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Abstract
Large scale commercial cultivation of blueberries and the breeding of improved cultivars both began after 1900 (33). Interspecific hybridization has been important in the development of commercial cultivars, and many combinations of species have been crossed in the course of taxonomic studies and in cultivar breeding. Nonetheless, the experimental study of blueberry interspecific hybridization is still in its infancy.
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.
require continuous moisture in the top meter of soil. Several intersectional crosses have produced hybrids in Vaccinium ( Ballington, 1980 , 2001 ; Darrow and Camp, 1945 ; Rousi, 1963 ) but our attempts to cross diploid V. arboreum with tetraploid
The hardy Actinidia species represent a source of genetic diversity for improving A. deliciosa (kiwifruit) as well as for creating new economically important cultivars through intra- and interspecific crosses. Attempts at breeding in Actinidia have been complicated by the existence of intraspecific as well as interspecific variation in ploidy. The haploid chromosome number in Actinidia is 29 and diploid (2n=2x=58), tetraploid (2n=4x=116), and hexaploid (2n=6x=174) levels have been identified. Because of the problems encountered when crossing parents differing in ploidy level, it is desirable to know the ploidy levels of plants to be used in breeding. We determined the ploidy levels of 61 Actinidia accessions currently available in the U.S., including primarily accessions of relatively winter-hardy species. The 61 accessions, representing eight species and three interspecific hybrids, were screened for ploidy using flow cytometry. Mitotic root tip cells from one plant from each putative ploidy level were examined microscopically to confirm the ploidy level derived from flow cytometry. There were 17 diploids, 40 tetraploids, and 4 hexaploids. Intraspecific variation was not found among accessions of the species arguta, callosa, deliciosa, kolomikta, melanandra, polygama, or purpurea. All kolomikta and polygama accessions were diploid. All arguta, callosa, melanandra, and purpurea accessions were tetraploid. Actinidia deliciosa was hexaploid. One chinensis accession was tetraploid. Two accessions (NGPR 0021.14 and 0021.3), acquired as chinensis, were hexaploid and may, in fact, be A. deliciosa based on their morphology. `Issai' (arguta × polygama) was hexaploid and `Ken's Red' and `Red Princess' (both melanandra × arguta) were tetraploid.
Interspecific hybrids of Exacum species (Gentianaceae) endemic to Sri Lanka possess excellent qualities for domestication as a new floriculture crop. The exact mode of floral induction and development responses are unknown, impeding the introduction of this potential crop. The interspecific hybrids evaluated are the result of controlled cross pollinations of E. macranthum. Arn. ex Griseb., E. trinervium (L.) Druce ssp. trinervium, and E. trinervium ssp. ritigalensis. (Willis) Cramer. The hybrids exhibit great genetic variability for horticultural traits. In addition, two growth and flowering patterns exist within the Penn State germplasm. Continuous-flowering genotypes flower throughout the year but more profusely and rapidly under late spring and summer conditions. In contrast, periodic-flowering genotypes exhibit two distinct seasonal habits. Under winter conditions, these accessions have a rosetted habit, much secondary branching, and few or no flowers. In summer conditions, they break their apical dominance, bolt, and produce flowers. As members of the Gentianaceae, Exacum hybrids produce an elegant blue flower with a striking yellow eye and bottle-shaped anthers. We evaluated the growth and flowering responses of Exacum interspecific hybrid accessions to photoperiod and irradiance. Accessions were evaluated under greenhouse conditions for floral production, rate of floral development, and growth characteristics. For the 20 accessions evaluated, supplemental irradiance under winter conditions resulted in greater floral production and much greater shoot and root mass accumulation. Little height and branching response occurred with supplemental irradiance. Of the 15 accessions evaluated under four photoperiod regimes, flowering and growth responses to photoperiod occurred under summer conditions but not in winter. An interaction among season, accession, and photoperiod revealed the complexity of Exacum germplasm and environmental responses.
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.
A set of 216 PCR-based molecular markers was screened for polymorphisms using two morphologically dissimilar broccoli lines, `VI-158' and `BNC'. Fifty-nine of these markers, representing 69 detected polymorphisms and two morphological markers, were used to construct a genetic linkage map of broccoli [Brassicaoleracea (L.) var. italica] from a population of 162 F2:3 families generated from the cross between these two lines. Ten genetic linkage groups were generated that spanned a distance of 468 cM with an average interval width of 9.4 cm. This map represents the first combined SSR and SRAP map of Brassica oleracea. Comparisons are made to existing maps of Brassicanapus and to inter-specific maps of Brassicaoleracea. To our knowledge this is the first linkage map of broccoli [Brassicaoleracea (L.) var. italica] and should provide a useful tool for the genetic analysis of traits specific to the italica subspecies.
Illinois, and Purdue University were used in this study. The cultivars and selections represented a diverse genetic background with pure Pyrus communis as well as interspecific hybrids with P. ussuriensis and P. pyrifolia . There were five P. communis
Forty eight cultivars and seedlings of plum involving the species Prunus americana, P. auqustifolia, P. cerasifiera, P. munsoniana, P. salicina, P. simoni, and P. triflora were evaluated for the presence of xylem limiting bacteria (Xyllela fastidiosa) and tree longevity. Plum leaf scald (PLS) ratings, based on the percent of scalded leaves in the tree were correlated with the concentrations of bacteria in the twigs and leaf petioles. Observations of symptoms of PLS and monitoring of progeny from interspecific crosses, cultivars, and seedlings indicate that resistance to the PLS organism is present in the Auburn material and heritable. Uniform infection of seedlings was made by double budding of one year whips with buds from infected trees. Resistance to PLS has been incorporated into horticultural types and seedlings are currently being evaluated for possible release for commercial and home use.
A genetic linkage map for blueberry has been constructed from over 60 RAPD (random amplified polymorphic DNA) markers that segregated 1:1 in a testcross population of about 40 plants. Prior to map construction, polymerase chain reaction conditions were optimized and RAPD marker reliability was confirmed. The mapping population was derived from a cross between diploid blueberry plants: Fl interspecific hybrid, `US388' (V. darrowi, `Fla4B' × V. elliottii, `Knight'), and another V. darrowi, `US799'. The map currently comprises 12 linkage groups corresponding to the basic blueberry chromosome number and covers a total genetic distance of over 800 cM, with a range of 2-30 cM between adjacent markers. Interestingly, a few pairs of marker loci behaved differently from both linked and unlinked loci, being found at a much higher frequency in the recombinant configuration than the parental configuration possibly suggesting selection for certain combinations of alleles.