Downy Mildew Caused by Hyaloperonospora (Peronospora) spp. on Wild Rocket (Diplotaxis tenuifolia) and Other Crops from Brassicaceae Family By Jana Johansen Hladilová In Partial Fulfilment of the Requirements for the Degree of Master of Science Supervised by Professor Anne Marte Tronsmo Arne Hermansen Berit Nordskog Norwegian University of Life Sciences Department of Plant and Environmental Sciences December, 2010 Acknowledgements I thank the Bioforsk who made this master thesis possible by covering all the expenses of the experiments. I extend my deepest gratitude to Professor Anne Marte Tronsmo. I thank Arne Hermansen and Berit Nordskog for help with the experiments, necessary technical instructions and for involvement in their work agenda related to the project. I thank Professor Anne Marte Tronsmo and Berit Nordskog for the comments before the submission of my thesis. I thank all my supervisors for their enthusiasm and their advice to the project. I thank Ingrid Færgestad Bugge for the friendly and helpful attitude regarding the administration of my permission. I thank Elisa Gauslå for help with the host specificity experiments. It was nice to have a friend. I thank Vinh Hong Le for the advice about the solar experiment. I thank my family for their support and encouragement. I specially thank my loving husband Øivind Stokkenes Johansen for all the help with our daughters, Elise and Klara. Also I would like to thank my father Assoc. Prof. Jindřich Hladil for the geological advice. The time spend on work on my thesis was a big part of my studies at Ås and my first years here in Norway. It was an experience to be known with the norwegian society and working environment. Table of Contents BACKGROUND..............................................................................................................................1 AIMS OF THESIS ...........................................................................................................................2 LITERATURE REVIEW....................................................................................................................3 Brassicaceae Family.................................................................................................................3 Cultivated Rocket Salad, Wild Rocket.................................................................................3 Downy Mildew........................................................................................................................5 Causal Organism.................................................................................................................5 Disease Cycle......................................................................................................................6 Symptoms..........................................................................................................................7 Taxonomy...........................................................................................................................8 Host Specificity.................................................................................................................10 Host-pathogen Interaction...............................................................................................10 Epidemiology....................................................................................................................11 Control.............................................................................................................................11 HOST SUSCEPTIBILITY.................................................................................................................12 INTRODUCTION ....................................................................................................................12 METHODS AND MATERIAL....................................................................................................12 Part 1................................................................................................................................13 Cultivation of Seedlings ..............................................................................................13 Source of Primary Inoculum........................................................................................14 Spore Harvesting.........................................................................................................15 Inoculation on Seedlings and Promotion of Asexual Sporulation................................16 Disease Assessment ...................................................................................................16 Part 2................................................................................................................................17 Cultivation of Seedlings ..............................................................................................17 Source of Primary Inoculum........................................................................................18 Treatment of Isolate....................................................................................................20 Spore Harvesting.........................................................................................................20 Establishment of Sufficient Amount of Inoculum........................................................20 Inoculation on COMPLETE SET ...................................................................................21 Disease Assessment....................................................................................................22 RESULTS.................................................................................................................................24 Part 1................................................................................................................................24 Part 2................................................................................................................................24 COMPLETE Sets...........................................................................................................24 D. tenuifolia Isolates...............................................................................................24 Swede Isotates.......................................................................................................27 Broccoli isolates.....................................................................................................29 Other Infected Sets.....................................................................................................34 D.tenuifolia Isolates...............................................................................................35 Swede Isolates .......................................................................................................35 Broccoli Isolates.....................................................................................................35 Isolates of Weed Host Plant..................................................................................36 Comprehensive Results of Sets Infected with Isolates from Host Plant D.tenuifolia, Swede and Broccoli .........................................................................................................36 DISCUSSION...........................................................................................................................38 Source of Primary Inoculum.............................................................................................38 Spore Concentration........................................................................................................38 Mean Leaf Disease Severity, Plant Disease Incidence......................................................38 Host Specificity.................................................................................................................39 SURVIVAL OF CONIDIA OF Hyaloperonospora (Peronospora) spp. IN AIR..................................42 INTRODUCTION.....................................................................................................................42 METHODS AND MATERIAL....................................................................................................42 Cultivating Cultures of Wild Rocket and Swede...............................................................42 Isolates.............................................................................................................................42 Inoculation on Seedlings..................................................................................................42 Promotion of Asexual Sporulation...................................................................................43 Placement of Spores on Membrane Paper.......................................................................43 Solar Exposure..................................................................................................................43 Treatment and Incubation of Exposed Spores.................................................................44 Assessment of Viability of Spores.....................................................................................44 RESULTS ................................................................................................................................45 First counting ...................................................................................................................45 Second counting ..............................................................................................................51