ABSTRACT BECKER, LINDSEY ELIZABETH. Increased Flower Production and Plant Weight of Calibrachoa x hybrida by the Soil Fungus Mortierella elongata. (Under the direction of Dr. Marc A. Cubeta). Calibrachoa (Calibrachoa x hybrida), is a flowering ornamental plant, commonly known as a mini-petunia or million bells and is rapidly gaining popularity as a flowering bedding and hanging plant. It has a range of desirable horticultural characteristics, including attractive flowers, range of flower colors, drought tolerance, and plant habit. The saprobic fungus Mortierella elongata isolated as an endophyte from Populus deltoides (eastern cottonwood) roots has been shown to increase seedling growth of corn, red oak and tomato in pasteurized sand and untreated field soil. In this context, we conducted two greenhouse experiments in 2017 to evaluate the effect of potting media amendments of millet colonized with M. elongata at 1 and 2% (v/v) on plant growth of Calibrachoa cv. ‘Kabloom Deep Blue’ rooted cuttings. Plants were assessed weekly for flower production and at 86 days post inoculation for above/below ground dry weight. M. elongata isolate 624- significantly increased the number of flowers produced for inoculum volumes 1 and 2% over a period of 3- 5 weeks for both experiments and increased above and belowground plant dry weight during experiment 1. Our findings suggest that M. elongata 624- consistently promotes flower production of Calibrachoa. Calibrachoa, valued for its aesthetic qualities, requires constant surveillance for disease symptoms. Susceptibility of Calibrachoa to the soilborne fungal pathogen Thielaviopsis basicola (causal agent of black root rot) is informally well-known but has not been the subject of comprehensive investigation. When Calibrachoa are infected with T. basicola, they exhibit stunting and chlorosis, which makes them unsuitable for market. In two greenhouse experiments conducted in 2017, we screened seven commercially available Calibrachoa cultivars for resistance to a virulent isolate of T. basicola. In this study, we developed an experimental protocol and root rating scale for evaluating severity of black root rot disease on Calibrachoa plants. Calibrachoa cultivars exhibited varying susceptibility to the pathogen. Two cultivars, ‘Minifamous Compact Hot Pink’ and ‘Deep Blue Kabloom’ had significantly higher dry root weight and lower disease severity ratings compared to ‘Callie Scarlet’. These results suggest that ‘Minifamous Compact Hot Pink’ and ‘Deep Blue Kabloom’ may exhibit partial resistance to T. basicola. Our results highlight the need for continued evaluation of Calibrachoa cultivars to T. basicola, which may aid breeders in identifying sources of resistance to black root rot disease in Calibrachoa. © Copyright 2017 Lindsey Elizabeth Becker All Rights Reserved Increased Flower Production and Plant Weight of Calibrachoa x hybrida by the Soil Fungus Mortierella elongata by Lindsey Elizabeth Becker A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science Plant Pathology Raleigh, North Carolina 2017 APPROVED BY: _______________________________ _______________________________ Dr. Shuijin Hu Dr. Howard D. Shew _______________________________ Dr. Marc A. Cubeta Committee Chair DEDICATION This manuscript is dedicated to my parents, Don and Polly Becker, my grandparents, Marguerite and Fitzhugh Turner, and to my partner in love, life, and scientific pursuit of excellence, Camilo Humberto Parada Rojas. ii BIOGRAPHY Lindsey Elizabeth Becker was born on May 21st, 1988 in Durham, North Carolina. She received her bachelor of art (B.A.) in biological sciences at The College of Wooster in Wooster, Ohio. While pursuing her bachelors, Ms. Becker studied the spatial/temporal destruction of Ash trees (Fraxinus spp.) by the emerald ash borer in southeastern Michigan for her senior thesis. Post-graduation, Ms. Becker worked in the labs of Dr. Jim Clark and Dr. Rytas Vilgalys at Duke University for four years, acting as lead technician on a project investigating the fungal endophytic community of tree seedlings commonly found in forests in the Southeast US. She was mentored by Dr. Soledad Benitez Ponce during this time, who introduced Ms. Becker to the field of plant pathology. This experience led Ms. Becker to pursue a Master’s of Science at NC State University in plant pathology under the guidance of Dr. Marc Cubeta. Ms. Becker’s research focuses on understanding the effects of the soil fungi Mortierella elongata on the ornamental plant Calibrachoa, and also detailing the susceptibility of Calibrachoa cultivars to the common soilborne fungal pathogen Thielaviopsis basicola, causual agent of black root rot. Ms. Becker has presented the results from this thesis in 2017 at the annual meeting of the Mycological Society of America in Athens, GA. She is currently serving as president of the Plant Pathology Graduate Student Association and has served as the representative of the PPGSA for the University Graduate Student Association. iii ACKNOWLEDGMENTS I would first like to thank Dr. Brigid Hogan, for offering me a job in her lab when I was still in high school. Thank you for being so supportive of me every step of the way, even when my interests shifted to fungi and ecology rather than epithelial stem cells. Your encouragement strengthened my resolve to pursue what I loved. I would like to thank my advisor, Dr. Marc Cubeta, for encouraging me to work on a project with many unknowns. I highly value the wisdom you impart during casual chats in the lab and long car rides. Your unconventional thinking challenges me to approach everything with an open mind. I would also like to thank you for giving me the opportunity to work on this project and to be in your lab. Many thanks to my committee members, Drs. Shuijin Hu and Dave Shew, for their advice and input throughout the course of this project. I would also like to thank Dr. Soledad Benitez Ponce for encouraging me to combine my love of plants and fungi via the world of plant pathology. Dr. Rytas Vilgalys practically adopted me into his mycology lab when I was working on a fungal endophyte project, and kindly gave me opportunities to attend MASMC and connect with others in mycology. The Vilgalys lab ethos of community, support, and love was always inviting and inclusive, and I continue to appreciate that to this day. To my fellow graduate students in the plant pathology program at NCSU, thank you for being an inspiring and wonderful group of people to work with. I would like to also thank my parents for their continuous love and support. They have always emphasized the importance of self-care in relation to enjoying work. I thank my iv mother for long walks and for always being available to listen. I would also like to thank my father for all of the long bike rides that never failed to make me feel better. Last, but certainly not least, a huge thank you to Camilo Parada for all of your love, encouragement, support, numerous ice cream cones at the library, and your thorough reviews of this thesis. v TABLE OF CONTENTS LIST OF TABLES…………………………………………………………………………viii LIST OF FIGURES………………………………………………………………………....ix CHAPTER I. Literature Review…………………………………………………………....1 Calibrachoa…………………………………………………………………………..1 Calibrachoa and micronutrients…………………………………………………... 3 Common soilborne fungal pathogens of Calibrachoa………………...…….…......4 Thielaviopsis basicola…………………………….............................................……..4 Black root rot symptoms on Calibrachoa…..........................................................…5 Management of black root rot disease.......................................................................6 Cultural management…..............................................................................................6 Chemical management…............................................................................................6 Biological management…............................................................................................7 Host resistance…......................................................................................................…7 Fungal endophytes…...................................................................................................8 Plant growth promotion by fungal endophytes…...................................................10 Mechanisms of plant growth promotion by fungal endophytes…........................11 Mortierella elongata…................................................................................................11 Ecology of M. elongata…...........................................................................................12 Research hypotheses and objectives….....................................................................13 LITERATURE CITED….........................................................................................14 vi CHAPTER II. Increased flower production and plant weight of Calibrachoa x hybrida by the soil fungus Mortierella elongata…………………………………........….................23 ABSTRACT………………………………………………………………........……23 INTRODUCTION…………………………………………………………….........25 MATERIALS AND METHODS..............................................................................28 RESULTS……………………………………………………………………….......31 DISCUSSION…………………………………………………………………….....36 ACKNOWLEDGMENTS……………………………………………………….…41 LITERATURE CITED………………………………………………………….…42 CHAPTER III. Susceptibility of Calibrachoa