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Xinwang Wang, Robert N. Trigiano, Mark T. Windham, Renae DeVries, Timothy A. Rinehart, James M. Spiers and Brain Scheffler

The genus Cornus consists of many species, of which C. florida, C. kousa, C. mas, and C. stolonifera are four main ornamental species in North America, Asia, and Europe. For example, over 200 cultivars of C. florida alone have been developed for the nursery industry. Microsatellite loci, or SSR, are useful markers for studying genetic diversity and for creating linkage maps of the various species. The objective of this study was to investigate the genetic diversity between these four Cornus species and eight hybrids. Evaulation of the diversity will be useful in assessing the selection pressure of breeders and/or genetic drift of these dogwood cultivars/lines. Fifteen SSR primer pairs were selected to examine 56 Cornus cultivars and/or lines of the four species and hybrids. The study included 28 C. florida cultivars and lines, 15 C. kousa cultivars and lines, four C. stolonifera cultivars, one cultivar of C. mass and eight hybrids between various Cornus species. An exceptionally high level of diversity was detected among the 56 entries in both the number and size range of SSR alleles. A total of 95 alleles with an average of 7.8 alleles per loci were detected among these 56 genotypes. These selected Cornus cultivars and/or lines could be clustered into four to six subgroups. Some Cornus species were integrated into other species groups, suggesting gene flow between species via the breeding or evolution. SSR markers can contribute to the exploitation of genetic diversity for existing Cornus germplasm. For further study, examination of more SSR loci could explain more completely the diversity among these Cornus cultivars and lines.

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J. E. Staub and Jinsheng Liu

The genetic diversity among Cucumis sativus var. sativus (commercial cucumber) (1), var. anatolicus (2), var. cilicicus (3), var. europaeus (4), var. falcatus (5), var. indo-europaeus (6), var. irano-turanieus (7), var. izmir (8), var. sikkimensis (9), var. squamosus (10), var. testudaceus (11), var. tuberculatus (12), var. vulgatus (13), and var. hardwickii (14) were assessed using 7 morphological characteristics and 9 isozyme loci to determine their potential use for plant improvement. Results of morphological comparison below. Isozyme and morphological analysis did not result in similar dendrogram depictions. Varieties 13 and 3 might have potential in plant improvement based on yield performance.

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Claudia Cunha, Tana Hintz and Phillip Griffiths

DNA extractions from 77 snap bean and 2 dry bean cultivars were evaluated for molecular polymorphisms. In total, 100 10-mer oligonuceotide primers were evaluated, and 31 primers that amplified clear and repeatable polymorphisms among bean cultivars were selected. These primers amplified a total of 49 polymorphisms between the cultivars and were used to differentiate the cultivars and evaluate the genetic diversity between them. All cultivars were clustered according to genetic similarities using GenStat 5.0 software, and groupings of pod types were observed when cultivars were separated based on a dissimilarity index. The RAPD polymorphisms will be useful for cultivar determination, seed purity testing and estimation of genetic distances.

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James Nienhuis, Paul Skroch and Steve Beebe

Nuñas are a type of common bean (Phaseolus vulgaris) that possess the unusual characteristic of popping or expanding their cotyledonary tissue when heated. Numerous landraces of nuña beans were domesticated in the Andean region of South America (Peru, Bolivia, and Ecuador) and have been grown and consumed in this region since antiquity. The practical consideration in the domestication of nuñas in the high Andes was likely due to the greater energy efficiency in cooking toasted vs. boiled seeds.The Phaseolus germplasm bank at CIAT (Centro Internacional de Agricultura Tropical) has developed a core collection of Andean beans that includes numerous nuña landraces. Based on the wide range of phaseolin types observed among nuña landraces, it has been hypothesized that nuñas may represent a greater source of genetic diversity compared to other landraces and cultivars of common bean. Eighty nuña accessions and 120 nonpopping common bean accessions were randomly sampled from the CIAT Andean germplasm core collection. The 200 accessions were characterized for 140 mapped RAPD markers. The objectives of our research were to 1) understand the genetic structure of nuña bean accessions relative to other Andean common beans, and 2) to measure the genetic distance and genetic diversity between nuña and other Andean bean populations.

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Margaret R. Pooler

Many popular crapemyrtle (Lagerstroemia L.) cultivars grown in the United States are interspecific hybrids between L. indica L. and L. fauriei Koehne. The 22 hybrid cultivars released from the U.S. National Arboretum contain primarily genetic material from L. fauriei PI 237884. Examining the genetic diversity ofL. fauriei specimens in the U.S. is valuable because of the historical and economic significance of the species, the increasing interest it is receiving as a source of new cultivars, and its threatened status in the wild. Our objectives were to examine molecular genetic diversity among L. fauriei accessions using Randomly Amplified Polymorphic DNA (RAPD) and Amplified Fragment Length Polymorphisms (AFLP) markers. Our results indicate: 1) RAPD and AFLP markers are generally consistent in the genetic relationships that they suggest; 2) the L. fauriei germplasm we examined falls into at least three distinct clusters; and 3) the genetic base of cultivated Lagerstroemia could be broadened significantly by incorporating some of this more diverse L. fauriei germplasm into breeding programs.

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J. Nienhuis, P. Skroch, M. Sass, S. Beebe, J. Tohme and F. Pedraza

The number of Phaseolus vulgaris germplasm accessions numbers more than 30,000. While the large numbers of accessions increase the probability of preserving genetic variability they simultaneously limit the efficient and routine utilization of this resource. From the approximately 4000 P. vulgaris accessions in the C.I.A.T. whole collection that were collected in Mexico, a core collection of 400 accessions was developed based on variation for agronomic performance, ecological adaptation, and seed characteristics. Random samples of 90 accessions each were drawn from the core and whole collections and evaluated for 224 polymorphic RAPD bands. Based on analysis of the RAPD data there were no significant differences in genetic diversity between the two samples. The correlation of marker frequency for the two samples was 0.984 confirming that the two samples represent the same population.

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V. V. Meglic, T. F. Horejsi, J. E. Staub and J. D. McCreight

The genetic diversity of 400 U.S. melon germplasm plant introductions was assessed using 35 enzyme systems. Polymorphisms were observed at 24 putative loci (Ac, Acp1, Acp4, Ak2, Ak3. Ak4, Fdp1, Fdp2, Fdp4, Gpi, Idh, Mdh2, Mdh4, Mdh5, Mdhb, Mpi1, Mpi2, Pgd1, Pgd2, Pgm, Pep-g1, Pep-1a, Pep-pap, Skdh) representing 17 different enzymes. Sixteen loci demonstrated simple Mendelian inheritance. Multivariate analyses aided in reduction of data using 16 loci and linkage relationships were observed among the plant introductions. Two of 16 loci (Pgd1 and Acp1) segregated independently. Fourteen loci were assigned into three linkage groups (A-C): A Fdp1, Fdp2, Acp4, Skdh; B Mdh2, Mdh4, Mdh5, Mdh6, Pep-g1, Pgm; C Mpi2, Ac, Idh.

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Amnon Levi, Claude E. Thomas, M. Newman, O.U. K. Reddy, X. Zhang and Y. Xu

Wide phenotypic diversity exists among American heirloom cultivars of watermelon (Citrullus lanatus var. lanatus). However, in published studies, low or no polymorphism was revealed among those heirlooms using isozyme or randomly amplified polymorphic DNA (RAPD) markers. In this study, experiments with inter-simple sequence repeat (ISSR) [also known as simple sequence repeat-(SSR-) anchored primers] and amplified fragment-length polymorphism (AFLP) markers produced high polymorphisms among watermelon heirloom cultivars. ISSR (111) and AFLP (118) markers (229 total) identified 80.2% to 97.8% genetic similarity among heirloom cultivars. The phylogenetic relations based on ISSR and AFLP markers are highly consistent with the parental records available for some of the heirloom cultivars, providing confidence in the dendogram constructed for heirlooms based on similarity values. As compared with RAPD markers, ISSRs and AFLPs are highly effective in differentiating among watermelon cultivars or elite lines with limited genetic diversity.

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Maureen C. O'Leary and Thomas H. Boyle

Isozyme markers were used to identify cultivars and assess the genetic diversity within a germplasm collection of 49 Hatiora Britt. & Rose clones. The collection included accessions of Easter cactus [H. gaertneri (Regel) Barthlott, H. graeseri Barthlott ex D. Hunt, and H. rosea (Lagerheim) Barthlott] plus H. herminiae (Campos-Porto & Castellanos) Backeberg ex Barthlott and H. salcornioides (Haworth) Britton & Rose. Seven enzyme systems were analyzed: aspartate aminotransferase, glucose-6-phosphate isomerase, leucine aminopeptidase, malate dehydrogenase, phosphoglucomutase, shikimate dehydrogenase, and triosephosphate isomerase. Thirteen loci and 42 alleles were identified. Twenty-one clones (43%) displayed unique isozyme profiles, but the remaining 28 clones shared isozyme profiles with one to three other clones. Percent polymorphic loci, mean number of alleles per locus, and mean heterozygosity were 69, 3.23, and 0.30, respectively, for the entire collection. Isozymes also proved useful for verifying that some progeny were genuine F1 hybrids.

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Grey Horton and Jim Luby

This study of genetic diversity in a wild ancestor of the cultivated strawberry was undertaken to describe patterns of variation in nature, assess worth of existing germplasm collections, and identify promising locations for future collection. Previous work reported a similar study of octaploid strawberry ranging east to west across North America. This complementary study focused on variation from north to south in the Rocky Mountains. The morphological diversity of 16 populations of Fragaria virgininia were characterized for morphological and molecular traits. Two clones of each of 133 genotypes from these populations were grown in a common environment in a greenhouse. Eighteen morphological traits, such as leaf area, runner color, and days to flowering, were measured and analyzed with principal components and canonical discriminant analyses. Molecular diversity data were obtained using seven randomly amplified polymorphic DNA primers. Resulting population marker frequencies were also subjected the previously describe anlayses. Differences due to latitude, longitude, and altitude were observed. Implications of the results will be discussed.