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interspecific hybrid was extracted so that it can be used to select cross-breeding parents in subsequent breeding programs and to test the DUS of the hybrid variety. Materials and Methods Sample collection and measurement of vegetative
Cucurbita maxima and C. pepo are difficult to hybridize, and it was our objective to generate F1 hybrids between ornamental cultivars of the two species. C. maxima `Lakota' and C. pepo `Jack O'Lantern'; and `OZ'; were selected as parents. `Lakota' (L) is an heirloom, hubbard-type cultivar producing pear-shaped, red-orange fruit with dark green mottling, `Jack O'Lantern'; (J) is an open-pollinated Halloween-type pumpkin cultivar and `OZ' is a Halloween-type hybrid. Sixteen plants of each cultivar were greenhouse-grown in a CRB design during the period July-Sept. 2003. Interspecific crosses were made in both directions, with intraspecific crosses (J × O) and selfs (L) serving as controls. Fruits were harvested about 20 d after pollination. Embryos were excised under aseptic conditions and grown on either full strength Murashige and Skoog (MS) media with 6% sucrose (S6), full strength MS media with 6% maltose (M6), or half strength MS media with 3% sucrose (S3). Fruit set was generally greater in the intraspecific crosses (33%) and selfs (67%) than in the interspecific crosses (15 %), with the notable exception of the interspecific combination L × J (85% fruit set). Embryos of interspecific and control crosses were about 1.5mm and >1cm long, respectively. Hypocotyl and root growth 10 d after plating was better on S3 (3.2 and 1.7 cm) than on S6 (1.6 and 0.25 cm) or M6 (0.35 and 0 cm), and a greater number of functional hybrids were obtained from embryos grown on S3 (6 plants) than on S6 (2 plants) or M6 (2 plants). The interspecific plants were backcrossed to one of the parents and novel combinations of shape, color and variegation in hybrid fruit were observed.
Crapemyrtle (L. indica and L. indica × L. fauriei hybrids) is one of the most popular flowering landscape plants in the U.S. Although many cultivars have been developed through breeding efforts, little has been published on the reproductive biology of the genus. The objective of this study was to evaluate barriers to successful self-seed production in crapemyrtle. Self-compatibility was assessed by comparing pollen tube growth, fruit and seed production, and seed germination following controlled self- and cross-pollinations. Observations of pollen tube growth at intervals up to 24 hours after self- and cross-pollination indicated no barriers to self-fertilization acting at the stigmatic or stylar level in L. indica, L. fauriei or cultivars derived from inter-specific hybrids of these two species. Self-pollinations of `Catawba', `Whit IV', `Tonto' and `Tuscarora' had lower percent seed pod set and seed germination than did cross-pollinations of these cultivars. The number of seeds per pod was lower when `Catawba', `Whit IV' and `Tuscarora' were self-rather than cross-pollinated, but no difference between `Tonto' self- and cross-pollinations was observed. When decreased pod set is combined with much lower seed germination for self-pollinations, selfing of crapemyrtle is extremely unproductive when compared to cross-pollination. A late-acting self-incompatibility system or inbreeding depression is indicated for L. indica and inter-specific crosses with L. fauriei.
Reciprocal crosses, both intraspecific and interspecific, were made among five Chilean species of Nolana (Solanaceae), a genus native to western South America. With the exception of N. paradoxa, plants of all species used were grown from mericarps collected from wild populations. Self-pollinations were generally not successful, suggesting obligate allogamy. A total of 333 hybridizations were performed, of which 109 were intraspecific and 224 interspecific. Successful intraspecific hybridizations, as measured by formation of fruits, were produced for N. acuminata (83%), N. elegans (94%), N. paradoxa (82%), and N. rupicola (100%), however viable hybrids were only obtained for N. paradoxa. Interspecific combinations resulted in over 80% fruit set, however, viable hybrid success ranged from only 1% to 5%. Crosses included N. elegans × N. paradoxa with 20 viable hybrids, N. paradoxa × N. elegans with two hybrids, N. paradoxa × N. rupicola with seven hybrids, and N. rupicola × N. paradoxa with five hybrids. Exceptions included crosses involving N. aplocaryoides, with up to 20% fruit set. Also, the combination N. paradoxa × N. aplocaryoides with five hybrids, had a 26% success. All interspecific hybrids obtained had N. paradoxa as one of the parents, which could be related to artificial selection for high germination frequency.
Interspecific hybridization, pollen-stigma incompatibility, and DNA sequence analysis were used to study the relationships among hazelnut (Corylus) species. Interspecific crosses resulted in a wide range of cluster set from 0% to 65%. Reciprocal differences were common. In general, crosses involving C. avellana and C. heterophylla were more successful when used as pollen parents, but crosses involving C. americana were more successful when it was the female parent. C. cornuta, C. californica and C. sieboldiana intercrossed freely in both directions, as did C.colurna and C.chinensis. The Asian species, C. sieboldiana, C.heteropyhlla, and C. chinensis, were not cross-compatible with each other. Fluorescence microscopy showed that pollen-stigma incompatibility exists within and among wild hazelnut species, in addition to the cultivated European hazelnut C. avellana. Pollen-stigma incompatibility and embryo abortion (blank nuts) appear to be major blocks to interspecific gene flow. In addition, the chloroplast matK gene and the Internal Transcribed Spacer (ITS) region of the nuclear ribosomal DNA (nrDNA) were amplified and sequenced. The matK sequence was highly conserved and thus was not informative. However, the ITS sequence was highly informative and parsimony analysis agreed with morphological similarities. Corylus species were placed into four groups: 1) C. avellana, C. maxima, C. americana and C. heterophylla 2) C. colurna, C.chinensis, and C. jacquemontii 3) C. cornuta, C. californica and C. sieboldiana 4)C. ferox.
The species of section Batatas represent the primary potential source of wild germplasm for sweet potato breeding. Their wide distribution and adaptation make their use desirable, but their direct use is constrained by their ploidy level (2x, and 4x, in contrast with cultivated I. batatas which is 6x) and lack of storage root production.
We investigated 4x clones of interspecific origin (6x I. batatas 2x I. trifida) as bridges to introgress genes from several wild species of the section Batatas to I. batatas. Six 2x wild species from different origins were reciprocally crossed to the 4x clones. The crosses were successful only when the diploid wild species were used as females (2x × 4x) indicating unilateral interspecific incompatibility. The unsuccessful types of crosses (4x × 2x) were repeated using wild hybrid males containing I. trifida in their parentage. This time only those crosses involving a hybrid having I. trifida as its female parent produced seeds. Progenies from the successful 2x × 4x crosses were diploid instead of the expected triploid. Triploid progenies were obtained only in the 4x × (2x hybrid) crosses. Some triploid progenies produced 2n pollen in varying frequencies. These results show different levels of crossing barriers among Ipomoea species and give us alternative pathways for overcoming them. I. trifida was identified as a possible bridge species.
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.
Hydrangea popularity and use in the landscape has expanded rapidly in recent years with the addition of remontant varieties. Relatively little is known about the genetic background or combinability of these plants. We recently established microsatellite markers for hydrangea and evaluated their utility for estimating species diversity and identifying cultivars. We also verified an interspecific cross using these markers. Future research includes marker assisted breeding, particularly with respect to remontant flowering traits.
Isozyme inheritance and variation in Actinidia was investigated using 23 enzyme systems. Ten isozyme loci from six enzyme systems, Acp-2, Est, Prx-1, Prx-2, Prx-4, Prx-5, Pgi-2, Pgm-2, and Tpi, were found to be inherited as single Mendelian genes in families of two interspecific crosses. Disomic inheritance detected at ten loci in progenies of a cross between the hexaploid A. deliciosa × diploid A. chinensis, provided convincing evidence that A. deliciosa is an allohexaploid. Allelic segregation for tetrasomic inheritance at ten isozyme loci was demonstrated in the progenies of a cross between the tetraploid A. chinesis × diploid A. eriantha, a result suggesting the autotetraploid origin of the tetraploid A. chinensis which apparently originated from its diploid ancestor A. chinensis. A high level of isozyme variation and heterozygosity were observed in the 22 cultivars and 56 plants of 28 Actinidia taxa. Allozyme phenotype can be used effectively for cultivar identification.
142 ORAL SESSION (Abstr. 666-672) CROSS-COMMODITY BIOTECHNOLOGY II/RFLPs