Neil O. Anderson

Invasiveness in wetland plants in temperate North America.

The spread of invasive taxa, includingLythrum salicaria, Typha × glauca, Myriophyllum spicatum, Phalaris arundinacea, andPhragmites australis, has dramatically changed the vegetation of many wetlands of North America. Three theories have been advanced to explain the nature of plant invasiveness. Aggressive growth during geographic expansion could result because 1) growth is more favorable under new environmental conditions than those of resident locales (environmental constraints hypothesis); 2) herbivores may be absent in the new locale, resulting in selection of genotypes with improved competitive ability and reduced allocation to herbivore defenses (evolution of increased competitive ability hypothesis); and 3) interspecific hybridization occurred between a new taxon and one existing in an area, resulting in novel phenotypes with selective advantages in disturbed sites or phenotypes that can grow under conditions not favorable for either parent (introgression/hybrid speciation hypothesis). A review of published literature found few studies that compare the growth and dynamics of invasive populations in their new range versus those in historic ranges. However, there is evidence that hydrologic alterations could facilitate invasions byTypha × glauca andPhalaris arundinacea and that increased salinity promoted spread ofTypha angustifolia (parental taxon) andPhlaris arundinacea and that increased salinity promoted spread ofTypha angustifolia (parental taxon) andPhragmites australis. The potential for reduced herbivory causing aggressive growth is greatest forLythrum salicaria. Introgressive hybridization is potentially a cause of invasiveness for all five species but has been established only forTypha × glauca andLythrum salicaria.

Conundrums of a complex vector for invasive species control: A detailed examination of the horticultural industry

Historically the horticultural industry has transformed the US landscape through intentional cultivar introductions and unintentional introductions of weeds, insects and plant diseases. While it has been demonstrated that the horticultural industry, in particular the ornamental subsector, is an important vector for the introduction and dispersal of invasive species, known invasive plants continue to be sold while new cultivars are introduced at an ever increasing rate. This study examines the horticultural trade as a vector for invasive species, its agents, and characterizes the complexity of the distribution channel. Numerous factors have contributed to the recent expansion in marketed cultivars, including technological, industry growth, and marketing developments. The result has been an increased and sophisticated consumer demand with a corresponding aggressive scouring of the planet for new crops, many of which are introduced into the market without sufficient testing for invasive tendencies. Traditional approaches to invasive horticultural crop control (regulation, self-regulation), which target players in the distribution channel before and/or after cultivar release, have had limited effectiveness and buy-in because these approaches do not address the industry’s complexities and economic incentives. Involvement and education of consumers may provide better oversight outcomes by addressing the moral hazard problem while acknowledging the key characteristics of the industry.

Trifluralin-mediated polyploidization of Rosa chinensis minima (Sims) Voss seedlings

Many diploid rose species and cultivars possess valuable traits that can be introgressed into modern tetraploid cultivars. Interspecific, interploidy crosses are possible, but triploid hybrids typically have limited fertility, hindering further breeding and selection. Tetraploidizing diploids before mating with tetraploids can alleviate fertility barriers. The efficiency of trifluralin was investigated for polyploidization of Rosa chinensis minima (2n = 2x = 14) seedlings. Treatments were trifluralin at 0.086% and 0.0086%, colchicine (0.5%), and distilled water and contained 2% dimethyl sulfoxide and a surfactant. Approximately 5 μl of the treatment solution was applied to the apical meristem of seedlings (N = 337, 82–85 per treatment) in the process of cotyledon expansion. Guard cell length, pollen diameter, and root tip squashes of rooted cuttings were used to detect polyploidy in meristematic layer (L)I, LII, and LIII, respectively. Trifluralin (0.086%) was the most effective treatment for polyploidization (LI 20.2%, LII 12.9%, LIII 12.9%), followed by trifluralin (0.0086%) (LI 10.6%, LII 7.1%, LIII 4.7%) and colchicine (LI 2.4%, LII 0%, LIII 0%). Polyploidization consistently occurred from LI inward. Polyploids as a group had reduced pollen stainability and a lower leaflet length to width ratio than diploids. In addition, two diploid seedlings were identified which produce 2n pollen. Considerations in selecting germplasm and generating somatically-induced polyploids from seedlings versus clones for use in breeding are discussed.

Selection strategies to reduce invasive potential in introduced plants

SummaryThe crop domestication process is examined from plant collection to product release for various junctures at which deliberate breeding, selection, and crop transformation may occur to prevent invasive potential. Four primary juncture opportunities for research on techniques and development of selection procedures for non-invasiveness include: The Plant Exploration Phase, Initial Trial Phase, Fast-Tracking Phase, Selection and Improvement Phase. Avoiding the collection of germplasm that appears weedy during plant exploration is an obvious, yet cost-effective way to reduce invasiveness in a selection program. During initial trials, comparing genotypic differences in traits related to invasiveness should allow plant breeders to identify cultivars that pose the least risk before undertaking comprehensive field trials. Genotypes with high commercial value, considered candidates for “fast-tracking”, should only advance quickly to product release if they exhibit a minimum level of invasive risk, i.e., species with low dispersal capacity and that have little potential to impact ecosystems. Fast-growing taxa, those with high seed production, ones likely to be rapidly dispersed by wind, animals, water or people, and others that can significantly alter nutrient or light levels are examples of species that should not be “fast-tracked”. Field trials that have typically been used to evaluate performance of genotypes across a broad range of cultivated environmental conditions need to be expanded to adequately evaluate invasive potential during the selection and improvement phase. Testing in environments that mimic conditions where introductions could naturalize is crucial, as are evaluations of competition with indigenous species. The time and resource investment needed to conduct adequate trials at this stage is potentially very high; more research is needed to ensure the trials conducted are targeting important information gaps for decision-making. Additional research is also needed to develop modeling approaches that effectively forecast long-term dynamics of introductions and to assist in developing field testing priorities. Minimizing invasive potential could significantly reduce introductions that cause inadvertent damage to landscapes and ecosystems. The strategy proposed here will require further development, especially in the context of understanding and assessing risks of pre- and post-release strategies for minimizing damage from invasive species.

A non-invasive crop ideotype to reduce invasive potential

SummaryIn plant breeding programs, qualitative and quantitative traits confer market value and, thus, constitute the basis for developing breeding criteria during crop domestication. Some traits such as high male/female fertility are advantageous in the wild and could enable the evolution of cultivated crops into invasive weeds. Other traits, e.g. sterility, are not expected to confer invasiveness. To date there has been very limited involvement in invasion risk assessment by plant breeders. Thus, in this paper we propose that trait-based selection of potential crop species be coupled with species design in the creation of a “non-invasive crop ideotype” as an avenue to reduce invasiveness during domestication. The non-invasive crop ideotype embodies the ideal characteristics for a crop to excel in cultivated environment(s) but minimizes the likelihood it will establish and spread in non-cultivated environments, constituting the underlying foundation for all breeding objectives, choice(s) of breeding methodologies, and propagation techniques for non-invasive crop release. Using ornamental (floriculture) horticultural crops as an example, we identify 10 traits to be used individually or in combination to reduce invasiveness while retaining commercial value: reduced genetic variation in propagules, slowed growth rates, non-flowering, elimination of asexual propagules, lack of pollinator rewards, non-shattering seed, non-fleshy fruits, lack of seed germination, sterility, and programmed death (apotopsis). A non-invasive crop ideotype would constitute the underlying foundation for all breeding objectives, the choice(s) of breeding methodologies, and propagation technique(s). The ideotype should be flexible and should adjust to species- and crop-specific traits to account for the intended use. For example, development of sterile cultivars may have negligible effects in reducing invasiveness if the crops spread vegetatively. A non-invasive crop ideotype may increase the direct participation of plant breeders, who are the professionals directly involved in the collection, development and release of new crops, in reducing the invasive potential of ornamental crops. Future research is required to determine the feasibility of incorporating each trait into various crops, use of classical or molecular techniques for creation of non-invasive crops, trait stability (lack of genotype × environment interaction over years and locations), consumer acceptance, and long-term viability.

Minnesota horticultural industry survey on invasive plants

SummaryHorticultural commerce of ornamental plants has been the source of many of our most troublesome plant invaders worldwide. The purpose of this research was to document the knowledge gap of industry perspectives and knowledge of invasive ornamental crops by surveying industry professionals in the Midwest region of the U.S. (primarily in the state of Minnesota). An invasive plant survey was created to assess this information and was mailed to n = 500 individuals and companies randomly chosen from the Minnesota Nursery and Landscape Association (MNLA) membership, which included wholesale/retail nurseries, landscape design, installation & maintenance firms, and retail garden centers. A total of n = 167 surveys (33.4%) were returned and analyzed. A majority of respondents, 62%, felt that the invasive plant issue was very important and 89% tried to direct their customers away from potentially invasive plants. Many respondents, 76%, indicated that they were responsible for educating their customers about invasive ornamental plants. Sixty-nine percent said that they would not sell a plant if it was potentially invasive; however, 57% indicated that this would be true if a competing business was selling the plant. Respondent’s knowledge about specific invasive plants varied from 75% to 89% on the identification of three terrestrial invasive plant crops. Far less, 20% and 21%, were able to identify Butomus umbellatus and Salvinia molesta, respectively, two invasive aquatic species. When asked about regulation of invasive ornamental crops, 43% preferred national, state, or USDA regulation while 22% felt industry self-regulation was best, and 21% approved of private regulation. Opportunities exist for educating horticulture industry professionals about invasive plants and providing information to the public through commercial businesses.

Competive ability of invasive Miscanthus biotypes with aggressive switchgrass

Miscanthus (Miscanthus sinensis Anderss. [Poaceae]) is an ornamental and invasive grass native to Asia that has naturalized in several areas of the Middle Atlantic United States. Predicting how likely miscanthus is to become invasive in other areas of the US is a concern of ecologists and horticulturists. The objective of this study was to measure the competitive ability of miscanthus with an aggressive native grass, switchgrass (Pancium virgatum L. [Poaceae]), in order to show which grass would be more likely to dominate when the two species were grown together. Although switchgrass is a smaller plant than miscanthus, in this greenhouse experiment it was significantly taller and had more vegetative and flowering culms than miscanthus. Miscanthus however, was a stable competitor and did not significantly change in shoot or root dry weight as 2 and 4 switchgrass plants replaced the respective number of miscanthus plants in each treatment. When miscanthus biotypes from four locations were compared, the Pennsylvania biotype was significantly larger and more competitive with switchgrass than was the Washington, DC biotype. As switchgrass plants were replaced with miscanthus, the shoot and root dry weights of the remaining switchgrass plants increased significantly, showing a higher competitive ability of switchgrass. Despite the fact that switchgrass was more competitive with itself than miscanthus, the highest overall dry weight per treatment contained eight switchgrass plants. Miscanthus showed stable, competitive growth when planted together with switchgrass and it is predicted to likely do the same in a field setting.

How many marker loci are necessary? Analysis of dominant marker data sets using two popular population genetic algorithms

The number of marker loci required to answer a given research question satisfactorily is especially important for dominant markers since they have a lower information content than co-dominant marker systems. In this study, we used simulated dominant marker data sets to determine the number of dominant marker loci needed to obtain satisfactory results from two popular population genetic analyses: STRUCTURE and AMOVA (analysis of molecular variance). Factors such as migration, level of population differentiation, and unequal sampling were varied in the data sets to mirror a range of realistic research scenarios. AMOVA performed well under all scenarios with a modest quantity of markers while STRUCTURE required a greater number, especially when populations were closely related. The popular ΔK method of determining the number of genetically distinct groups worked well when sampling was balanced, but underestimated the true number of groups with unbalanced sampling. These results provide a window through which to interpret previous work with dominant markers and we provide a protocol for determining the number of markers needed for future dominant marker studies.

Congruity backcrossing as a means of creating genetic variability in self pollinated crops: Seed morphology of Phaseolus vulgaris L. and P.acutifolius A.Gray hybrids

SummarySeeds of early generations of three reciprocal congruity-backcross (CBC) pedigrees, developed by backcrossing Phaseolus vulgaris-P. acutifolius hybrids to each of the parent species in alternate generations, exhibited a preponderance of traits (size, shape, color, and pattern) of the cytoplasmic parent. The large size of ‘Red Cloud’ (V1), the P. vulgaris parent common to all of the pedigrees, dominated pedigrees with V1 as the cytoplasmic parent, while the small size and rounded or square shapes of the tepary parents, wild P. acutifolius var. acutifolius PI 263590 or G400445 (A19), wild P. acutifolius var. latifolius PI 406622 (A10), or cultivated P. acutifolius var. latifolius ‘Serowi’ PI 319443 (A9), were the majority phenotypes when P. acutifolius was the cytoplasmic parent. Continuing through the second cycle of CBC, that is the second backcross with each of the parent species or the fourth backcross, began an amelioration of the apparent cytoplasmic effect on gene expression, as reciprocal pedigrees became more alike, usually with intermediate expression of parental traits or the appearance of new traits. The large seed size of V1 was recovered in hybrids with P. acutifolius cytoplasm and the kidney shape of V1 became rare in hybrids with P. vulgaris cytoplasm. Although the tepary-bean parents represented two subspecies and both cultivated and wild P. acutifolius, the three sets of reciprocal-hybrid pedigrees with P. vulgaris ‘Red Cloud’ are surprisingly similar. It may be that the ‘exotic’ parent used to develop a CBC pedigree should be selected more for combining ability in the interspecific cross than for specific economic traits. While the number of generations (six or more) required to produce fertile, intermediate CBC hybrids (that did not require embryo rescue) may preclude routine use of this method by practical plant breeders, the crossability of advanced hybrids with both parental species and the amount of variability apparent in advanced-hybrids progenies suggests that CBC would be valuable for maintaining ‘exotic’ germplasm in immediately useful forms.

Population genetic structure of N. American and European Phalaris arundinacea L. as inferred from inter-simple sequence repeat markers

Phalaris arundinacea L. (reed canarygrass) has become one of the most aggressive invaders of North American wetlands. P. arundinacea is native to temperate N. America, Europe, and Asia, but repeated introductions of European genotypes to N. America, recent range expansions, and the planting of forage and ornamental cultivars complicate the resolution of its demographic history. Molecular tools can help to unravel the demographic and invasion history of populations of invasive species. In this study, inter-simple sequence repeat markers were used to analyze the population genetic structure of European and N. American populations of reed canary grass as well as forage and ornamental cultivars. We found that P. arundinacea harbors a high amount of genetic diversity with most of the diversity located within, as opposed to among, populations. Cluster analyses suggested that current populations are admixtures of two formerly distinct genetic groups.