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interspecific hybridization is the direction of the cross, as this may affect its rate of success, the number of seeds produced, as well as the dormancy of the seeds due to maternal effects ( Morgan et al., 2010 ). In this respect, using S. melongena as the

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successful, naturally occurring interspecific hybridization via pollinator activity ( Wyatt and Broyles, 1994 ). Asclepias is also unusual in that they have two independent ovaries and, if pollinia are inserted perfectly, all subsequent seed will share a

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Abstract

Interspecific hybridization is a technique commonly used by plant breeders to transfer genes from one species to another. Interspecific hybrids are usually obtained with greater difficulty than intraspecific hybrids because genetic barriers to hybridization usually increase with an increase in genetic unrelatedness (6, 11, 18, 41). Breeders resort to interspecific hybridization only when the characters are absent or inadequately expressed at the intraspecific level. Stone-fruit breeders have made much use of interspecific hybridization in the improvement of Prunus cultivars and rootstocks (3, 5, 6, 8, 12, 14, 15, 18, 19, 28, 34, 36, 37, 41, 42, 43) particularly in the subgenus Prunophora (plums), because plum species tend to intercross more freely than do members of other subgenera (41, 42). This paper will review the problems that have been encountered in making interspecific Prunus hybrids and the techniques that have been used to overcome them. In addition, techniques are presented that have been employed successfully with other interspecific hybridizations which may have application for Prunus.

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produced relatively few seed setting flowers, seeds per capsule, and number of germinated seeds. The results indicated that some interspecific cross-compatibility barriers prevented hybridization and obtaining normal seeds from crossing combinations

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lilies. To obtain desired traits of interest in cultivars, breeders have tried to make interspecific hybridizations. In the past, interspecific hybridizations in water lily have been performed for the hope of creating a blue hardy water lily hybrid, but

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An interspecific hybridization program involving ancestral species of the Begonia Semperflorens Cultorum Group was initiated to expand the genetic base of this group. Viable seeds were recovered from four reciprocal crosses. F, progenies were sterile and phenotypically intermediate between parental types. Fluorescence microscopy revealed evidence of both sporophytic and gametophytic incompatibility. Post-pollnation responses of flower petals were positively correlated with pollen tube growth in stigmatic, stylar, and ovarian tissue. A digital image analyzer was used to facilitate seed counts and to determine the percentage of ovules that developed into seeds. Seed germination percentages ranged from 0-91 for crosses to 80-99 for selfs.

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An interspecific hybridization program involving five species of Impatiens was initiated to delineate incompatibility barriers. With the exception of one cross, no viable hybrid seed was recovered. Fluorescence microscopy revealed foreign pollen tubes to reach ovules in all crosses, although not all ovules were approached. A histological study involving I. auricoma Baill. and I. walleriana Hook f. ensued to confirm the presence of hybrid embryos. Developing I. walleriana × I. auricoma and reciprocal hybrid embryos were compared to self embryos. Development of hybrid embryos was delayed as early as five days post-pollination. I. walleriana × I. auricoma embryos continued to develop for 8 days post-pollination, but did not reach a size greater than a 5-day self embryo. Excessive endosperm was observed in the hybrid. I. auricoma × I. walleriana embryos continued to enlarge up to ovary abortion but did not reach a size greater than a 7-day self embryo and little to no endosperm developed. Disintegration of ovules included disorganization and collapse of the endosperm, and vacuolization and loss of turgidity of the embryo.

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Interspecific hybridizations among members of the genus Hamamelis (the witchhazels) and Corylopsis were carried out in 1993, 1994, 1995, and 1996 at the U.S. National Arboretum. Specifically, crosses involving the native witchhazel (H. vernalis and H. virginiana) and the Asian taxa (H. mollis, H. japonica, and H. × intermedia) were attempted in order to combine the ornamental qualities of the Asian species with the adaptability and fall blooming characteristics of the native species. Additionally, C. platypetala, a hardy species with small inflorescences, was crossed with C. himalaica, which has large showy inflorescences but is less hardy. Approximately 50 seedlings resulting from these crosses have been analyzed using randomly amplified polymorphic DNA (RAPD) markers to verify interspecific hybridization. Based on these assays, we report the first incidence of controlled interspecific hybridization between the Asian and native witchhazel taxa.

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plant species are brought into close proximity for seed production or planting, interspecific hybridization can occur ( Ellstrand, 1992 ). Interspecific hybridization could lead to genetic contamination of native wildflower seed being produced. If

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Abstract

Interspecific hybridizations among 6 Carica species, including the edible papaya, produced 2 hybrids previously unreported: C. monoica Desf. × C. goudotiana (Tr. & PI.) Solms (A)R and C. parviflora (A. DC.) Solms. × C. goudotiana (A)R. Other crosses producing viable seeds were: C. monoica × C. cauliflora Jacq., its reciprocal; C. goudotiana (A, B) × C. monoica and C. cauliflora (A, B) × C. pennata Heilbron, Svensk.

Three reciprocal pollinations of the above crosses and 9 other pollinations produced fruits with under-developed seeds which were non-viable. Carica papaya L. (Line 26) pollinated with pollen of C. cauliflora (A), C. parviflora, C. monoica and C. goudotiana (A)R produced fruits with non-viable seeds. Three crosses, C. pennata × C. goutotiana (B), C, papaya (Line 5B) × C. pennata and C. goudotiana (A)R × C. cauliflora (A) produced parthenocarpic fruits (ovules completely undeveloped). Most cross pollinations which failed to set fruit were reciprocals of those which produced non-viable seed and parthenocarpic fruits. Differences in compatibility and seed viability were shown by lines of C. cauliflora from El Salvador and Venezuela and by C. goudotiana from Colombia and Venezuela.

Four interspecific hybrids are described. Heterosis was shown in 2 hybrids for tree height, trunk circumference, and number and wt of fruits.

Only C. cauliflora and its hybrids did not show the usual visible reaction to a virus with symptoms resembling papaya mosaic and distortion ringspot. As the trees progressed in age, many died of root rot (associated with Phytophthora palmivora Butl. and Pythium aphanidermatum (Edson) Fitz.). Symptoms of this disease were not apparent in plants of C. cauliflora or its hybrids with C. monoica, although the latter species has been observed to be highly susceptible.

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