Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 2007 Alternative hosts of Phakopsora pachyrhizi in the Americas: an analysis of their role in the epidemiology of Asian soybean rust in the continental U.S. Oscar Pérez-Hernández Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Agricultural Science Commons, Agronomy and Crop Sciences Commons, and the Plant Pathology Commons Recommended Citation Pérez-Hernández, Oscar, "Alternative hosts of Phakopsora pachyrhizi in the Americas: an analysis of their role in the epidemiology of Asian soybean rust in the continental U.S." (2007). Retrospective Theses and Dissertations. 15097. https://lib.dr.iastate.edu/rtd/15097 This Thesis is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Alternative hosts of Phakopsora pachyrhizi in the Americas: an analysis of their role in the epidemiology of Asian soybean rust in the continental U.S. by Oscar Pérez-Hernández A thesis submitted to the graduate faculty in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Major: Plant Pathology Program of Study Committee: Xiao Bing Yang, Major Professor Mark L. Gleason Eugene S. Takle Iowa State University Ames, Iowa 2007 UMI Number: 1446133 UMI Microform 1446133 Copyright 2007 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, MI 48106-1346 ii I dedicate this work to God, for my life. To my daughter, Daphne Gabriela, who, someday, when she can read and see her name written on this page, knows of Dady’s love for her. <Tú te convertiste en una de mis mayores motivaciones desde el momento en el que supe que existías. Te quiero mucho hija>. To my parents, Felicitas and Miguel, who have always supported, encouraged, and trusted me, and who, despite their limited education, knew how to inculcate in myself, discipline, good values, and the spirit to be someone in life. <Ustedes son los cimientos sobre los que están fundados mi carácter y mi vida; han sido y serán siempre mi motivación. Les dedico este esfuerzo con todo mi amor y cariño>. To my brothers: Hortencia, Nahúm, Alejandro, Arsenio, Miguel and Minerva, and to my nephews Benjamín, Edson and Joel, for their love. To all relatives to whom a link of love, trust, hope, and caring keeps me joined. To my Major Professor, Dr. Xiao-Bing Yang iii TABLE OF CONTENTS ABSTRACT………………………………………………………………………… v CHAPTER 1. GENERAL INTRODUCTION………………………………………. 1 Thesis organization………………………………………………………………………………………………………………………………. 1 Introduction…………………………………………………………………………………………………………………………………………….... 1 References………………………………………………………………………………………………………………………………………………... 4 CHAPTER 2. LITERATURE REVIEW…………………………………………….. 7 General information on the life cycle pattern of a rust fungus……..………………….……………….. 7 The disease: soybean rust………………………………………………………………………………………………………………….. 7 Causal agents……………………………………………………………………………………………………………………………… 7 Cycle, infection process and infection components…………………………………………………. 8 Symptoms…………………………………………………………………………………………………………………………………….. 9 Epidemiology…………………………………………………………………………………………………………………………….... 9 Current world distribution of soybean rust…………………………………………………………………… 10 Current distribution of soybean rust in the Americas…………………...………….……………… 11 The pathogen: Phakopsora pachyrhizi……………………………………………………………………………………….. 12 Morphology and taxonomy…………………………………………………………………………………………………. 12 Host range of Phakopsora pachyrhizi…………………………………………………………………………….. 13 The host (s):……………………………………………………………………………………………………………………………………………... 17 Soybean: the economically important host………………………………………………………………….... 17 Growth and development of soybean………………………….…………………………………………………... 17 Kudzu: an additional host component in the soybean rust pathosystem………………….…. 17 Origin, botanical description and taxonomy…………………………………...…………………………… 18 Habitat……………………………………………………………………………………………………………………………………………. 19 History and distribution of kudzu in the U.S.……………………………………………………………… 20 Green leaf area index: definitions and usefulness………………………………………………………………….. 20 Duration of the growing season of some suitable hosts of P. pachyrhizi………………..…... 22 References…………………………………………………………………………………………………………………………………….…………... 24 iv CHAPTER 3. KUDZU (Pueraria montana var. lobata) PHENOLOGY AND ITS IMPLICATIONS FOR OCCURRENCE AND SPREAD OF ASIAN SOYBEAN RUST IN THE U.S………………………………………………………………….. 36 Abstract…………………………………………………………………………………………………………………………………………………….... 36 Introduction…………………………………………………………………………………………………………………………………………….... 37 Materials and methods………………………………………………………………………………………………………………………... 39 Results……………………………………………………………………………………………………………………………………………………….... 42 Discussion……………………………………………………………………………………………………………………………………………….... 43 Acknowledgments………………………………………………………………………………………………………………………………... 45 Literature cited………………………………………………………………………………………………………………………………………... 46 Tables……………………………………………...……………………………………………………………………………………………….... 49 Figure headings………………………………………………….……………………………………………………………………….... 51 CHAPTER 4. DELINEATION OF THE OCCURRENCE, DISTRIBUTION, AND ANNUAL AVAILABILITY OF POTENTIAL HOSTS OF Phakopsora pachyrhizi IN CENTRAL AMERICA, THE CARIBBEAN, AND MEXICO…………………... 61 Abstract…………………………………………………………………………………………………………………………………………………….... 61 Introduction……………………………………………………………………………………………………………………………………………... 62 Materials and methods………………………………………………………………………………………………………………………... 63 Results and discussion………………..……………………...……………………………………………………………………………….... 65 Summary………………………………………………………………………………………………………………………………………………….... 79 Literature cited ……………………………………………………………....………………………………………………………………………... 80 List of tables…………………………………………………………………………………………………………………………….…... 90 List of figures………………….…………………………………………………………………………………………………………… 91 CHAPTER 5. GENERAL CONCLUSIONS……………………………………….... 100 Acknowledgments……………………………………………………………………………... 101 APENDICES………………………………………………………………………... 102 v ABSTRACT Role of susceptible hosts of Phakopsora pachyrhizi in the occurrence of epidemics of Asian soybean rust (ASR) in the U.S. was assessed. Phenology of kudzu (Pueraria montana var. lobata) along a ~800 km transect in the U.S. was characterized in 2003 and 2004 to assess the potential for kudzu to serve as an inoculum source for occurrence of ASR and subsequent spread to the north central soybean growing regions. Also, the occurrence, distribution, and growing periods of six potential hosts of P. pachyrhizi (including kudzu and soybean), in Central America, the Caribbean, and Mexico, were delineated. Sampling data revealed that bud break of kudzu plants in the two consecutive years of study occurred as early as April 7 from southern Louisiana (29.8 N latitude) to northern Mississippi (35.0 N latitude); kudzu green leaf area index decreased linearly with increasingly northern latitude (R2 and regression coefficient = 0.750 & –0.097, respectively, for 2003 and 0.654 & –0.384 for 2004). Further, results of modeling predicted that in southern Mississippi (31.5 N latitude), kudzu plants broke dormancy in the second and first week of March in 2003 and 2004, respectively. Modeling also showed that kudzu vines may break dormancy prior to March 1st in areas of southern and central Florida and southern Louisiana. Amount of kudzu foliage increased abruptly from April to May and June. Five out of the six hosts investigated in Central America, the Caribbean, and Mexico, were found to occur in such regions. Occurrence of selected hosts in each region was documented and maps of distribution and cultivation period schemes were generated. 1 CHAPTER 1. GENERAL INTRODUCTION Thesis organization This thesis is organized in five chapters. The first chapter is a general introduction, which includes three sections: a description of the organization of the thesis itself, a brief introduction that deals with the importance of this study, and a list of the bibliographic references cited in this introduction. The second chapter is a literature review in which I have compiled relevant topics that can help better explain the objectives and focus of this study. Information on the ecology of soybean rust, its causal agent, an update of its current global distribution, and recent findings reports in the U.S., has been included. Also, included in this chapter is some information concerning kudzu as an additional component in the pathosystem of soybean rust. A list of the references reviewed appears at the end of this chapter. The third and fourth chapters are two separate studies. The first one is an analysis of the importance of kudzu plants in the epidemiology of soybean rust in the U.S., to be submitted to the Plant Health Progress Journal. The second study is a documentation of the occurrence, distribution, and growing periods of suitable hosts of Phakopsora pachyrhizi in Central America, the Caribbean, and Mexico. The last chapter contains the general conclusions of this study and acknowledgments to institutions and people who provided assistance in