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Diversity and Management of Russian-Thistle (Salsola Tragus L.) in the Dryland Cropping Systems of the Inland Pacific Northwest

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Diversity and Management of Russian-Thistle (Salsola Tragus L.) in the Dryland Cropping Systems of the Inland Pacific Northwest DIVERSITY AND MANAGEMENT OF RUSSIAN-THISTLE (SALSOLA TRAGUS L.) IN THE DRYLAND CROPPING SYSTEMS OF THE INLAND PACIFIC NORTHWEST By JOHN FORREST SPRING A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY WASHINGTON STATE UNIVERSITY Department of Crop and Soil Science MAY 2017 © Copyright by JOHN FORREST SPRING, 2017 All Rights Reserved © Copyright by JOHN FORREST SPRING, 2017 All Rights Reserved To the Faculty of Washington State University: The members of the Committee appointed to examine the dissertation of JOHN FORREST SPRING find it satisfactory and recommend that it be accepted. _________________________________________ Drew J. Lyon, Ph.D., Chair _________________________________________ Ian C. Burke, Ph.D. _________________________________________ Eric H. Roalson, Ph.D. _________________________________________ Frank L. Young, Ph.D. ii ACKNOWLEDGEMENTS Thank you to all that contributed to the conduct of this work, and to the education of a would-be scientist: my advisor, Drew Lyon, and committee members, program technicians, professors, and fellow graduate students. iii DIVERSITY AND MANAGEMENT OF RUSSIAN-THISTLE (SALSOLA TRAGUS L.) IN THE DRYLAND CROPPING SYSTEMS OF THE INLAND PACIFIC NORTHWEST Abstract by John Forrest Spring, Ph.D. Washington State University May 2017 Chair: Drew J. Lyon Russian-thistle (Salsola tragus L.) is one of the most troublesome weed species in the low- and intermediate-precipitation dryland wheat-fallow cropping zones of the inland Pacific Northwest (PNW). High levels of morphological diversity typify the species on global, continental and regional scales. Previous research in California found this variability to encompass a largely cryptic complex of five distinct species in populations of Salsola in that state. Russian-thistle also exhibits high levels of morphological diversity in the inland PNW, suggesting that similar levels of genetic differentiation and population structure may be present in the region. A double-digest RAD-seq approach was used to characterize the genetic diversity and population structure of Russian-thistle in a sample of 94 individual plants collected across the wheat-fallow production region of eastern Washington and northeastern Oregon. Only one species (Salsola tragus sensu lato) was found. Multi-dimensional scaling, kernel-PCA-and- optimization population clustering, and Moran’s eigenvector mapping approaches all indicate the presence of a single, unstructured population across the region. High levels of standing genetic diversity were indicated in this population by expected multilocus heterozygosity of 0.35. iv Separate trials related to field weed management led to the first reported case of glyphosate resistance in Russian-thistle from Washington state. Dose response experiments conducted in greenhouse and field settings indicated 2.5 to 8-fold resistance to glyphosate in this accession. Variability in the magnitude of expressed glyphosate resistance appeared closely correlated with temperature conditions after application, with higher temperatures resulting in higher levels of expressed resistance. Resistance to glyphosate poses a substantial threat to successful weed control in chemical fallow in the PNW, which relies heavily on glyphosate. Field experiments were conducted to evaluate several pre-emergence herbicides for addition to glyphosate-only chemical fallow management programs in the wheat-fallow region. Initial results indicate that this approach has potential to improve efficacy of control and reduce selection pressure for glyphosate resistance in chemical fallow, but further experimentation is needed before robust field management recommendations can be developed. v TABLE OF CONTENTS Page ACKNOWLEDGEMENTS............................................................................................................iii ABSTRACT...................................................................................................................................iv TABLE OF CONTENTS................................................................................................................vi LIST OF TABLES..........................................................................................................................ix LIST OF FIGURES.........................................................................................................................x CHAPTER 1: Review of the Literature Dryland Cropping Zones of the Inland Pacific Northwest.........................................................1 Russian-thistle Description...........................................................................................................................3 History in North America....................................................................................................5 Biology and Ecology............................................................................................................5 Impacts.................................................................................................................................8 Control and Management...................................................................................................11 Herbicide Resistance..........................................................................................................14 Genetic Diversity...............................................................................................................15 Research Objectives...........................................................................................................19 Literature Cited.........................................................................................................................20 Tables and Figures....................................................................................................................25 vi CHAPTER 2: Russian-thistle Population Structure in the Dryland Cropping Region of the Inland Pacific Northwest Introduction...............................................................................................................................26 Materials and Methods Plant Material.....................................................................................................................30 Species Identification.........................................................................................................31 Library Preparation and Sequencing..................................................................................33 Genotyping and SNP Calling.............................................................................................34 Population Structure and Genetic Diversity......................................................................35 Results and Discussion.............................................................................................................36 Literature Cited.........................................................................................................................44 Tables and Figures....................................................................................................................49 CHAPTER 3: Glyphosate Resistant Russian-thistle in Washington State Introduction...............................................................................................................................54 Materials and Methods Plant Material.....................................................................................................................55 Greenhouse Dose-response Assay.....................................................................................56 Field Dose-response Assays..............................................................................................57 Data Analysis.....................................................................................................................59 Results and Discussion.............................................................................................................60 Literature Cited.........................................................................................................................64 Tables and Figures....................................................................................................................66 vii CHAPTER 4: Tank Mixes of Glyphosate and Soil Residual Herbicides for Extended Control of Russian-thistle in Chemical Fallow Introduction...............................................................................................................................70 Materials and Methods..............................................................................................................72 Results and Discussion.............................................................................................................74 Literature Cited.........................................................................................................................79 Tables and Figures.....................................................................................................................81 viii LIST OF TABLES Table 2.1. Selected summary metrics for SNP datasets.................................................................49 Table 3.1 Parameter estimates ± standard errors for fitted dose-response lines for greenhouse experiments....................................................................................................................................65
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