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Effects of Pythium and Cold Storage on the Survival of Southern Pine Seedlings

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Effects of Pythium and Cold Storage on the Survival of Southern Pine Seedlings Effects of Pythium and Cold Storage on the Survival of Southern Pine Seedlings by Daniel Paul Jackson A dissertation submitted to the Graduate Faculty of Auburn University in partial fulfillment of the requirements for the Degree of Doctor of Philosophy Auburn, Alabama August 9, 2010 Keywords: Pythium dimorphum, Pythium irregulare, root growth potential, root collar diameter Copyright 2010 by Daniel Paul Jackson Approved by Scott A. Enebak, Co-Chair, Professor of Forest Pathology Charles H. Gilliam, Co-chair, Professor of Horticulture David B. South, Professor of Forestry D. Joseph Eakes, Professor of Horticulture Abstract Cold storing bareroot loblolly pine (Pinus spp.) seedlings for > 1 week after lifting from October to mid-December has been associated with poor outplanting survival compared to when seedlings are lifted and stored in January. In contrast, container- grown seedling survival is not affected when stored for > 1 week during the same period. The practice of lifting bareroot seedlings can wound root systems, which pathogenic fungi, particularly Pythium spp., could use as infection sites. Once seedlings are placed in storage, the cool, moist environment may be conducive for fungal growth which could lead to seedling mortality after outplanting. The objective of this research was to evaluate bareroot and container-grown seedling survival after inoculations with Pythium dimorphum Hendrix and Campbell and Pythium irregulare Buisman and cold storage. Bareroot longleaf pine (Pinus palustris) survival decreased as a result of the Pythium inoculations but bareroot loblolly (Pinus taeda) and slash pine (Pinus elliottii) were not affected by Pythium. Container-grown seedling survival was similar to non- inoculated seedlings even after wounding root systems. When a peat-mix was packed around inoculated bareroot loblolly pine roots and used as a container media, seedling survival did not improve. This suggests that something other than antagonistic fungi in peat may improve container-grown seedling storability. As a fine feeder root pathogen, Pythium can kill the fine feeder roots that are critical for seedling establishment after outplanting, and therefore, the effects of Pythium ii on seedling root growth potential (RGP) were tested. Pythium reduced bareroot loblolly and slash pine RGP after storage, but only P. irregulare-inoculated slash pine experienced reductions in survival after outplanting. Pythium must be present in nursery soils if bareroot seedlings are infected with Pythium during fall lifting. Bareroot nursery soils were assayed to quantify Pythium populations during the fall and winter seasons. Pythium populations were variable between nurseries with more Pythium being recovered from samples taken in the fall of Year 1 and winter of Year 2. It was determined that both P. dimorphum and P. irregulare act as storage pathogens. If Pythium spp. are actively present in the soil at lifting, infect seedling roots through wounds, and grow on seedling roots in cold storage, reductions in seedling root growth potential and survival are possible. iii Acknowledgments First, I would like to thank Dr. Charles Gilliam for agreeing to work with me and Dr. Scott Enebak on this joint project. To my graduate committee, Drs. Scott Enebak, David South, Charles Gilliam, and Joseph Eakes, I thank you for being teachers, listeners, providers of numerous opportunities, and for always having an open door. I am grateful to the Southern Forest Nursery Management Cooperative for funding this research. I thank Dr. Tom Starkey for his perpetual support and for always lending an ear. To Tommy Hill, Marietjie Quicke, and Barry Brooks, thank you for all of your time and hard work, but more importantly, for your friendship. I also thank Greg Creech, Chris Marble, Rena Miller, and Patrick Jernigan for their assistance. I look forward to the life- long friendships I will have with Dr. George Matusick, David Dyson, Jay Ransom, and Ben Whitaker and will always cherish our camaraderie. I thank my parents, David and Pamela Jackson, and my in-laws, John and Rebecca Brennan, for driving long hours to Auburn for visits and for their uplifting spirits. To my wife, Missy, the sacrifices you have made are countless, and my hope is that one day I can repay you for being such a kind, loving, and patient person. To my son, Brennan, you have made the last seven months of this journey the best. This dissertation is dedicated to Dr. James Barnett, a pioneer, who contributed over 45 years to pine regeneration research and who gave me an opportunity on February 26, 2001, which changed my life forever. iv Table of Contents Abstract ............................................................................................................................... ii Acknowledgments ............................................................................................................. iv List of Tables .................................................................................................................... xii List of Figures .................................................................................................................. xvi Chapter 1-Review of Literature ...........................................................................................1 1.1. Forest Tree Nurseries in the Southern United States ......................................1 1.1.1. Lifting Practices ..............................................................................3 1.1.2. Packing and Cold Storage Practices ...............................................4 1.1.3. Cold Storage and Seedling Survival ...............................................7 1.2. Pythium in Southern Forest Tree Nurseries ..................................................11 1.2.1. Pythium in Bareroot Nurseries ......................................................11 1.2.2. Nursery Fumigation and Pythium Populations .............................13 1.2.3. Pythium in Container Nurseries ....................................................15 1.2.4. Pythium and Peat Moss Suppressiveness ......................................16 1.3. Pythium Taxonomy and Biology ....................................................................17 1.4. Pythium dimorphum ......................................................................................18 1.5. Pythium irregulare ........................................................................................20 1.6. Forest Tree Nurseries in the Pacific Northwest Region of the United States 21 1.6.1. Lifting Practices ............................................................................21 v 1.6.2. Packing and Cold/Freezer Storage Practices ................................22 1.6.3. Cold/Freezer Storage and Seedling Survival ................................24 1.7. Cold Storage and Seedling Root Growth Potential .......................................26 1.8. Central Theme of Research ...........................................................................29 1.9. Literature Cited .............................................................................................30 Chapter 2-Effects of Pythium and Cold Storage on Longleaf, Loblolly, Slash, and Shortleaf Pine Survival ....................................................................................................40 2.1. Abstract .........................................................................................................40 2.2. Introduction ....................................................................................................41 2.3. Materials and Methods ..................................................................................43 2.3.1. Pythium Inoculum .........................................................................43 2.3.2. Seedling Inoculations ....................................................................44 2.3.3. Seedling Survival ..........................................................................47 2.3.4. Pythium Populations .....................................................................47 2.3.5. Statistical Analyses .......................................................................49 2.4. Results .............................................................................................................49 2.4.1. Bareroot Seedlings ........................................................................49 2.4.1.1. Longleaf Pine ..............................................................49 2.4.1.2. Loblolly Pine ...............................................................50 2.4.1.3. Slash Pine ....................................................................55 2.4.2. Container-grown Seedlings ...........................................................58 2.4.2.1. Longleaf Pine ..............................................................58 2.4.2.2. Loblolly, Slash, and Shortleaf Pine.............................58 vi 2.5. Discussion .......................................................................................................72 2.5.1. Seedling Survival ..........................................................................72 2.5.1.1. Bareroot Seedlings ......................................................72 2.5.1.2. Container-grown Seedlings .........................................73 2.5.2. Pythium Populations .....................................................................74 2.5.2.1. Bareroot Seedlings ......................................................74 2.5.2.2. Container-grown
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