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Dynamics of the Sweetpotato Potyvirus Aphid Pathosystem in Louisiana

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Dynamics of the Sweetpotato Potyvirus Aphid Pathosystem in Louisiana Louisiana State University LSU Digital Commons LSU Doctoral Dissertations Graduate School 2012 Dynamics of the sweetpotato potyvirus aphid pathosystem in Louisiana Everlyne Nafula Wosula Louisiana State University and Agricultural and Mechanical College, [email protected] Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_dissertations Part of the Plant Sciences Commons Recommended Citation Wosula, Everlyne Nafula, "Dynamics of the sweetpotato potyvirus aphid pathosystem in Louisiana" (2012). LSU Doctoral Dissertations. 1088. https://digitalcommons.lsu.edu/gradschool_dissertations/1088 This Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Doctoral Dissertations by an authorized graduate school editor of LSU Digital Commons. For more information, please [email protected]. DYNAMICS OF THE SWEETPOTATO POTYVIRUS APHID PATHOSYSTEM IN LOUISIANA A Dissertation Submitted to the Graduate Faculty of the Louisiana State University and Agriculture and Mechanical College in partial fulfillment of the requirements for the degree of Doctor of Philosophy in The Department of Plant Pathology and Crop Physiology by Everlyne Nafula Wosula B Sc. Jomo Kenyatta University of Agriculture and Technology, 1998 M Sc. Jomo Kenyatta University of Agriculture and Technology, 2007 December 2012 DEDICATION This dissertation is dedicated to my son Moses Kipseete and my husband Erastus Chepkwony for their love and support, to my beloved grandparents Dina Nasipwondi and Jeremiah Wosula who taught me the values of life and the importance of education. I also dedicate this work to my mum, my sister Tatiana, my brother Phillippe, my aunt Charity and to all my extended family members for their prayers, love and moral support. ii ACKNOWLEDGEMENTS I would like to sincerely thank my advisors Dr. Christopher A. Clark and Dr. Jeffrey A. Davis for their invaluable guidance, support, advice, patience, kindness and motivation throughout my doctoral studies. I am also very grateful for the efforts, inputs and advice given by my committee members Dr. Rodrigo Valverde, Dr. Don LaBonte and Dr. Tara Smith. This work was accomplished with financial support from the Department of Plant Pathology and Crop Physiology, Department of Entomology, Louisiana State University Agricultural Center, the Louisiana State University Graduate School, the United States Department of Agriculture, Specialty Crop Research Initiative Grant number 2009- 51181-06071, and the Louisiana Sweet Potato Commission. I would like to express my sincere thanks to Dr. Lawrence E. Datnoff the head of the Department, the faculty, staff and graduate students of the Department of Plant Pathology and Crop Physiology for their support, motivation and advice during my studies. My appreciation and gratitude goes also to Dr. Timothy Schowalter the head of the Department, the faculty, and staff of the Department of Entomology for their support during my studies. I am very grateful and indebted to Mary Hoy for her kindness, patience, guidance and mentorship on laboratory techniques and use of equipment. I also would like to sincerely thank Mary Hoy, Rebecca Sweany, Arthur Richter, Daria Datnoff and Satvika Uppu for their tireless efforts to assist me with my field and laboratory experiments. I also thank Remmy Kasili for his support, guidance and advice that enabled me to apply and be accepted at LSU for my doctoral studies. I am also very grateful to all my friends for their friendship and moral support. iii TABLE OF CONTENTS DEDICATION ................................................................................................ ii ACKNOWLEDGEMENTS ........................................................................... iii LIST OF TABLES ........................................................................................ vii LIST OF FIGURES ..................................................................................... viii ABSTRACT .................................................................................................... 1 CHAPTER 1: INTRODUCTION .................................................................. 3 1.1 Justification ............................................................................................................... 7 1.2 Objectives .................................................................................................................. 7 CHAPTER 2: LITERATURE REVIEW ........................................................ 8 2.1 Sweetpotato .............................................................................................................. 8 2.1.1 Origin and taxonomy ......................................................................................... 8 2.1.2 Morphology, anatomy and physiology .............................................................. 9 2.1.3 Distribution and economic importance............................................................ 10 2.1.4 Uses and nutritional value of sweetpotato ....................................................... 12 2.2 Sweetpotato viruses ................................................................................................ 13 2.2.1 Potyviruses (Potyviridae) ................................................................................ 14 2.2.2 Ipomoviruses (Potyviridae) ............................................................................. 18 2.2.3 Criniviruses (Closteroviridae) ......................................................................... 19 2.2.4 Begomoviruses (Geminiviridae)...................................................................... 20 2.3 Aphids as vectors of sweetpotato viruses ............................................................... 21 2.3.1 Distinguishing features and classification ....................................................... 23 2.3.2 Host specificity, location and recognition ....................................................... 23 2.3.3 Feeding behavior ............................................................................................. 24 2.3.4 Flight patterns of aphids .................................................................................. 25 2.3.5 Electronic monitoring of aphid probing/feeding behavior .............................. 26 2.4 Whiteflies as vectors of sweetpotato viruses.......................................................... 27 2.5 Wild hosts of sweetpotato viruses .......................................................................... 28 2.6 Detection methods for sweetpotato viruses ............................................................ 29 2.7 Yield loss due to sweetpotato viruses .................................................................... 31 2.8. Management of sweetpotato viruses ..................................................................... 31 CHAPTER 3: EFFECT OF HOST PLANT, APHID SPECIES, AND VIRUS INFECTION STATUS ON TRANSMISSION OF SWEET POTATO FEATHERY MOTTLE VIRUS ...................................................................... 33 3.1 Introduction ............................................................................................................ 33 3.2 Materials and methods ........................................................................................... 36 iv 3.2.1 Host plants ....................................................................................................... 36 3.2.2 Virus inoculum ................................................................................................ 37 3.2.3 Aphid colony ................................................................................................... 37 3.2.4 NCM-ELISA assays ........................................................................................ 38 3.2.5 Establishment of virus acquisition and test plants ........................................... 39 3.2.6 Transmission experiments with Aphis gossypii and Myzus persicae .............. 40 3.2.7 Quantitative reverse transcription (qRT-PCR) assays ..................................... 42 3.3 Results .................................................................................................................... 43 3.3.1 Transmission experiments with Aphis gossypii and Myzus persicae .............. 43 3.3.2 SPFMV RNA titer in relation to aphid transmission ....................................... 45 3.4 Discussion .............................................................................................................. 46 CHAPTER 4: THE ROLE OF APHID ABUNDANCE, SPECIES DIVERSITY AND VIRUS TITER IN THE SPREAD OF SWEETPOTATO POTYVIRUSES IN LOUISIANA ............................................................... 52 4.1 Introduction ............................................................................................................ 52 4.2 Materials and methods ........................................................................................... 56 4.2.1 Aphid trapping ................................................................................................. 56 4.2.2 Sentinel plants.................................................................................................. 58 4.2.3 NCM-ELISA assays ........................................................................................ 59 4.2.4 Virus titer quantification .................................................................................. 60 4.2.5 Morning glory weeds
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