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  • Author or Editor: Hazel Wetzstein x
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Fruit set of rabbiteye blueberries (Vaccinium ashei Reade) can be pollen-limited under certain conditions. The objective of this study was to determine production, release, and viability of pollen, as well as pollen-ovule ratios in the rabbiteye blueberry cultivars Austin, Brightwell, Climax, and Tifblue. In vitro tetrad germination varied among genotypes, although, values were high (≥80%) in all cultivars. Pollen viability does not seem to contribute to reproductive failure in the cultivars studied. Total pollen production per flower averaged 8434 tetrads across all cultivars. On a per ovule basis, pollen production was very low relative to other xenogamous species. The low pollen-ovule ratio of rabbiteye blueberry (≈400) may be an indicator of the high efficiency of its pollen dispensing mechanism. Total pollen production varied among cultivars. Furthermore, a significant difference in pollen release was found between two cultivars with similar total pollen production per flower. The possible mechanism regulating pollen release in these cultivars is discussed.

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Field evaluations were conducted of pecan [Carya illinoinensis (Wangenh.) C. Koch] trees regenerated via somatic embryogenesis to assess if the trees maintained clonal fidelity and exhibited true-to-type characteristics. Phenotypic and molecular comparisons were made of trees from two different tissue culture lines after 4 years in the field. Factors evaluated included shoot growth, leaf morphology, and susceptibility to fungal scab [Cladosporium caryigenum (Ellis & Langl.) Gottwald] and southern pecan leaf phylloxera (Phylloxera russellae Stoetzel). Genetic fidelity was examined using amplified fragment length polymorphism (AFLP) analysis. Statistically significant differences were observed between the culture lines in phenotypic leaf characteristics (i.e., specific leaf weight and leaf length-to-width ratio), number of shoots per 1-year-old branch, and in the frequency of scab lesions on leaves. No between-line differences were observed in trunk caliper, average and total shoot growth, shoot length per cross-sectional area, or presence of phylloxera galls. AFLP analysis readily detected differences between culture lines. Cluster analysis generally grouped trees together that were regenerated from the same line. Trees within a culture line usually exhibited similar leaf characteristics, but not shoot growth or tree height. A few trees exhibited more extreme leaf characteristics and differed from each other. However, they were statistically similar to most of the other trees in the population evaluated. AFLP data revealed that some trees exhibited greater divergence and less similarity than other trees from the same line. The nature and significance of such variation at this time are not related to any detectable phenotypic differences.

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Rabbiteye blueberry (Vaccinium ashei Reade) often exhibits problems with low fruit set. Little is known about the duration of flower receptivity in this species. The objective of this study was to investigate the effects of flower age at pollination on fruit set, seed number per fruit, and stigmatic receptivity. `Brightwell' and `Tifblue' rabbiteye blueberry plants were kept under controlled conditions in a growth chamber. Day/night temperatures during pollination were 23 °C/10 °C. Flowers were hand pollinated with self- or cross-pollen at 2-day intervals ranging from 0 to 8 days after anthesis (DAA). Flower age at pollination had a significant effect on both fruit set and seed number per fruit. Rabbiteye blueberry flowers were able to produce optimum fruit set during a period of at least five days. Fruit set was markedly reduced 6 to 8 DAA, depending on the cultivar. Flower age at pollination also had a significant effect on stigmatic receptivity, which was assessed as the number of germinated tetrads on the stigma 24 hours after pollination. Stigmas pollinated 0 DAA had a significantly lower number of germinated tetrads than those pollinated 8 DAA. Flower age at pollination and stigmatic receptivity were positively associated. To our knowledge, this is the first quantitative evidence of delayed stigma maturation in blueberry. Stigmatic receptivity and fruit set were not correlated. Overall, the data strongly suggest that stigmatic receptivity was not a limiting factor for fruit set of `Brightwell' and `Tifblue'. It is hypothesized that ovule longevity determines the duration of flower receptivity in these two rabbiteye blueberry cultivars.

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Many bromeliad species indigenous to the rain forests of Central and South America are threatened because of over-collection and habitat destruction. Studies were conducted to develop propagation protocols for Tillandsia eizii, a rare ornamental bromeliad of ceremonial significance to the Highland Maya communities in Chiapas, Mexico. We anticipate using in vitro propagation for the conservation of this species with the potential of utilizing bromeliads as an alternative and sustainable forest resource. Protocols were developed for the sterilization and germination of axenic seed. Seedling growth in vitro was assessed and outplanting studies were conducted. Media were evaluated to promote adventitious bud production in experiments using the plant growth regulators naphthaleneacetic acid and benzylaminopurine. Pulse time and duration, as well as the stage of seed development, had a marked effect on bud production. The effects of various potting media on plant growth and survival were assessed. A pure pine bark medium elicited over 95 percent survival. Plants exhibited a “tank-like” morphology characteristic of plants in the wild.

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Tillandsia eizii is an epiphytic bromeliad that due to over-collection, habitat destruction, and physiological constraints has declined to near threatened status. This species exhibits high mortality in the wild, and seed are characterized by low percentages of germination. As a means to conserve this species, in vitro culture protocols were developed to enhance seed germination and seedling growth. A sterilization protocol using 70% ethanol for 2 minutes followed by 2.6% NaOCl for 40 minutes disinfested seed and promoted seedling growth. Sucrose incorporated into the culture medium had no effect on germination or growth, while NAA inhibited growth, but not germination. Cultures maintained under a 16-hour photoperiod at 22 °C exhibited greater growth than those grown at 30 °C. Seed that germinated in the dark remained etiolated and failed to develop even after transfer to light conditions. Plants grown in vitro were successfully acclimatized and transferred to the greenhouse. Over 86% survival and rapid growth were obtained with either an all-pine-bark medium, or a mixture of 2 redwood bark: 2 fir bark: 2 potting mix: 1 perlite. This demonstrated that in vitro culture of seed may be used to rapidly produce large numbers of T. eizii, and thus can be used for the conservation and reintroduction of this species.

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Changes in lipid and total protein content of somatic embryos of pecan (Carya illinoinensis) were estimated during maturation, cold treatment alone (3, 5, or 8 weeks) or cold followed by dessication (3, 5, or 7 days). Triglyceride was estimated colorimetrically and methyl esters of fatty acids were analyzed by GC-MS. Total protein was extracted from the same tissue with 2% SDS in Tris·HCL buffer. Triglyceride content of enlarged somatic embryos was significantly lower than zygotic embryos and further declined after 5 weeks cold treatment. An even greater decline was observed during the desiccation treatment. The most abundant fatty acids in small and enlarged somatic embryos are linolenic > palmitic > oleic > stearic acid. However, the molar ratio of linolenic to oleic reached 1:1 after 5 weeks of cold treatment. During enlargement, protein content increased to levels found in zygotic embryos, with desiccation resulting in further elevation.

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Tissue culture is a useful means to clonally propagate new ornamental plant selections, particularly when plant material is limited and/or conventional propagation methods are ineffective. An efficient in vitro multiplication protocol was established to propagate a new goatsbeard hybrid (Aruncus dioicus, × A. aethusifolia). The hybrid is of interest because it exhibits a dwarf habit, delicate white flower panicles and fern-like leaves, yet is tolerant to heat and humidity. Experiments were conducted to evaluate explant type (nodes, stems, leaves, and floral parts), disinfestation procedures, and media formulations including varying concentrations of 6-benzylaminopurine (BAP) and naphthalene acetic acid (NAA). Rapid plant regeneration was obtained with a shoot organogenesis system using a half strength Murashige and Skoog medium supplemented with 4.4 μmol BAP, 0.54 μmol NAA, 30 g·L-1 sucrose, and 3.0 g·L-1 GelGro. Studies compared the performance and yield of plants rooted using different in vitro and ex vitro methods. Ex vitro rooting of shoots during greenhouse acclimatization under mist was most effective. Regenerated plants exhibited uniform and rapid growth, and performed well in greenhouse and field evaluations.

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Georgia plume, Elliottia racemosa (Ericaceae), is a small tree endemic only to the state of Georgia, where it is listed as a threatened species. Information about genetic relatedness is critical for establishing approaches for safeguarding, reintroduction, and conservation of this rare species. The genetic relationships among and within selected georgia plume populations were evaluated using random amplified polymorphic DNA (RAPD) in conjunction with site visits at which time a census and GPS survey were conducted. Populations ranged from those containing eight to over 1000 individuals with most populations containing few plants (less than 50 individuals). With one exception, small populations with less than 50 individuals had more genetic similarity than populations with greater numbers of plants. Two protected populations containing large numbers of individuals were sampled extensively. Genetic similarity of individuals was not associated with plant proximity within a population. The small number of individuals and geographic isolation characteristic of many populations were associated with high within-population genetic similarity. Conservation priorities should be given to preserving as many different populations as possible to retain the genetic diversity of the species. Whether the narrow genetic variation found in some populations may be contributing to lack of sexual reproduction in the wild is an area for further study.

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