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CANOPY and LEAF GAS EXCHANGE ACCOMPANYING PYTHIUM ROOT ROT of LETTUCE and CHRYSANTHEMUM a Thesis Presented to the Faculty Of

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CANOPY and LEAF GAS EXCHANGE ACCOMPANYING PYTHIUM ROOT ROT of LETTUCE and CHRYSANTHEMUM a Thesis Presented to the Faculty Of CANOPY AND LEAF GAS EXCHANGE ACCOMPANYING PYTHIUM ROOT ROT OF LETTUCE AND CHRYSANTHEMUM A Thesis Presented to The Faculty of Graduate Studies of The University of Guelph In partial ful filment of requirements for the degree of Master of Science January, 200 1 Q Melanie Beth Johnstone, 200 1 National Library Bibliothèque nationale 191 of Canada du Canada Acquisitions and Acquisitions et Bibliographic Services seivices bibliographiques 395 Wellington Street 395, me Wellington Ottawa ON KIA ON4 Ottawa ON K 1A ON4 Canada Canada The author has granted a non- L'auteur a accordé une licence non exclusive licence dowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or seil reproduire, prêter, distribuer ou copies of this thesis in rnicroform, vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/film, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substanhal extracts fiom it Ni la thèse ni des extraits substantiels may be printed or othenvise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. ABSTRACT CAKOPY AND LEAF GAS EXCHANGE ACCOMPANYING PYTHIUMROOT ROT OF LETTUCE AND CHRYSANTHEMUM Melanie Beth Johnstone Advisors: University of Guelph, 2000 Professor B. Grodzinski Professor J.C. Sutton The first charactenzation of host carbon assimilation in response to Pythium infection is described. Hydroponic lettuce (Lactuca sativa L. cv. Bella Green) inoculated with Pjtfhitrw dissofoctmexperienced 3 MO% growth inhibition, amibuteci to decreased lea f and whole plant photosynthesis. Leaf gas exchange and transpiration was significantly reduced as early as 7 days afler inoculation, several days in advance of visible foliar symproms. P. aphanidermarirm was mildly pathogenic in hydroponic chrysanthemum (Chrysanthemum nzori/oliurn L. cv. Fina), exhibiting reduced whole plant photosynthesis only late in the gowth cycle. Altentions in gas exchange may be useful in nondestructive, objective diagnosis of plant disease, a critical step in pathogen control in recirculating nutrient solutions. W irradiation of nutrient solutions was studied as a potential rnethod of pathogen inactivation; however, copper and zinc toxicity even with inacfivated lamps confounded evaluations. It is premature to recommend W as a remediation technology for recirculating nutrient solutions in commercial greenhouses. My sincere thanks are extended to my supervison, Drs. Bernard Grodzinski and John Sutton, for their support and guidance throughout this study. 1 would also like to acknowledge DE. Michael Dixon and J. Chris Hall, members of my advisory committee, and Drs. John Proctor and M. Jim Tsujita, the Chair and extemal representative, respectively, of the examination committee, for their involvement and critical suggestions for the irnprovement of this manuscript. I wish to express great appreciation to Dr. Hai Yu, Yaping Zheng, Dr. Weizhong Lu, and Nathan Owen-Going for P'ium inoculum preparation in this collaborative project. Bridging the gap between physiology and pathology would not have been possible without their contributions. 1 would like to thank George Lin, Rodger Tschanz, Luke Lairson, Carmrn Tse. and Emily Binnendyk for their invaluable assistance in maintenance of plant materials and hydroponic systems. 1 am extremely grateful to Geoffiey Cloutier for statistical consultations and programming support in S-Plus. This man knowç regression analysis like no other. Financial assistance From the Centre for Research in Earth and Space Technologies (CRESTech), Flowers Canada (Ont.) Ltd., CanAdapt, Natural Sciences and Engineering Research Council (NSERC), Ontario Ministry of Agriculture, Food, and Rural Affairs (OMAFRA), Ontario Greenhouse Vegetable Producers Marketing Board, and Trojan Technologies, Inc., in support of this project is most gratefully achowledged. 1 would also like to thank Rob Hansen of Erieview Acres Ltd. for providing chrysanthemum cumngs. Lastly I wish to thank my family and fiends for their emotional support and encouragement, especially Ryan Ramsey and Jeff Riggs for keepin' it real, my sistas in crime in the Bw.r community, and my parents, Bill and Sue Johnstone, whose lifelong encouragement is much appreciated. TABLE OF CONTENTS ACKYOWLEDGEMENTS ................................................................................................ i ... TABLE OF CONTENTS ................................................................................................... 111 .. LIST OF TABLES ............................................................................................................. vil ... LIST OF FIGURES ............................ ,........................................................................... v111 LIST OF DEFINED TERMS AiD ABBREVIATIONS ..................................................x CHAPTER 1: Introduction and Literature Review Chapter introduction ................... .. ......................................................................... 1 P~thiminfection ........................ ................................................................................ 3 Host Responses to Root infection 1. Cellular responses within the mot zone of host plants ............................. 5 2. Metabolic responses of the whoie plant ...................................................... 7 i. infection by fithium ........................................................................ 8 ii. Infection by other mot pathogens ................................................. 9 Root Rot Epidemics in Recirculating Hydroponics .................................................. 1 1 Emerging Technologies for Pathogen Control in Commercial Hydroponic Systems ................................................................................................. 14 CHAPTER 2: Photosynthesis and Plant Productivity of Lettuce (Lacruca sativa L. cv. Bella Green) Following Infection by Pythium dissotocum Chapter Introduction............................................................................................ 18 Materials and Methods ............................................................................................. 20 Experimental Results influence of PpLium dissotoaim on growth of lettuce ................................ 27 Whole plant gas exchange and carbon accumulation ...................................27 Influence of irradiance on whole plant NCER ............................................. 30 Influence of CO2concentration on whole plant NCER ................................ 30 Leaf chlorophyll content.............................................................................. 33 influence of irndiance on leaf gas exchange.................................................. 33 Influence of stage of host maturity on leaf gas exchange and water reIations ................ .......................................................................... 36 Influence of inoculum density on seventy of disease effects...................... 39 Specific leaf area ...................................................................................... .A2 Discussion .................................................................................. 4.c Conclusion .............................................................................................................. 56 CHAPTER 3: Photosynthesis and Plant Productivity of Chrysanthemum (Chrysa~ttlremummorifoliurn L .cv Fina) Following Infection by Pythium aph art idermatum Chapter Introduction................................................................................................ 58 Materials and Methods ....................,.,. ..................................................................... 60 Experimental Results Influence ofPythium aphanidenncltum on growth ofchrysanthemum......... 64 Whole plant gas exchange and carbon accumulation ................................. 64 Influence of Pyfhium inoculation on leaf physiology of plants . in smgle pot culture.......................................................................... 68 Effect of Pythi~trninoculation on NFT-groown chrysanthemum................. 68 Root hydraulic conductance.. .. ... ... ...... ... .. .. ... ..... .. .. .. .. .. .. .. .. .. ... .. .68 Discussion.. ... .......... ............ ... ..... .... .... .. ... .. .. .. .. ... ... ... .. .. ... ...... .. .. ... 72 Conclusion ....... ............................................ ............ ... ................................... .. ........76 CHAPTER 4: Use of Ultraviolet Irradiation of Recirculating Hydroponic Solution in Trertment of Pythiurn Root Rot Chapter Introduction ........................................................ ........ .............. ............. .. ... 78 Materials and Methods .......................... .................................................................. 80 Experirnental Results Influence of concurrent W exposure and Pythiurn inoculation on vegetative growth of chrysanthemum, Experirnent 1.................... 85 Elernental analysis of non-inoculated plants grown in W-treated nutrient solution.....,.......... .... .. ....... .......... ....................................... ... 85 Influence of Pythium inoculation on physiological parameters in plants exposed
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