causes for population losses and decline were assessed by evaluating both extant populations and historically reported but currently inactive sites. Landowner permission was obtained to visit 56% (32 of 57) of all known recorded populations. Over 40% of visited locations no longer contained georgia plume; 58% of inactive sites were associated with anthropogenic disturbances including farming and timber. Populations not visited by ground were evaluated using aerial photographs: of 29 putative populations, 66% were judged highly unlikely to contain georgia plume based on current land use. Census data verified that many populations have few individuals: 75% contained less than 45 individuals; over one-third contained 12 or fewer individuals. Over 80% of extant populations had an area of less than 0.3 ha. Field and aerial assessments of recent and historically noted populations confirm that georgia plume has disappeared from many previously reported locations and that fewer than two dozen populations may remain.

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Effects of autoclaving volume, gelling agent (Bactoagar, Gel-gro, Phytagar), and basal salts [Murashige and Skoog (MS); Woody Plant Medium (WPM); Gamborg B5 (GB)] on gel strength and pH of tissue culture media were tested. Gel strength was significantly affected by gelling agent and basal medium. MS media were generally softer than comparable WPM or GB media. As the vessel volume during autoclaving decreased, gel strength significantly decreased with Phytagar and Bactoagar gelling agents; Gel-gro had greater gel strength at the intermediate volume of medium autoclave. In all cases, autoclaving resulted in a pH decrease of 0.2 to 0.5 pH units. Lower pH values were associated with softer gels. The type of gelling agent did not greatly affect the postautoclave pH; mean values among gelling agents were within 0.05 pH units. Postautoclave pH of MS medium was lower than that of WPM or GB. This study verifies the need to observe uniform sterilization protocols to maintain consistency in the chemical and physical properties of media.

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A simple and efficient protocol is reported for the isolation of RNA from embryos and leaves of pecan [Carya illinoinensis (Wangenh.) K. Koch]. The method relies on suppression of the polyphenols from interaction with the RNA and their rapid removal from the homogenate by chloroform extraction. This method produced abundant amounts of high-quality RNA. This protocol is likely to be useful for Juglandaceous species and other recalcitrant plants with high levels of phenolic compounds.

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