Richard T. Olsen

Plant breeding for harmony between agriculture and the environment

Plant breeding programs primarily focus on improving a crops environmental adaptability and biotic stress tolerance in order to increase yield. Crop improvements made since the 1950s – coupled with inexpensive agronomic inputs, such as fertilizers, pesticides, and water – have allowed agricultural production to keep pace with human population growth. Plant breeders, particularly those at public institutions, have an interest in reducing agricultures negative impacts and improving the natural environment to provide or maintain ecosystem services (eg clean soil, water, and air; carbon sequestration), and in creating new agricultural paradigms (eg perennial polycultures). Here, we discuss recent developments in, as well as the goals of, plant breeding, and explain how these may be connected to the specific interests of ecologists and naturalists. Plant breeding can be a powerful tool to bring “harmony” between agriculture and the environment, but partnerships between plant breeders, ecologists, urban plann...

Ulmus americana (Ulmaceae) is a polyploid complex.

PREMISE OF THE STUDY Exotic diseases are threatening many North American tree species, and management of diseases requires understanding the biology of the host as well as the pathogen. Ulmus americana is a widespread dominant tree of eastern North America that has been widely planted as an ornamental and shade tree. Populations of the species have suffered heavy mortality from Dutch elm disease, caused by an introduced fungus. Ulmus americana is generally reported to be tetraploid, but the discovery of triploid trees in cultivation suggested that lower ploidy levels may exist in the wild, so the species was surveyed for nuclear DNA content. METHODS Ploidy level was estimated by flow cytometry for 81 individuals from wild populations of U. americana from throughout the range of the species and for four cultivated trees of interest. KEY RESULTS Most specimens were tetraploid, as previously reported for the species, but 21% of the wild trees sampled were diploid, a ploidy level not previously confirmed for the species. Tetraploids are found throughout the range of the species. Diploids are most common on the Atlantic coastal plain, Cumberland Plateau, and in southern Ohio, but isolated diploids were also found in central Texas, Oklahoma, and eastern Missouri. Diploids and tetraploids grew in proximity in several areas, but no wild triploids were found in the course of this survey. CONCLUSIONS The species is genetically heterogeneous, but further research is needed to understand the origin and relations of the different ploidy levels. Understanding the ploidy situation in U. americana will be important in the search for further genotypes that are resistant to Dutch elm disease.

Development of polymorphic genic-SSR markers by cDNA library sequencing in boxwood, Buxus spp. (Buxaceae).

Premise of the study: Genic microsatellites or simple sequence repeat (genic-SSR) markers were developed in boxwood (Buxus taxa) for genetic diversity analysis, identification of taxa, and to facilitate breeding. Methods and Results: cDNA libraries were developed from mRNA extracted from leaves of Buxus sempervirens ‘Vardar Valley’ and sequenced using the Illumina MiSeq system. Approximately 11.9 million base pairs of sequence data were examined and 845 genic-SSRs were identified, including 469 dinucleotide, 360 trinucleotide, seven tetranucleotide, one pentanucleotide, and eight hexanucleotide repeats. Primer pairs were designed for 71 selectively chosen genic-SSRs containing trinucleotide repeat motifs and were used to amplify the corresponding loci in 18 diverse boxwood accessions. Twenty-three primer pairs amplified polymorphic loci, with two to 10 alleles per locus. Conclusions: These novel polymorphic genic-SSR markers will aid in evaluating genetic diversity of boxwood germplasm and allow verification of hybrids and cultivars for breeding programs.

Use of Mycelium and Detached Leaves in Bioassays for Assessing Resistance to Boxwood Blight

Boxwood blight caused by Calonectria pseudonaviculata is a newly emergent disease of boxwood (Buxus spp. L.) in the United States that causes leaf drop, stem lesions, and plant death. A rapid and reliable laboratory assay that enables screening hundreds of boxwood genotypes for resistance to boxwood blight is needed to enable breeding and selection of resistant cultivars. Using eight boxwood cultivars with differing susceptibilities, we examined parameters for a screening assay comparing whole plant inoculation with detached leaf inoculation, use of mycelium versus spores as the inoculum, comparison of times of the year for inoculation, and comparison of two leaf inoculation methods. Inoculation of detached leaves gave comparable results to inoculation of whole plants when compared across genotypes, although the detached leaf assay resulted in greater percentages of symptom expression. The time of year of plant inoculation (spring, summer, or winter) did not affect the relative expression of symptoms among the most resistant and susceptible genotypes. Inoculating plants with mycelium was as effective as spore inoculation for causing disease symptoms and allowed us to distinguish the more resistant genotypes, yet mycelium inoculation was much easier to prepare in large quantities for multiple assays.

Ploidy Variation in Fraxinus L. (Oleaceae) of Eastern North America: Genome Size Diversity and Taxonomy in a Suddenly Endangered Genus

Premise of research. Ash (Fraxinus spp.), once dominant forest trees in eastern North America, are now endangered by the rapid spread of the emerald ash borer. Fraxinus is the target of conservation programs, but sampling genetic resources for conservation requires a knowledge of the taxonomy in order to ensure that genetically distinct groups are being conserved, and this has been hampered by serious disagreements about the taxonomy of North American Fraxinus. Polyploidy has been important in speciation in the genus, so ploidy level determination can help to establish natural species boundaries in the group. Methodology. Flow cytometry, calibrated with known chromosome counts, was used to assess genome size and infer ploidy for 303 accessions of Fraxinus spp., representing all 12 putative species recognized in the United States east of the hundredth meridian. Pivotal results. Monoploid genome size varied from 1Cx=0.725 for F. quadrangulata (sect. Dipetalae) to 1Cx=0.925 pg (sect. Melioides), and polyploidy was found in several species of sect. Melioides. Taxonomic separation of polyploid F. biltmoreana from the diploid F. americana and the recognition of F. profunda as a valid species are both strongly supported, but the results do not support separation of glabrous plants from F. biltmoreana as F. smallii. Both diploid and tetraploid populations were found in F. caroliniana. Fraxinus profunda proved to be octaploid, not hexaploid as previously reported. Conclusions. Further work is needed on F. biltmoreana, F. caroliniana, and F. pauciflora, wherein taxonomic concepts are still not well supported by the genetic data. Results indicate the importance of establishing an accurate taxonomy when undertaking conservation work. Conservation efforts in eastern North American Fraxinus are less likely to conserve the full scope of genetic diversity within the genus if only a few broadly defined species are recognized. It is critical that well-founded segregate species be taken into account.

Taxonomic revision of the genus Catalpa (Bignoniaceae)

A taxonomic revision of Catalpa (Bignoiaceae), a genus of perennial trees frequently used in horticulture as garden and street trees, is provided. Eight natural species and two hybrid species are recognized, four in sect. Catalpa, four in sect. Macrocatalpa, and two hybrid species in sect. Catalpa. Although C. punctata has been used for one of the tropical species, C. macrocarpa is the correct scientific name. Catalpa tibetica is synonymous with C. bignonioides, C. fargesii with C. bungei, and C. obovata with C. macrocarpa. Lectotypes are designated for: Bignonia cassinoides, Bignonia longisiliqua, Bignonia longissima, Catalpa Walter, Catalpa subsect. Corymbosae, Catalpa bignonioides var. kaempferi, Catalpa bungei, Catalpa bungei var. heterophylla, Catalpa bungei var. intermedia, Catalpa domingensis, Catalpa fargesii, Catalpa henryi, Catalpa ×hybrida, Catalpa ovata var. flavescens, Catalpa punctata var. lepidota, Catalpa purpurea, Catalpa syringifolia var. pulverulenta, Catalpa sutchuensis, Catalpa ×teasii, and Cumbulu. Second-step lectotypes are designated for: Catalpa duclouxii, Catalpa ekmaniana, Catalpa oblongata, Catalpa obovata, and Catalpa ovata. Neotypes are designated for: Bignonia triloba, Catalpa aureovittata, Catalpa bignonioides var. variegata, Catalpa ×erubescens, Catalpa ×erubescens f. purpurea, Catalpa ×galleana, Catalpa ×hybrida var. atropurpurea, Catalpa japonica, Catalpa syringifolia var. aurea, Catalpa syringifolia var. koehnei, Catalpa syringifolia var. nana, Catalpa ×teasiana, and Catalpa umbraculifera.

Validation of the Hybrid Flowering Cherry Prunus ×incam (Rosaceae)

Abstract The name Prunus ×incam Ingram ex R. Olsen & Whittemore is validated here. Introduced as a cultivated variety in 1947, Ingrams name Prunus ×incam has been in use as a nomen nudum in horticultural literature and the nursery trade for artificial crosses involving the parent taxa P. incisa Thunberg × P. campanulata Maximowicz. Prunus ×incam is an early flowering tree with two or three flowers in each persistent involucre, spreading sepals, and pink, deeply emarginate petals. Ingrams original introduction, the cultivated variety ‘Okamé,’ is the most widely grown form.