Although Hypericum androsaemum L. is a valuable landscape plant, the species can be weedy and potentially invasive in certain locations. Infertile, non-invasive cultivars of H. androsaemum with desirable ornamental features would be ecologically beneficial and valuable for the horticultural industry. The male and female fertility of 10 triploid H. androsaemum, developed with a combination of variegation and foliage colors, was investigated under greenhouse (controlled pollination) and field conditions (natural pollination). Male fertility was evaluated based on pollen viability tests (pollen staining and pollen germination). Female fertility was based on fruit set, seed set, germinative capacity of seeds, and number of seedlings produced for each flower. Although values for different measures of fertility varied among triploid clones, pollen germination was significantly reduced for all triploids and nine of the 10 triploids produced no viable seed. These results represent 100% failure of ≈171,000 potential fertilization events based on fertility levels of diploid controls. The remaining triploid clone produced two seedlings per flower compared with 260 seedlings per flower for the controls. However, the seedlings produced by the triploid clone died shortly after germination. This research documented that the triploid H. androsaemum tested are highly infertile with no measurable female fertility. These clones will provide ideal alternatives to fertile forms of H. androsaemum where invasiveness is a concern. These methods also provide a useful protocol for evaluating fertility of other taxa that are selected or developed as non-invasive cultivars of potentially weedy species.
Clara E. Trueblood, Thomas G. Ranney, Nathan P. Lynch, Joseph C. Neal and Richard T. Olsen
Thomas G. Ranney, Nathan P. Lynch, Paul R. Fantz and Paul Cappiello
Fothergilla L. spp. are valuable nursery and garden plants. However, clear differentiation among F. gardenii Murray, F. major Lodd., and potential hybrids can be difficult based solely on morphological characteristics. The objectives of this work were to verify and describe the existence of interspecific hybrids and to clarify the proper nomenclature for cultivars of Fothergilla that are commonly grown in the nursery industry. A comparison of morphological characteristics was made among diverse clones representing both species and potential hybrids. A combination of chromosome counts and DNA contents was used to clearly differentiate among F. gardenii (2n = 4x = 48), F. major (2n = 6x = 72), and hybrids (2n = 5x = 60). It was determined that the majority of cultivars represented in commerce were hybrids. Fothergilla ×intermedia Ranney and Fantz (hybrid fothergilla) is proposed as the name for these hybrids and is validated with a Latin diagnosis. Although certain morphological characteristics can be used to differentiate between F. gardenii and F. major, the hybrids tend to be intermediate and are particularly difficult to separate from F. major on the basis of appearance. The correct classification and nomenclature for 17 different taxa are presented.
Thomas G. Ranney, Connor F. Ryan, Lauren E. Deans and Nathan P. Lynch
Illicium is an ancient genus and member of the earliest diverging angiosperms known as the Amborellales, Nymphaeales, and Austrobaileyales (ANA) grade. These adaptable, broadleaf evergreen shrubs, including ≈40 species distributed throughout Asia and North America, are valued for diverse culinary, medicinal, and ornamental applications. The study of cytogenetics of Illicium can clarify various discrepancies and further elucidate chromosome numbers, ploidy, and chromosome and genome size evolution in this basal angiosperm lineage and provide basic information to guide plant breeding and improvement programs. The objectives of this study were to use flow cytometry and traditional cytology to determine chromosome numbers, ploidy levels, and relative genome sizes of cultivated Illicium. Of the 29 taxa sampled, including ≈11 species and one hybrid, 2C DNA contents ranged from 24.5 pg for Illicium lanceolatum to 27.9 pg for Illicium aff. majus. The genome sizes of Illicium species are considerably higher than other ANA grade lineages indicating that Illicium went through considerable genome expansion compared with sister lineages. The New World sect. Cymbostemon had a slightly lower mean 2C genome size of 25.1 pg compared with the Old World sect. Illicium at 25.9 pg, providing further support for recognizing these taxonomic sections. All taxa appeared to be diploid and 2n = 2x = 28, except for Illicium floridanum and Illicium mexicanum which were found to be 2n = 2x = 26, most likely resulting from dysploid reduction after divergence into North America. The base chromosome number of x = 14 for most Illicium species suggests that Illicium are ancient paleotetraploids that underwent a whole genome duplication derived from an ancestral base of x = 7. Information on cytogenetics, coupled with phylogenetic analyses, identifies some limitations, but also considerable potential for the development of plant breeding and improvement programs with this genus.
Thomas G. Ranney, Tracy H. Thomasson, Kristin Neill, Nathan P. Lynch and Mark Weathington
Aucuba have been cultivated for centuries and are valued as adaptable, broad-leaved, evergreen shrubs that also can have attractive, spotted variegations on the foliage. Improved understanding of the cytogenetics and heritability of specific traits, for specific clones and cultivars, can provide basic information to help facilitate the breeding and improvement of aucuba. The objectives of this study were to determine ploidy level and relative genome size of a diverse collection of species and cultivars of aucuba using flow cytometry and cytology and to make additional observations on heritability of spotted leaf variegation. Chromosome counts were 2n = 2x = 16 for Aucuba chinensis (A. omeiensis), 2n = 4x = 32 for A. japonica ‘Rozannie’, and 2n = 6x = 48 for A. sp. ‘Hosoba’. Relative 2C genome size for the 57 taxa varied from 13.8 pg for A. obcordata to 42.0 pg for A. ‘Hosoba’ and fell within three discrete groups consistent with cytotype. Genome size for diploid taxa (A. chinensis and A. obcordata) ranged from 13.8 to 21.0 pg, tetraploids (A. himalaica var. oblanceolata, A. japonica, and A. japonica var. borealis) ranged from 28.8 to 31.2 pg, and the first-ever reported hexaploids (A. ‘Hosoba’ and A. sp. – Vietnam) ranged from 40.5 to 42.0 pg. Unlike prior reports that indicated inheritance of spotted variegations were extranuclear genes that were maternally inherited, we found that the spotted leaf trait expressed in A. japonica ‘Shilpot’ appears to be a nuclear gene that is inherited in a quantitative fashion and not strictly maternal. These data provide an enhanced foundation for breeding improved aucuba.
Irene E. Palmer, Thomas G. Ranney, Nathan P. Lynch and Richard E. Bir
Rudbeckia L. are valuable nursery crops that offer broad adaptability and exceptional ornamental merit. However, there is little information on interspecific and interploid crossability and ploidy levels of specific cultivars. The objectives of this study were to determine the ploidy levels and relative DNA contents (genome sizes) of selected species and cultivars, to evaluate self-compatibility and crossability among species and ploidy levels, and to explore reproductive pathways in triploid R. hirta L. with the goal of facilitating future breeding endeavors and development of new hybrids. Reciprocal interspecific crosses were performed between R. hirta cultivars and R. fulgida Ait., R. missouriensis Engelm. ex C.L. Boynton & Beadle, and R. subtomentosa Pursh. as well as reciprocal interploid crosses among four R. hirta cultivars. A combination of relative DNA content analysis and chromosome counts was used to test for hybridity and to determine ploidy levels for selected species, cultivars, and interploid R. hirta F1 hybrids. Of the specific clones tested, R. subtomentosa and R. missouriensis were diploid, R. fuligida varieties were tetraploid, and R. hirta include both diploid and tetraploid cultivars. Mean 1Cx DNA content varied over 320% among species. The interploid R. hirta crosses produced triploids as well as pentaploids and hexaploids. Seedlings from open-pollinated triploid R. hirta appeared, based on diverse phenotypes and DNA contents, to be aneuploids resulting from sexual fertilization, not apomixis. Of the 844 seedlings from interspecific F1 crosses, only one individual, R. subtomentosa ×R. hirta, had a DNA content intermediate between its parents and was confirmed as the only interspecific hybrid. Although most taxa had low self-fertility, seedlings (with genomic sizes similar to their maternal parent) resulted after interspecific crosspollination, indicating that pseudogamy is one reproductive pathway in Rudbeckia species.