Total DNA Content and Ploidy Levels in Linnaeoideae with a Focus on Abelia

The Linnaeoideae subfamily was created in Caprifoliaceae to represent the close relationship among the monophyletic genera Abelia, Diabelia, Dipelta, Kolkwitzia, Linnaea, and Vesalea. These closely related genera could possibly be a new source of ornamental traits for Abelia, an economically important genus of woody ornamental shrubs. Breeding among these genera could be challenging as only a few genera and species have a reported total DNA content, ploidy level, and chromosome number. The objective of this research was to fill that gap in the literature. We determined the total DNA content and DNA ploidy levels and estimated chromosome numbers of the species Abelia chinensis (two genotypes), Abelia macrotera var. engleriana, Abelia ×grandiflora, Abelia schumanii, Diabelia serrata, Vesalea floribunda, Zabelia tyaihyonii var. mosanensis, and the Abelia cultivars Edward Goucher, Francis Mason, Lavender Mist, Raspberry Profusion, and Rosy Charm® by flow cytometry. Raphanus sativus ‘Saxa’ was used as an internal standard for holoploid 2C total genome size estimation. For DNA ploidy and chromosome number, A. ×grandiflora (2n = 2x = 32) and Z. tyaihyonii var. mosanensis (2n = 36) were used as internal standards. We also measured the pollen size and stomata length of the species A. chinensis (two genotypes), A. macrotera var. engleriana, V. floribunda, A. ×grandiflora, A. schumanii, and D. serrata, and the Abelia cultivars Francis Mason and Raspberry Profusion. All genotypes have a 2C holoploid total DNA content between 0.87 and 0.95 pg DNA (∼850–930 Mb), except for V. floribunda and Z. tyaihyonii var. mosanensis, which have 1.94 and 1.91 pg DNA, respectively (∼1880 Mb). All genotypes are diploid with 2n = 2x = 32, except for V. floribunda and Z. tyaihyonii var. mosanensis, which have 36 chromosomes (2n = ?x = 36). We observed significant variability in stomata sizes and pollen diameter independent of and not correlated with genome size or chromosome number. A. ×grandiflora has a high percentage of dead pollen (∼30%), as does V. floribunda (43%). This high percentage of dead pollen in the natural species V. floribunda could be the result of aneuploidy. This is the first report of total DNA content in A. chinensis, D. serrata, and Z. tyaihyonii var. mosanensis; total DNA content and estimated chromosome number in V. floribunda; total DNA content and DNA ploidy levels in A. ×grandiflora, A. macrotera var. engleriana, and A. schumanii; and total DNA content, estimated chromosome number, and DNA ploidy levels in the Abelia cultivars Edward Goucher, Francis Mason, Lavender Mist, Raspberry Profusion, and Rosy Charm®

Effect of Pericarp Removal, Gibberellic Acid Treatment, and Stratification on Seed Germination of Abelia ×grandiflora

Abstract Seed germination within Abelia R. Br. spp. has been described as slow and inconsistent. An experiment was conducted with seeds of Abelia ×grandiflom (André) Rehd. (glossy abelia) to test procedures to increase germination percentage, uniformity and rate. The effect of pericarp removal was examined on seeds with no additional treatment, and on seeds that were stratified (moist-prechilled) for 60 days at 4C (39F) or immersed in 100 mg/liter gibberellic acid for 24 hr. Treatments were replicated five times with 15 seeds per replication. Seeds were sown on sphagnum peat, and germinated under mist in a greenhouse. Weekly germination counts were recorded for 8 weeks. Seeds with intact pericarps germinated at a significantly higher percentage than those without pericarps. Stratified seeds germinated in fewer days than the other treatments. The combination of stratified seeds with intact pericarps gave the best overall response, with final germination of 62% and a reduction in germination time to 14 days (to reach 90% final germination) as compared to 35 days for untreated seeds.</jats:p

Attractiveness of Species of Vitex (Chastetree) to Pollinators

Abstract Native and non-native bees are important pollinators of both food and ornamental crops. However, bee populations across the world have declined, mainly through loss of habitat. Careful selection of landscape plants in urban areas can help mitigate habitat loss and create new habitat for pollinators. Ten mature genotypes of Vitex, comprising V. agnus-castus L., V. negundo L., and a hybrid between V. agnus-castus x V. rotundifolia L. f., were evaluated during June and July 2016 to assess their attractiveness to pollinators. Pollinator counts were taken two times daily, at 9:00 a.m. and 11:00 a.m., twice weekly for three weeks. Pollinators were also captured from the Vitex plants for identification. Insects captured from Vitex plants were identified to genus and bumblebees [Bombus spp. (Latreille, 1802)] were further identified to species. Bumblebees and honeybees [Apis mellifera (Linnaeus, 1758)] were more numerous on Vitex plants than carpenter bees. V. agnus-castus plants attracted more bumblebees than honeybees. V. negundo and the V. agnus-castus x V. rotundifolia hybrid attracted more pollinators over the course of the study than V. agnus-castus. Our study shows that Vitex plants can be a good resource to support pollinators in an urban landscape. Index words: urban landscape, bumblebees, honeybees; Vitex agnus-castus, Vitex negundo, Vitex rotundifolia. Species used in study: Vitex agnus-castus L.; Vitex negundo L.; Vitex rotundifolia L.</jats:p

Evaluation of Deciduous Azaleas for Cold Hardiness Potential in the Southeastern United States

Abstract Twelve taxa of deciduous azalea were evaluated using laboratory procedures to determine hardiness of stems and flower buds. Rhododendron atlanticum, ‘My Mary’, ‘Nacoochee’, and ‘TNLV1’ exhibited the greatest stem cold hardiness, surviving to at least −29C ± 1 (−20F ± 2) in February 1996. Rhododendron oblongifolium exhibited the least stem cold hardiness, surviving to only −11C ± 1 (10F ± 2). All results were consistent with previous field studies. Except for R. viscosum and R. serrulatum, lowest survival temperatures for stems were analogous to reports available in the literature. Rhododendron viscosum and ‘My Mary’ had the lowest survival temperature recorded for flower buds, −23C ± 1 (−9F ± 2), in February 1998 and February 1999, respectively, though not significantly different than most other taxa examined. Lowest survival temperatures for flower buds varied from published accounts, with buds in the present study being less hardy than previously reported. Differences from published reports in the lowest survival temperatures of stems and flower buds are attributed to provenance, temperature fluctuations, cultural effects on the plants, and differences among freeze test protocols.</jats:p

Stem and Leaf Hardiness of 12 Abelia Taxa

Abstract Twelve taxa of Abelia were evaluated using laboratory procedures to determine maximum stem and leaf hardiness and to evaluate timing of acclimation and deacclimation over a two-year period. Among the 12 Abelia taxa evaluated, ‘John Creech’ was among the hardiest taxa for both stems and leaves on the majority of test dates. Stems and leaves of ‘John Creech’ survived to at least −26C (−15F) and −21C (−6F), respectively, in January 2001. ‘Edward Goucher’ and ‘Confetti’ had the least hardy stems and leaves, respectively. Stems of ‘Edward Goucher’ survived to at least −16C (3F) in January 2000, and ‘Confetti’ leaves survived to only −14C (7F) in December 2000. Abelia × grandiflora consistently ranked among the first to attain cold hardiness in the fall and among the last to lose cold hardiness in the spring in both test seasons. Stems were equal in hardiness or hardier than leaves on the majority of test dates in both test seasons. Laboratory results were consistent with field observations, but often differed from published hardiness ratings. Differences in lowest survival temperatures and attainment and retention of cold hardiness closely followed temperature fluctuations just prior to sampling dates.</jats:p

Interspecific and Intergeneric Hybridization in Baptisia and Thermopsis

Interspecific and intergeneric crosses were performed between species in the genera Baptisia and Thermopsis with the goal of creating hybrids with the best qualities of both parents. Baptisia australis (L.) R. Br. was used as both the male and female parent in intergeneric crosses. Thermopsis chinensis Benth. ex S. Moore, T. lupinoides (L.) Link, and T. villosa Fernald &amp; B.G. Schub. were used as male and female parents in both interspecific and intergeneric crosses. Pollen was collected from B. alba (L.) Vent., B. bracteata Muhl. ex Elliott, and B. lanceolata (Walt.) Ell. and used to make interspecific and intergeneric crosses. Putative hybrids were obtained from both interspecific and intergeneric crosses. Interspecific crosses produced a higher percentage of pollinations resulting in seed set and the number of seeds per pollination than intergeneric crosses. Morphological differences between parent species and progeny were evident in putative hybrids resulting from intergeneric crosses between T. villosa and B. australis and T. villosa and B. alba. Most putative hybrids bloomed during the second year after germination. Because seedlings could be obtained from both interspecific and intergeneric crosses, hybrids within and between the genera Baptisia and Thermopsis are feasible. The Fabaceae family contains 670–750 genera and 18,000–19,000 species. Baptisia (commonly called false or wild indigo) and Thermopsis (commonly named false lupine) of the Fabaceae belong to the tribe Thermopsidae, which comprises 46 species in six genera. All species in Thermopsis and Baptisia are herbaceous; they are the only two genera in Thermopsidae that do not have woody species. Thermopsis contains 23 species and has a wide-spread distribution with species endemic to Asia and much of temperate North America. Although Thermopsis is considered to have originated in central Asia, T. chinensis Benth. ex S. Moore and T. fabacea (Pallas) Candole are thought to have originated in North America and migrated over the Bering Land Strait to Asia. Three Thermopsis species, T. fraxinifolia Nutt. ex M.A. Curtis, T. mollis (Michx.) M.A. Curtis ex A. Gray, and T. villosa Fernald &amp; B.G. Schub., are native to the southeastern United States. Baptisia contains 15–17 species that are endemic to the southeastern and midwestern United States.</jats:p