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Microbial Suppression of Pythium Root Rot in Soilless Systems

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Microbial Suppression of Pythium Root Rot in Soilless Systems Microbial Suppression of Pythium Root Rot in Soilless Systems Cora McGehee B.S. Louisiana State University, 2015 A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science At the University of Connecticut 2018 Copyright by Cora Shields McGehee 2018 ii APPROVAL PAGE Master Thesis Microbial Suppression of Pythium Root Rot in Soilless Systems Presented by Cora Shields McGehee, B.S. Major Advisor_________________________________________________________________ Rosa E. Raudales Associate Advisor______________________________________________________________ Wade H. Elmer Associate Advisor_______________________________________________________________ Richard J. McAvoy University of Connecticut 2018 iii Acknowledgements I am beyond grateful to my major advisor Dr. Rosa Raudales for her hard work and dedication to the lab and innovative research projects. Her guidance and patience has made me into a stronger researcher and diligent worker. I also want to thank the other members of my committee Dr. Wade Elmer and Dr. Richard McAvoy for their time and generous advice. I want to thank Frederick Pettit, Shelley Durocher, and Ronald Brine for their assistance in the various greenhouse projects conducted. Thank you Margery Daughtrey for supplying isolates for experiments. Special thanks to Juan Cabrera, Sohan Aziz, Steve Olenski, Joy Tosakoon, and Carla Caballero for giving your time to help with experiments. Lastly a thank you to the office staff, Christine Strand and Nicole Gabelman for their assistance and kindness. Special thanks to the U.S. Department of Agriculture via the Connecticut Department of Agriculture Specialty Crop Block Grant # AG151260 for its support and funding of this work. Thank you to friends and family who supported me over the phone during this intense intellectual pursuit. iv Table of Contents Page Abstract ........................................................................................................................................ vii Chapter 1 ....................................................................................................................................... 1 Introduction ............................................................................................................................... 1 Literature Cited ......................................................................................................................... 6 Chapter 2 ....................................................................................................................................... 9 Characterization of Pythium spp. Isolates Obtained in Commercial Greenhouses ............ 9 Abstract ...................................................................................................................................... 9 Introduction ............................................................................................................................. 10 Materials and Methods ........................................................................................................... 12 Results ...................................................................................................................................... 17 Discussion ................................................................................................................................. 20 Literature Cited ....................................................................................................................... 23 Figures ...................................................................................................................................... 28 Tables........................................................................................................................................ 37 Annex ........................................................................................................................................ 43 Chapter 3 ..................................................................................................................................... 47 Efficacy of Microbial Biofungicides on Suppressing Pythium Root Rot on Hydroponic Lettuce (Lactuca sativa L.) ...................................................................................................... 47 Abstract .................................................................................................................................... 47 Introduction ............................................................................................................................. 48 Materials and Methods ........................................................................................................... 49 Results ...................................................................................................................................... 53 Discussion ................................................................................................................................. 54 Conclusion ................................................................................................................................ 56 Literature Cited ....................................................................................................................... 57 Figures ...................................................................................................................................... 61 Tables........................................................................................................................................ 64 Chapter 4 ..................................................................................................................................... 70 Efficacy of Microbial Biofungicides against Root Rot and Damping-off of Microgreens caused by Pythium spp. ........................................................................................................... 70 Abstract .................................................................................................................................... 70 Introduction ............................................................................................................................. 71 v Materials and Methods ........................................................................................................... 72 Results ...................................................................................................................................... 76 Discussion ................................................................................................................................. 78 Conclusion ................................................................................................................................ 78 Literature Cited ....................................................................................................................... 81 Figures ...................................................................................................................................... 85 Tables........................................................................................................................................ 88 Chapter 5 ..................................................................................................................................... 91 Conclusions .............................................................................................................................. 91 vi Abstract Pythium spp. are the causal agents of Pythium root rot and damping-off on leafy vegetables in hydroponic systems. Infected plants have low quality and biomass resulting in significant losses to farmers. In the US, synthetic fungicides are not registered for direct application in hydroponic solutions and only a few are registered for application on edible crops in greenhouses. The efficacy of microbial biofungicides depends on the plants and environmental conditions that are conducive for the survival and activity of the microbes. The objectives of this project were to (1) isolate pathogenic Pythium spp. from commercial greenhouses in the northeastern US, (2) evaluate if recirculated nutrient solutions have the potential to inhibit Pythium spp., and (3) evaluate the efficacy of microbial biofungicides on the disease incidence and severity of Pythium root rot in hydroponic lettuce (Lactuca sativa), arugula (Eruca sativa), kale (Brassica oleracea var. sabellica), radish (Raphanus raphanistrum subsp. sativus), and mustard (Brassica juncea) microgreens in hydroponic systems. We obtained nine isolates of P. aphanidermatum, P. dissotocum, and P. graminicola. The isolates were identified using standard morphological identification keys and confirmed with sequencing of the internal transcribed spacer (ITS) regions 1 and 4 of the ribosomal DNA gene. This is the first report of P. dissotocum on lettuce in Connecticut, and P. aphanidermatum on mustard, mizuna, Swiss chard, and wheatgrass in New York. In a second experiment, recirculated nutrient solution from commercial farms inhibited Pythium spp. growth in vitro. In a third experiment, we tested the efficacy of the microbial biofungicides Companion® (Bacillus subtilis GB03), Triathlon BA® (Bacillus amyloliquefaciens D747), RootShield® (Trichorderma harzianum KRL-AG2), RootShield Plus® (Trichoderma harzianum KRL-AG2 and Trichoderma virens G-41), Cease® (Bacillus subtilis QST 713), and Actinovate® (Streptomyces lydicus WYEC 108) on Pythium
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