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Bruce L. Dunn and Jon T. Lindstrom

into B . davidii would be difficult. Similar sterility problems were also reported in F1 progeny after intersectional hybridization of diploids B . madagascarensis × B . asiatica Lour. ( Tobutt and Prevette, 1993 ). Not all intersectional

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Agnes RICROCH, Robert J. BAKER, and Ellen B. PEFFLEY

Biotin- and fluorescein-labeled probe has been used to map. specific sunflower rDNA sequences by in situ hybridization on mitotic chromosomes of Allium cepa, Allium fistulosum and interspecific hybrid derivatives, There are three hybridization sites in A. cepa and more than six in an interspecific triploid. This in situ hybridization technique offers new cytogenetic markers useful in the construction of a physical genomic map of Allium and offer a means to document introgression of these genomes.

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Xuejuan Chen, Ming Sun, Jianguo Liang, Hui Xue, and Qixiang Zhang

) started to breed new garden chrysanthemums in 1961, hybridizing dwarf cultivars with wild species through mixed pollination or open pollination. After generations of hybridization and selection, groundcover chrysanthemums were developed, and many

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Yi-Xuan Kou, Hui-Ying Shang, Kang-Shan Mao, Zhong-Hu Li, Keith Rushforth, and Robert P. Adams

cypress, yellow cypress, alaska yellow cypress, alaska cedar, nootka cedar, yellow cedar, and alaska yellow cedar) ( Farjon, 2005 ; Mitchell, 1996 ; Owens et al., 1964 ). Leyland cypresses were first raised through spontaneous hybridization in the United

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Anfu Hou and Ellen B. Peffley

Introgression of genes in species crosses can be observed morphologically in backcrossed or selfed progenies, but the phenotype does not give information about the movement of DNAs. Cytogenetic markers allow for visualization of specific DNAs in a genome. Few cytogenetic markers are available in onion to monitor the introgression of DNA in species crosses. Genomic in situ hybridization (GISH) provides a way to locate unique DNA sequences contributed by parents. We are using GISH to monitor the movement of DNAs from A. fistulosum into A. cepa. Results of experiments using A. fistulosum as probe DNA, and A. cepa as blocking DNA will be reported. Also presented are hybridization sites observed in F1BC3 progeny of the GISH.

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Margaret R. Pooler, Ruth L. Dix, and Joan Feely

The issue of invasive plants has become a concern to a variety of groups, including environmentalists, policymakers, and nurserymen. Although many surveys of invasive plants have been made, little research on the biology of hybridization has been conducted. Bittersweet (Celastrus) species serve as a good model system to test the effects of interspecific hybridizations since native and introduced species are found in the U.S. The American bittersweet (Celastrus scandens L.) is a deciduous climbing or twining shrub native to eastern and central North America. Although the bark has been used for medicinal purposes, the plant is cultivated as a nursery crop primarily for its bright red berries. In its natural habitat, native bittersweet is also an important source of food and cover for wildlife. Over the past several decades, populations of native bittersweet have declined to such low levels that some states are considering listing it as a threatened species. One reason for the rarity of American bittersweet in the wild is thought to be competition and possibly hybridization with an aggressive introduced species, oriental bittersweet (Celastrus orbiculatus Thunb.), which was introduced from Asia into the U.S. in 1860 as an ornamental. This plant can form dense, tangled, impenetrable thickets or climb small trees to girdle and smother them. It has been seen in at least 21 states since it was first recorded as an escape plant in 1912. Our objective was to determine whether oriental bittersweet can hybridize with native bittersweet, thus contributing to the loss of native populations in the United States. We performed controlled pollinations using C. scandens as the female parent and C. scandens or C. orbiculatus as the male parent. Although the intraspecific pollinations resulted in significantly more germinating seedlings than the interspecific crosses, the seedlings from the interspecific crosses had less seed dormancy and were more vigorous and more quick to vine than the intraspecific seedlings. These results indicate that the decline of the American bittersweet may be due to interspecific hybridizations with the invasive introduced species.

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Jude Grosser, Milicia Calovic, Patricia Serrano, Fred Gmitter Jr., and J. L. Chandler

The international fresh citrus market now demands high-quality, seedless fruit that must also be easy to peel for consumer convenience, especially when considering new mandarin varieties. High quality varieties that historically perform well in Florida are generally seedy. Florida is therefore losing market-share to `Clementine' and other seedless varieties produced in Mediterranean climates, including Spain, Morocco, and California. In our ongoing program, somatic hybridization and cybridization via protoplast fusion are now playing a key role in strategies to develop competitive seedless mandarin hybrids adapted to Florida. Somatic hybridization is being used to combine elite diploid parents to produce high quality allotetraploid breeding parents that can be used in interploid crosses to generate seedless triploids. Several thousand triploid mandarin hybrids have been produced under the direction of F.G. Gmitter, Jr. Some of our allotetraploid somatic hybrids are producing fruit with direct cultivar potential, i.e., 'Valencia' sweet orange + `Murcott' tangor. New somatic hybrids produced in our program will be discussed, including `Page' tangor + `Dancy' mandarin, `Page' tangor + `Kinnow' mandarin, and `Hamlin' sweet orange + LB8-9 tangelo. Somatic cybridization is being used to transfer CMS (cytoplasmic male sterility) from the seedless `Satsuma' mandarin to other seedy varieties via mtDNA transfer, in efforts to make them seedless. New somatic cybrids produced in our program that contain the `Satsuma' CMS include `Murcott' tangor and `Kinnow' mandarin. Details of these results and other progress will be discussed.

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R.H. Bors and J.A. Sullivan

The potential of using Fragaria vesca L. as a bridge species for interspecific hybridization to F. nilgerrensis Schlect, F. nubicola Lindl., F. pentaphylla Losinsk, and F. viridis Duch. was investigated using a wide germplasm base of 40 F. vesca accessions. This study was successful in producing many hybrids between F. vesca and other diploid species indicating its value as a bridge species. Of the species used as males, F. nubicola, F. pentaphylla, and F. viridis accessions were more successful, averaging 8 to 16 fruit and 16 to 25 seeds/fruit. It was most difficult to obtain hybrids with F. nilgerrensis, which had only three seeds per fruit. Differences among pollen donors were minimal when hybrid seeds were germinated in vitro. For different species combinations, 75% to 99% of seeds had embryos and 77% to 89% of these embryos germinated. The lack of significant differences in crossability variables among the four F. vesca subspecies [i.e., ssp. americana (Porter) Staudt, ssp. bracteata (Heller) Staudt, ssp. vesca L., and ssp. vesca var. semper-florens L.] demonstrated the similarity between these species and the strong potential for gene flow between F. vesca and other diploid species. As European and North American F. vesca subspecies are not sufficiently divergent to differ in interspecific hybridization, F. vesca may be a younger species rather than an older progenitor species.

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Yasumasa Takatsu, Masakazu Kasumi, Toru Manabe, Mikio Hayashi, Eiichi Inoue, Wataru Marubashi, and Masaru Niwa

Interspecific hybridization between a modern cultivar of Gladiolu×grandiflora hort. (2n = 60) and the wild species G. tristis L. (2n = 30) was made to introduce characteristics of the wild species into the cultivated one. Gladiolus ×grandiflora is a summer-flowering species, and G. tristis flowers in winter. The effect of storage temperature on pollen viability was tested, as long-term storage of pollen was necessary to facilitate crossing these two species. Pollen of G. tristis could be stored at -20 °C for ≈1 year, and was more practical than storage at -80 °C. Air temperature affected pollen tube growth, fertility, and fruit set in the cross between G. ×grandiflora and G. tristis, and low temperatures (15 to 20 °C) were best. The morphological data and flow cytometric analysis showed that the F1 plants were hybrids between G. ×grandiflora and G. tristis.

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K. Heuss-La Rosa, R. Hammond, J.M. Crosslin, C. Hazel, and F. Hammerschlag

In vitro micrografting was tested as a technique for inoculating peach [Prunus persica (L.) Batsch] with prunus necrotic ringspot virus (PNRSV). Cultured `Suncrest' shoots derived from a naturally infected tree (as indicated by ELISA testing) maintained virus in vitro, with virus concentrations in growing tips and folded leaves being several times those of fully expanded leaves. The infected shoots served as graft bases and the source of virus. Grafted tips were derived from `Suncrest' trees that had tested negative for the virus. Leaf samples were collected from the tips following grafting and analyzed for the presence of virus by slot-blot hybridization with a digoxigenin-labeled cRNA probed derived from PNRSV RNA 3. Rates of successful grafting were 55% and 73% in three trials and PNRSV was found in all tips analyzed. Virus concentrations approximated those found in the source shoots, suggesting that this method should be useful for screening transformed peach shoots for coat protein-mediated resistance to PNRSV.