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United States Department of Agriculture

Agricultural Research Service

2009 Annual Report

1a.Objectives (from AD-416)
Objective 1: Develop and coordinate biological control programs to achieve sustained suppression of Lepidium draba L. (Brassicaceae), Centaurea spp., Hieracium spp. (Asteraceae), Tamarix spp. (Tamaricaceae), Euphorbia esula L. (Euphorbiaceae), and other invasive plants by: 1a) determining the systematics and phylogeography of target species; 1b) identifying, testing and releasing new arthropods and plant pathogens alone and in synergistic combinations; 1c) assessing rates of establishment, population growth, dispersal and impacts of agents on target weeds, native plants, and associated soil microbial communities; and 1d) integrate biological control agents with chemical, cultural and other control methods to enhance the impact of weed management programs. Objective 2: Identify key factors and mechanisms affecting the success of biological control programs and plant invasions including: 2a) genetic and phenotypic traits of target weeds that determine the success of invasive plant species in distinct ecological regions; 2b) genetic and phenotypic traits of biological control agents affecting their establishment, population growth, and impact; 2c) the biotic, edaphic, and environmental factors and mechanisms affecting weed establishment and expansion, and success of biological control agents; and 2d) integrate population information from Objectives 1 and 2 with remote sensing imagery and other spatial/temporal databases to develop spatial models of weed invasion risk.

1b.Approach (from AD-416)
Exotic invasive weeds cause about $27 billion annually in economic losses in addition to environmental impacts ranging from displacement of species of conservation concern to altered ecosystem functions. Biologically-based control methods can provide cost-effective, sustainable means of limiting the adverse impacts of invasive plants over extensive rangeland and natural areas. Our studies will focus on increasing the success of biological control efforts through better scientific understanding of: mechanisms underlying both the impact of agents and patterns of weed and agent dispersal; genetic variation within target weeds and biological control agents; evolutionary relationships of target weeds and agents; synergisms between plant pathogens, deleterious microbes, and arthropod agents; direct and indirect effects of biological control introductions on nontarget organisms in a risk analysis context; environmental factors affecting weed and biological control agent dynamics and invasion risk; and follow-on effects following suppression of weeds by biological control agents. Anticipated products of our project include new biological control agents, improved systematic and phylogeographic understanding of target weeds and control agents, improved systems for assessing and monitoring weed and insect populations; elucidation of factors and mechanisms limiting the establishment and success of biological control releases. This will benefit land managers, users of public lands, the general public, and the scientific community in the fields of invasive plant ecology, systematics and biological control.

3.Progress Report
Taxonomy: Perennial pepperweed (Lepidium latifolium) and dalmatian toadflax (Linaria dalmatica) are major invasive plants in western states, and in both cases, it is unclear to botanists worldwide which of the many species names they correlate with in Eurasia. Without correct knowledge of our invasives’ names, it is difficult to design a biological control program and search for biological control agents that will attack our invasion. We collected and started analysis of DNA from USA and Asia in order to compare DNA and answer these taxonomic questions.

Saltcedar (Tamarix spp.) biological control: A new agent (galling moth) was imported to USA to begin rearing and host-specificity studies. Survival during shipment needs to be improved. Whitetop (Lepidium draba): We began rearing studies to see if a newly proposed weevil agent will reproduce with an existing, similar cabbage seed pod weevil, which would preclude its use as a biological control agent.

New soilborne diseases of white top: We discovered a significant stem, crown and root rot disease on whitetop: Phoma lingam. This indicates that establishment of root-feeding insects would likely invoke highly effective insect/plant pathogen synergisms at sites such as the one where this and two foliar pathogens were found.

Restoration after invasion: We began an experiment to examine how annual grasses affect perennial grass establishment in restoration seeding, and also instigated a collaboration with staff at Theodore Roosevelt National Park, ND, to examine how annual forbs may promote success in restoration seedings. These projects will be an important source of information about how we can maximize the success of restoration seedings, and will also provide basic scientific data on annual and perennial life histories, facilitation, and competition.

1. Phenotypic and molecular characterization of leafy spurge and white top pathogens. The plant pathogens causing three previously unreported diseases of leafy spurge (Euphorbia esula) and whitetop (Lepidium draba) were identified, characterized and proven to be pathogenic. An isolate of Agrobacterium tumefaciens causing crown gall of leafy spurge in Hungary was classified as belonging to biovar 2 and the causal agents of two leaf spot diseases of whitetop were identified as Cercospora bizzozeriana and Alternaria brassicae. In the former case, this is the first report on this weed in the USA and in the latter case, in the world.

2. Disease affecting post-biocontrol restoration of native species. Completed studies which showed that species of the soilborne fungus Fusarium were the cause of disease or death of at least 7 forb species, which had experienced a high frequency of attrition after being transplanted for native plant restoration at several former leafy spurge infestation sites where successful biological control had been achieved. This is the first plant pathological study of disease occurring on native forbs in restoration plots. It provides an explanation for the reports of the failure of the forb community diversity to recover post-biocontrol. The simultaneous negligible disease levels on native grasses in the plots also explain how grass species are relatively unaffected by biocontrol. An additional impact of the work is that managing disease should be a consideration in restoration programs post-biocontrol and in general.

3. Determined identity of unknown invasive Casuarina (sheoak) species: Three Casuarina tree species, C. glauca, C. cunninghamiana, and C. equisetifolia, native to Australia, are severely invasive in Florida, USA. Many Florida Casuarina trees are considered unidentifiable. ARS scientists in Sidney, MT collected tissue from over 500 trees from Australia and Florida and compared their DNA fingerprints. In Florida, many trees are hybrids between C. glauca and C. equisetifolia. In Australia, scientists found three parental species, but no evidence of hybridization. The presence of novel hybrids in the Florida invasion increases genetic diversity in the invasion and may enhance evolution of invasive traits. Novel Casuarina hybrids in Florida have no coevolutionary history with any insects or diseases, which may be problematic for biological control efforts.

Review Publications
Gaskin, J.F., Kazmer, D.J. 2009. Introgression between saltcedars (Tamarix chinensis and T. ramosissima) in the USA invasion. Biological Invasions. 11(5):1121-1130.

Ayres, D., Ryan, F.J., Grotkopp, E., Bailey, J., Gaskin, J.F. 2008. Tumbleweed (Salsola, secion Kali) Species and Speciation in California. Biological Invasions. 11(5):1175-1187.

Caesar, A.J., Lartey, R.T. 2008. First report of crown gall caused by Agrobacterium tumefaciens on Euphorbia esula/virgata in Europe. Plant Disease 92(12):1710-1710.

Caesar, A.J., Lartey, R.T., Berner, D.K., Souissi, T. 2009. First report of leaf spot caused by Cercospora bizzozeriana on Lepidium draba in the United States. Plant Disease. 93(1):108-108.

Shi, W., Pan, B., Gaskin, J.F., Kang, X. 2009. Morphological Variation and Chromosome Studies of Calligonum mongolicum and C. pumilum (Polygonaceae). Nordic Journal of Botany. 27(2):81-85.

Gaskin, J.F., Wheeler, G.S., Purcell, M., Taylor, G. 2009. Molecular evidence of hybridization in Florida's sheoak (Casuarina spp.) invasion. Molecular Ecology. 18(15):3216-3226.

Friedman, J., Rolle, J., Gaskin, J.F., Pepper, A., Manhart, J. 2008. Latitudinal variation in cold hardiness in introduced Tamarix and native Populus. Evolutionary Applications. 1(4):598-607.

Caesar, T., Busscher, W.J., Novak, J.M., Gaskin, J.F., Kim, Y. 2008. Effects of Polyacrylamide and Organic Matter on Microbes associated to Soil Aggregation of Norfolk Loamy Sand. Applied Soil Ecology. 40(2):240-249.

Caesar, A.J., Lartey, R.T. 2009. First Report of a Leaf Spot Caused by Alternaria brassicae on the Invasive Weed Lepidium draba in North America. Plant Disease. 93(8):846-846.

Caesar, T., Lartey, R.T., Solberg Rodier, L.L., Caesar, A.J. 2009. Effects of Basidiomycete laccase on Cercosporin. Journal of Plant Pathology. 91(2):347-355.

Last Modified: 1/30/2015
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