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Sandra Reed

Japanesesnowbell(Styrax japonicus Sieb. & Zucc.) is an outstanding small ornamental tree that is underutilized in the United States. Many of the cultivars of this Asian native frequently suffer spring freeze damage, especially when grown in the areas of the country that routinely experience dramatic fluctuations in late winter and early spring temperatures. The objectives of this study were to determine if there was variability within S. japonicus for time of budbreak and if this variability could be used for selecting plants with reduced susceptibility to spring freeze damage. In 1998, 224 open-pollinated seedlings were planted in the field. Percent budbreak was evaluated weekly during a 6-week period in Spring 1999 and 2000. While weather conditions varied greatly between the 2 years, there was good consistency between mean budbreak ratings in 1999 and 2000. There was a 4-week difference between the earliest and latest plants to break dormancy. Based on the 1999 and 2000 data, 28 plants were selected and propagated. A replicated trial involving these selections and three cultivars was carried out in 2002, 2003, and 2004. All of the selections broke bud later and suffered less freeze damage than `Emerald Pagoda' and `Carillon', but many performed similarly to `Pink Chimes'. Variation in height, width, caliper, and canopy shape was observed among the selections. There is an opportunity to utilize the genetic variability in S. japonicus for developing cultivars with reduced susceptibility to spring freeze damage.

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Sandra Reed*

Flowering dogwood (Cornus florida) is a popular flowering tree that is a mainstay of the southeastern U.S. nursery industry. Because cultivars of this species are primarily propagated through budding onto seed-propagated rootstock, a reliable source of seeds is needed. Disease- and weather-related problems may sometimes result in a shortage of dogwood seed. The objective of this study was to develop a method of storing dogwood seed that would allow growers to save seed during years in which good flowering and seed set occur for use when insufficient seed is available. Open-pollinated seeds were collected in Fall 1999, dried to 6%, 10%, and 14% moisture, and stored at -20, 5, and 22 °C. After 1, 2 and 3 years of storage, seed was stratified for 3 months and then planted in the greenhouse. Percent germination was compared to that of a subsample of the seed lot that had been stratified and planted following collection in Fall 1999. After 1 year in storage, seed dried to 10% and 14% moisture and stored at 22 °C failed to germinate; germination of the other samples ranged from 55% to 97% of that of the control sample. After 2 or 3 years in storage, all seed stored at 22 °C and the seed dried to 14% moisture and stored at 5 °C failed to germinate. Germination of the remaining samples ranged from 76% to 97% of the control in year 2, and from 72% to 109% in year 3. After 3 years in storage, seed dried to 6% moisture and stored at 5 °C and seed dried to 10% moisture and stored at -20 °C had the highest germination percentage and best seedling vigor. Development of a seed storage method for dogwood will benefit both dogwood producers and germplasm preservation efforts.

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Sandra M. Reed

Japanese snowbell (Styrax japonicus Sieb. & Zucc.) is an outstanding small ornamental tree that is underused in the U.S. One of the reasons this Asian native is not more widely planted is that it is subject to spring freeze damage. The objectives of this study were to determine if there was variability within S. japonicus for time of budbreak and if this variability could be used for selecting plants better adapted to areas of the country that frequently experience late spring freezes. During Spring 1999 and 2000, budbreak was evaluated weekly in 224 open-pollinated seedlings. While weather conditions varied greatly between the 2 years, there was good consistency between 1999 and 2000 data. There was a 4-week difference between the earliest and latest plants to break dormancy. Based on the 1999 and 2000 data, 28 plants were selected and propagated. A replicated trial involving these selections and three cultivars was carried out in 2002, 2003 and 2004. All of the selections broke bud later and suffered less freeze damage than the cultivars `Emerald Pagoda' and `Carillon', but many performed similarly to `Pink Chimes'. Variation in height, width, caliper and canopy shape was observed among the selections. There is an opportunity to utilize the genetic variability in S. japonicus for developing cultivars with reduced susceptibility to spring freeze damage.

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Sandra M. Reed

The objectives of this study were to evaluate self-fertility and to determine the effectiveness of pollinations made over a 4-day period in Japanese snowbell, S. japonicum Sieb. & Zucc. Pollen germination and pollen tube growth were observed in stained styles following cross- and self-pollinations made from 1 day before to 2 days after anthesis. One month after pollination, fruit set averaged 40% in cross-pollinations and 14% in self-pollinations. Two months later, about one-third of the fruit resulting from cross-pollinations had aborted and only one fruit remained from the self-pollinations. This study demonstrated that stigmas of S. japonicum are receptive for at least 4 days and that flowers should be emasculated prior to making controlled cross-pollinations.

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Sandra M. Reed

The objectives of this study were to evaluate self-incompatibility in Hydrangea paniculata Sieb. and H. quercifolia Bartr. and to determine optimum time for pollination of these two species. Flowers from three genotypes of each species were collected 1, 2, 4, 8, 24, 48, and 72 hours after cross- and self-pollination, stained with aniline blue and observed using a fluorescence microscope. In both species, pollen germination was observed on stigmas of over half of the flowers collected 4 to 72 hours after cross- or self-pollination. Differences in pollen tube length between cross- and self-pollinated flowers were noted from 8 to 72 hours after pollination in H. paniculata and from 24 to 72 hours after pollination in H. quercifolia. By 72 hours after pollination, most self-pollen tubes had only penetrated the top third of the style but cross-pollen tubes had grown to the base of the style and entered 40% to 60% of the ovules. Stigmas of H. paniculata were receptive to pollen from anthesis to 5 days after anthesis, while stigmas of H. quercifolia were receptive from 1 to 5 days after anthesis. This study provides evidence of a gametophytic self-incompatibility system in H. paniculata and H. quercifolia. Occasional self-seed set previously observed in these species was theorized to have been due to pseudo-self compatibility.

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Sandra M. Reed

Breeding efforts in Clethra alnifolia L., an ornamental shrub native to the Eastern U.S., are hindered by a lack of information on the reproductive behavior of this species. The objective of this study was to evaluate self-compatibility, time of stigma receptivity, and the relationship between time of pollen shed and stigma receptivity in C. alnifolia. Stigma receptivity and changes in floral morphology were monitored over a 7-day period beginning at flower opening. Pollen germination and pollen tube growth in styles were examined following self- and cross-pollinations using fluorescence microscopy. Seed set and germination were compared following self- and cross-pollinations. Anthers began to dehisce in `Hummingbird' and `Ruby Spice' the day after flowers opened, but stigmas did not become fully receptive to pollen until 2 days later. An increase in the length of pistils was observed following flower opening. Maximum elongation of pistils occurred at approximately the same time stigmas became receptive and could be utilized as an indicator of receptivity. While self-pollen tubes appeared to grow slightly slower than cross-pollen tubes, there was no indication of a self-incompatibility system acting at the stigmatic or stylar level in C. alnifolia. Self-pollinations of `Hummingbird' and `Ruby Spice' produced fewer seeds than did cross-pollinations of these cultivars. Germination of all seed obtained from this study was too poor to allow a comparison of germination rates of the self- and cross-pollinated seed. However, because a few self-progeny were obtained, emasculation is recommended when making controlled pollinations. The presence of a late acting self-incompatibility system or early-acting inbreeding depression was proposed as being responsible for the lower seed set following self-pollination.

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Keri Jones and Sandra Reed

Hydrangea arborescens L., or smooth hydrangea, is a shrub native to the eastern United States that produces large corymbs of pure white flowers in early summer. Rated as hardy to USDA cold hardiness zone 4, it is one of the most cold-hardy members of the genus. Hydrangea involucrata Sieb. is an Asian species that produces lavender-blue flowers in midsummer. This species, which is not widely cultivated in the United States, is only rated as hardy to zone 6 to 7. The objective of this study was to hybridize H. arborescens and H. involucrata for the purpose of combining cold hardiness and flower color. Reciprocal crosses were made between H. involucrata and H. arborescens during Summer 2003. No seed were obtained when H. involucrata was used as the maternal parent. Approximately 500 seeds were collected from H. arborescen × H. involucrata hybridizations, 36 of which germinated. Several of these seedlings were extremely weak and died at a young age. The remaining eight plants have not flowered and all possess reduced growth rates. Hybridity was verified using RAPD markers and morphological comparisons of hybrids and parents.

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Sandra M. Reed

Clethra alnifolia L., a native deciduous shrub cultivated as an ornamental, was recently hybridized with C. pringlei S. Wats. The purpose of this hybridization was to combine the cold hardiness and adaptability of C. alnifolia with the ornamental foliage of C. pringlei. While most of the C. alnifolia × C. pringlei hybrids more closely resembled C. alnifolia than the paternal species, a `Hokie Pink' × C. pringlei hybrid (NA71586) with foliage that flushes red like C. pringlei was recovered. The objectives of this study were to analyze cytologically the F1 and produce a F2 population from NA71586. Chromosome counts from root tips cells indicated that NA71586 has 32 chromosomes. Since the chromosome number of C. alnifolia is 2n = 32 and that of C. pringlei was found to be 2n = 16, NA71586 appears to have developed following fertilization of a C. alnifolia egg with an unreduced male gamete from C. pringlei. Both `Hokie Pink' and C. pringlei exhibited primarily bivalent pairing in pollen mother cells (PMCs). Over half of the PMCs from NA71586 contained 16 bivalents, indicating substantial homology within the C. alnifolia genome. It was theorized that C. alnifolia is either an autotetraploid that exhibits bivalent pairing or a segmental allotetraploid produced from hybridization of species with similar genomes. More than 700 F2 progeny were obtained from self-pollination of NA71586. Although many of the F2 progeny resembled NA71586, variation in foliage color, size and shape was apparent in the population.

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Sandra M. Reed

Clethra alnifolia, which is commonly known as summersweet, is an attractive deciduous shrub that produces fragrant flower in mid-summer. Breeding efforts are hampered by a lack of information on the reproductive behavior of this native species. The objective of this study was to evaluate self-compatibility in C. alnifolia. Pollen germination and pollen tube growth in styles were examined following self- and cross-pollinations using fluorescence microscopy. Seed set and germination were compared following self- and cross-pollinations. While self-pollen tubes appeared to grow slightly slower than cross-pollen tubes, there was no indication of a self-incompatibility system acting at the stigmatic or stylar level in C. alnifolia. Self-pollinations of `Hummingbird' and `Ruby Spice' produced fewer seeds than did cross-pollinations of these cultivars. Germination of all seed obtained from this study was too poor to allow a comparison of germination rates of the self- and cross-pollinated seed. However, because a few self-progeny were obtained, emasculation is recommended when making controlled pollinations. The presence of a late-acting self-incompatibility system or early acting inbreeding depression was proposed as being responsible for the lower seed set following self-pollination.

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Sandra M. Reed

Little information is available on the reproductive behavior of Hydrangea macrophylla (Thunb. Ex J.A. Murr.) Ser. The objectives of this study were to investigate time of stigma receptivity, viability of pollen from sterile flowers, and self-incompatibility in this popular ornamental shrub. Pollen germination and pollen tube growth in styles were examined using fluorescence microscopy. Stigma receptivity was examined in cross-pollinations made from 1 day before anthesis to 8 days after anthesis. Maximum stigma receptivity for the two cultivars examined occurred from anthesis to 4 days after anthesis. Viability of pollen from sterile flowers was evaluated through pollen staining and observations of pollen tube growth. No significant difference in percent stainable pollen between fertile and sterile flowers was observed in any of the six taxa examined. Pollen germination and pollen tube growth were studied in cross-pollinations made using pollen from fertile and sterile flowers of two cultivars. For both cultivars, pollen tubes from fertile and sterile flowers grew to the same length and had entered ovules by 72 hours after pollination. Self-incompatibility was evaluated by comparing pollen germination and pollen tube growth in cross- and self-pollinations. In the five taxa examined, self pollen tubes were significantly shorter than cross pollen tubes in flowers that were examined 72 hours after pollination. This finding indicates the presence of a gametophytic self-incompatibility system in H. macrophylla.