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  • Author or Editor: Desmond R. Layne x
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Growth chambers constructed of photoselective plastic films were used to investigate light quality effects on flowering and stem elongation of six flowering plant species under strongly inductive and weakly inductive photoperiods. Three films were used: a clear control film, a far red (FR) light absorbing (AFR) film and a red (R) light absorbing (AR) film. The AFR and AR films intercepted FR (700 to 800 nm) and R (600 to 700 nm) wavelengths with maximum interception at 730 and 690 nm, respectively. The phytochrome photoequilibrium estimates of transmitted light for the control, AFR, and AR films were 0.71, 0.77, and 0.67. The broad band R:FR ratios were 1.05, 1.51, and 0.77, respectively. The photosynthetic photon flux was adjusted with neutral density filters to provide similar light transmission among chambers. Zinnia elegans Jacq., Dendranthema×grandiflorum Kitam. (chrysanthemum), Cosmos bipinnatus Cav., and Petunia×hybrida Vilm.-Andr. plants grown under the AFR film were shorter than control plants. The AFR film had no effect on height of Antirrhinum majus L. (snapdragon) or Rosa×hybrida (miniature rose). Anthesis of zinnia, chrysanthemum, cosmos (short-day plants), and miniature rose (day-neutral plant) was not influenced by the AFR films. Anthesis of petunia and snapdragon (long-day plants) was delayed up to 13 days by AFR films under weakly inductive photoperiods. In petunia, initiation and development of floral structures were not affected by the AFR films during strongly inductive photoperiods. However, during weakly inductive photoperiods, initiation of the floral primordia was significantly delayed and overall development of the floral meristem was slower than control plants indicating that the AFR films could increase the production time if long-day plants were produced off-season. Daylength extension with electric light sources could overcome this delay in anthesis yet achieve the benefit of AFR films for height reduction without the use of chemical growth regulators.

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Phylogenetic relationships within the Actinidia were investigated using randomly amplified polymorphic DNA (RAPD) markers. DNAs from 40 taxa, including 31 species encompassing all four sections and four series of the traditional subdivisions within the genus, were amplified using 22 preselected 10-mer oligonucleotide primers. A total 204 DNA bands were scored across the 40 taxa, of which 188 (92%) were polymorphic. A wide range of genetic similarity was observed among the taxa (0.13 to 0.61). The average similarity between varieties of the same species was 0.54, and between different species was 0.28, respectively. Although the phylogenetic analysis revealed a clear indication that section Leiocarpae was a monophyletic group, subdivisions of the other three traditional sections were poorly supported. The UPGMA phenogram showed that the majority of the species clustered into geographic subgroups in accordance with their natural distribution (the Yangtzi River, southeastern China, southern China and southwestern China). The intrageneric subdivisions of Actinidia appeared to be difficult, but some subdivisions could be explained by the geographic distribution of the species, particularly for species of Liang's sections of Maculatae and Stellatae. The phylogenetic relationships among several species with previous taxonomic uncertainty are also discussed on the basis of the RAPD data. The results of this study supplement our previous understanding of the Actinidia taxonomy based solely on morphological characters.

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The pawpaw [Asimina triloba (L.) Dunal] has great potential as a new fruit crop. A pawpaw variety trial was established in Fall 1995 in Princeton, Ky. as a joint Kentucky State Univ.-Univ. of Kentucky research effort with the objective to identify superior varieties for Kentucky. A randomized block experimental design was used with 8 replicates of 28 grafted scion selections on seedling rootstock. Cultivars being tested included Middletown, Mitchell, NC-1, Overleese, PA-Golden, Rappahannock, Shenandoah, Sunflower, Susquehanna, Taylor, Tay-two, Wells, and Wilson. The other 15 clones were selections from the PawPaw Foundation. In 2002 and 2003, the following parameters were examined: tree survival, trunk cross-sectional area (TCSA), average fruit weight, total fruit harvested per tree, average fruit per cluster, total yield per tree, and yield efficiency. In 2003, 54% of the trees had survived, with `Susquehanna' (13%) showing the poorest survival. Based on TCSA, most selections displayed excellent vigor, with the exception of the selections: 5-5 and `Overleese'. Average fruit weight was greatest in 1-7-2 (194 g), 1-68 (167g), 4-2 (321 g), 5-5 (225 g), 7-90 (166g), 9-58 (176 g), 10-35 (167 g), NC-1 (180 g), `Sunflower' (204 g), and `Shenandoah' (168g), with the smallest fruit in `Middletown' (70 g), `Wells' (78 g), and `Wilson' (88 g). The selections `Wilson' (81), `Middletown' (75), and `Wells' (70) had the greatest average number of fruit per tree, whereas 4-2 (9), 5-5 (17) and 8-20 (15) the fewest. Yield efficiency and average fruit per cluster also varied greatly among selections. Several pawpaw selections in the trial show promise for production in Kentucky.

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Pawpaw (Asimina triloba) is an under-exploited small tree with commercial potential as a fruit crop, ornamental tree, and source of secondary products with insecticidal and medicinal properties. It is most often propagated from seeds that are recalcitrant and must be stored moist at a chilling temperature. Seeds display combinational (morphophysiological) dormancy. Endogenous, physiological dormancy is broken by about 100 days of chilling stratification followed by a period of warm moist conditions where the small embryo develops prior to seedling emergence about 45 days after the warm period begins. Pawpaw cultivars with superior fruit characteristics are propagated by grafting onto seedling understocks. The most common practice is chip budding. Other methods of clonal propagation have proven problematic. Pawpaw can be propagated from cuttings, but only in very young seedling stock plants. Micropropagation from mature sources is not yet possible, but shoot proliferation has been accomplished from seedling explants and explants rejuvenated by induction of shoots from root cuttings of mature plants. However, rooting of microcuttings and subsequent acclimatization has not been successful.

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The pawpaw [Asimina triloba (L.) Dunal.] is a tree fruit native to many areas of the southeastern and mid-western United States. Kentucky State University (KSU) is designated as a satellite repository for Asimina for the U.S. Department of Agriculture (USDA), National Plant Germplasm System (NPGS). An assessment of the level of genetic diversity in cultivated pawpaw would assist in development of the future germplasm repository collection strategies for cultivar improvement. The objectives of this study were to identify intersimple sequence repeat (ISSR) markers that segregate in a simple Mendelian fashion and to use these markers to assess genetic diversity in 19 pawpaw cultivars. Leaf samples from the 34 progeny of controlled crosses (1-7-1 × 2-54 and reciprocal) and the parents were collected, DNA was extracted, and subjected to the ISSR methodology using the University of British Columbia microsatellite primer set #9. Seven primers yielded 11 Mendelian markers with either a 3:1 or 1:1 ratio that was confirmed by chi-square analysis. Analysis of genetic diversity using 10 of the ISSR markers from 19 pawpaw cultivars revealed a moderate to high level of genetic diversity, with a percent polymorphic loci P = 80 and an expected heterozygosity He = 0.358. These diversity values are higher than those reported for cultivated pawpaw using isozyme or randomly amplified polymorphic DNA (RAPD) markers, indicating that the ISSR marker methodolgy has a higher level of discrimination in evaluating genetic diversity in pawpaw and/or pawpaw has greater levels of genetic diversity than previously found.

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