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The Pennsylvania State University The Pennsylvania State University The Graduate School Department of Plant Pathology and Environmental Microbiology CHARACTERIZATION OF Pythium and Phytopythium SPECIES FREQUENTLY FOUND IN IRRIGATION WATER A Thesis in Plant Pathology by Carla E. Lanze © 2015 Carla E. Lanze Submitted in Partial Fulfillment of the Requirement for the Degree of Master of Science August 2015 ii The thesis of Carla E. Lanze was reviewed and approved* by the following Gary W. Moorman Professor of Plant Pathology Thesis Advisor David M. Geiser Professor of Plant Pathology Interim Head of the Department of Plant Pathology and Environmental Microbiology Beth K. Gugino Associate Professor of Plant Pathology Todd C. LaJeunesse Associate Professor of Biology *Signatures are on file in the Graduate School iii ABSTRACT Some Pythium and Phytopythium species are problematic greenhouse crop pathogens. This project aimed to determine if pathogenic Pythium species are harbored in greenhouse recycled irrigation water tanks and to determine the ecology of the Pythium species found in these tanks. In previous research, an extensive water survey was performed on the recycled irrigation water tanks of two commercial greenhouses in Pennsylvania that experience frequent poinsettia crop loss due to Pythium aphanidermatum. In that work, only a preliminary identification of the baited species was made. Here, detailed analyses of the isolates were conducted. The Pythium and Phytopythium species recovered during the survey by baiting the water were identified and assessed for pathogenicity in lab and greenhouse experiments. The Pythium species found during the tank surveys were: a species genetically very similar to P. sp. nov. OOMYA1702-08 in Clade B2, two distinct species of unknown identity in Clade E2, P. coloratum or one of the very closely related species such as P. diclinum, P. middletonii, an unknown species in Clade B2, an isolate somewhat similar to P. sp. nov. OOMYA1646-08 (E2), P. rostratifingens, and an unknown species in Clade A. In addition, three Phytopythium species were found: Phytopythium litorale, Ph. helicoides, and Ph. chamaehyphon. Many of these species are considered weak pathogens and some display resistance to the Oomycete fungicide, mefenoxam. Of the baited isolates, seven expressed resistance (Ph. helicoides, Clade E2-2 unknown, P. middletonii, P. sp. nov. OOMYA1646-08 (E2),) with three displaying high resistance (P. coloratum, P. rostratifingens, Clade A unknown). Seven expressed sensitivity (Ph. helicoides, Clade B2 unknown, P. sp. nov. OOMYA1646-08 (E2), Ph. chamaehyphon) with three displaying high sensitivity (Clade E2-1 unknown, P. coloratum, Clade E2-2 unknown). In a lab experiment, using Pelargonium X hortorum seeds germinated on moistened filter paper, some of the baited isolates were pathogenic. However in another test using small pots containing pasteurized, peat-based soilless potting mix, none of the baited isolates were pathogenic on geranium seedlings. It was assessed whether or not these isolates that were frequently obtained by baiting interfere with known pathogenic Pythium species, P. aphanidermatum, P. irregulare, and P. cryptoirregulare, in disease development. Some of the isolates slowed or promoted plant disease in the lab test using geranium seedlings on moistened filter paper, but these results were unable to be reproduced in the greenhouse experiments under more natural production conditions. At the end of the greenhouse experiments, root sections were plated in order to iv recover isolates. It was found that in the co-inoculated plants, P. irregulare and P. cryptoirregulare were almost always the only species recovered from the roots. The baited isolates were still recovered from the roots in the control plants. Lastly, a simulation of the greenhouse ebb and flood irrigation system was set up to determine if P. aphanidermatum can coexist with representatives of the frequently baited isolates in recycled irrigation water tanks. P. aphanidermatum was not recovered from any of the tanks or on the roots of plants the tanks watered. We conclude that there is an array of Pythium and Phytopythium species that reside in greenhouse irrigation systems, and that P. aphanidermatum is not one of those species. Thus, treating irrigation water with chlorine or other chemicals to remove Pythium spp. may not be necessary in greenhouses where potted plants are irrigated with recycled water. We also conclude that the highly virulent species Pythium irregulare and Pythium cryptoirregulare have attributes that allow them to dominate the niche of plant roots over those species frequently found in the irrigation water. v TABLE OF CONTENTS List of Tables……………………………………………………………………………..…….vii List of Figures………………………………………………………………………………….viii Acknowledgements…………………………………………………………………………...…ix Chapter 1. LITERATURE REVIEW…………………………………………….………………1 The Genera Pythium and Phytopythium……………………………….…………...………....….1 Pythium in Greenhouses………………………………………………………………………….2 Pythium Evolution & Ecology………………………………...………………………………… 6 Objectives……………………………………………………………………………………….10 Literature cited……………………………………………………………....……………...…..11 Chapter 2. IDENTIFICATION AND CHARACTERIZATION OF Pythium AND Phytopythium SPECIES IN TWO COMMERCIAL GREENHOUSE RECYCLING IRRIGATION WATER SYSTEMS……………………………………………………..…......20 Abstract……….…………………………………………………………………………...……20 Introduction………………………………………………………………………………...…...20 Materials and Methods……………………………………………………………………….....23 Baiting and Biological Characterization…………………………………………..…....23 Mefenoxam Resistance………………………………………………………………....24 Genetic characterization……………………………………………………………..….25 Results………………………………………………………………………………………......26 Discussion………………………………………………………………...……………....….....47 Acknowledgements………………………………………………………………...…………...49 Literature cited……………………………………………………….……………...………….50 Chapter 3. PATHOGENICITY OF THE SPECIES OF Pythium AND Phytopythium FREQUENTLY FOUND IN RECYCLED IRRIGATION WATER AND THEIR INTERACTIONS WITH Pythium aphanidermatum, P. irregulare, AND P. cryptoirregulare………………………………………………………………………….…..56 Abstract…………………………………………………………………………………..……..56 Introduction…………………………………………………………….……………………….56 Materials and Methods……………………………………………………………………...…..58 Results………………………………………………………………………………………......62 Discussion………………………………………………………………………………..…..…65 Acknowledgements….…………………………………………………………………...……..67 Literature cited…….……………………………………………………………………...….…68 Chapter 4. AQUATIC SURVIVAL OF Pythium aphanidermatum, Phytopythium helicoides AND Pythium coloratum……………………………….....................71 Abstract……..………………………………………………………………………………..…71 vi Introduction……...…………………………………………………………………………...…71 Materials and Methods……………………………………………………………………….....72 Results………………………………………………………………………………………......74 Discussion…………………………………………………………………………………........76 Acknowledgements…………………………………………………………………………......77 Literature cited……………………………………………………………………………….....78 CONCLUSION……………………………………………………………………………...….80 Appendix: Supplementary Data……………………………………………………….………..83 vii LIST OF TABLES Table 2-1. The cardinal temperatures of the baited isolates, their daily growth rates, and colony morphology on PCA....................................................................................................................39 Table 2-2. The means in µm of structures of baited Pythium species. …………………………45 Table 2-3. Results of the poison plate assay. …………………………………………………..46 Table 3-1. Pathogenicity on geranium seedlings grown on filter paper moistened with soluble fertilizer and co-inoculation results.……………………………………..……………………...64 Table 3-2. Combined results of the root isolations from the co-inoculation experiments…..….64 Table 4-1. Experimental setup for ebb and flow experiment………………………………..….73 Table 4-2. The number of hours the tanks had water temperatures between 25° and 30° C.………………………………………………………………………………………………..75 Table 4-3. Isolates from baits during the experiment……………………………………...........75 Table A-1. Initial morphological observations of the isolates. ………………………………...86 Table A-2. A summary of the Pythium isolates baited from greenhouse irrigation tanks……...91 Table A-3. The cardinal temperatures of the isolates, mean daily growth rates at 25C on PCA, and colony morphology on PCA……………………………………….….…..92 Table A-4. Full results of the poison plate assay…………………………………………....…..94 Table A-5. A list of the isolates used for detailed microscopic identification………………….97 Table A-6. The average water temperature during the week the isolates were initially baited from the two greenhouses, compared to their cardinal temperatures…………………..........….98 Table A-7. Average water temperature (°C) for 7 day periods ending on the sampling date in two commercial greenhouses………………………………………………………………...…99 Table A-8. Isolate pathogenicity and co-inoculating results……………...……..…………….100 Table A-9. The representative isolates used in the greenhouse pathogenicity and co-inoculation tests……………………………………………....………………………………….…………101 Table A-10. A list of the isolates used for the lab soil pathogenicity tests…………………....103 Table A-11. Average weekly tank temperatures in the tank isolate survival tests………..…...104 viii LIST OF FIGURES Figure 2-1. A maximum likelihood analysis concatenated gene tree of the ITS and COII regions with 1000 bootstraps……………………………..……………………..33 Figure 2-2. A new species analysis of the isolates of unknown identity in Clade E2…….....…34 Figure 2-3. A portion of the new species analysis for the Clade B2 unknown
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