Host Preference of Pratylenchus Neglectus to Major Crops of the Prairie Provinces of Canada
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Host Preference of Pratylenchus neglectus to Major Crops of the Prairie Provinces of Canada By Priscillar Wenyika A thesis submitted to the Faculty of Graduate Studies of The University of Manitoba In partial fulfilment of the requirements of the degree of Master of Science Department of Soil Science University of Manitoba Winnipeg, Manitoba, Canada Copyright © 2019 ABSTRACT Wenyika Priscillar, M.Sc., The University of Manitoba, November 2019. Host Preference of Pratylenchus spp. to Major Crops Grown in the Prairie Provinces of Canada. Advisor: Dr. M. Tenuta. Root lesion nematodes of the genus Pratylenchus Filipjev, 1936 are pests of economic importance worldwide. Pratylenchus spp. have recently been identified in soils from commercial fields in the Canadian Prairie Provinces, and there is a lack of knowledge about the host preferences of these nematodes. This research was conducted to determine: a) the crop hosts preferred by the Pratylenchus spp., b) the effects of selected pulse and non-pulse crops mainly grown in the Canadian Prairies in building-up densities of the nematode under growth chamber conditions, c) the effect of the nematode and population density over several crop growth cycles on performance of the plants, and d) the species identity of the Pratylenchus spp. Host suitability to Pratylenchus spp. was evaluated on the most widely grown varieties of selected pulse and non-pulse crops available in Canadian Prairies including canola, chickpea, lentil, pinto bean, soybean, Canada Western Red Spring Wheat, and yellow pea. Host status was assessed using the reproductive factor (Rf = final/ initial density) and plant growth parameters (plant height, above-ground, and root biomass) were measured at the end of each cycle. Nematodes recovered from the test soils and roots of host crops were identified using morphological identification and molecular assays. The suitable hosts for Pratylenchus (Rf >1) were canola, chickpea, pinto bean, soybean, and spring wheat. Soybean was the most preferred host for these nematodes with a mean above the threshold level for Pratylenchus spp. (>1000 nematodes per kg-1 of soil) in the final cycle. The population of Pratylenchus spp. in pots planted to canola, chickpea, pinto bean, soybean, and wheat significantly increased across the three growth cycles. Lentil was a poor host and yellow pea was a non-host for Pratylenchus spp. High densities of Pratylenchus reduced plant height, above-ground and root biomasses of canola, lentil, pinto bean, spring wheat, and yellow pea. Plant height and biomass of chickpea and soybean were not reduced by increasing Pratylenchus densities. The Pratylenchus spp. was identified as P. neglectus using morphometric characters, PCR with species-specific primers and DNA sequencing. Most of the crops mainly grown in the Canadian Prairies are hosts for P. neglectus. ii ACKNOWLEDGEMENTS For this work to come together, it took several hands from a lot of helpful people that surround me. I am profoundly grateful to my main supervisor, Dr. M. Tenuta for his motivation, immense knowledge and valuable guidance throughout the research. He was very supportive and enthusiastic about this work making sure that we had a success story. I would like to extend my greatest appreciation to my committee members, Dr. D. Flaten and Dr. R. Gulden who helped me with constructive ideas and insightful comments in my thesis. Surely their inputs in this work, went a long way. I would also like to thank Dr. F. Zvomuya for letting us take their space for my growth chamber experiments. My sincere gratitude to the Manitoba Pulse and Soybean Growers, Alberta Pulse Growers, Saskatchewan Pulse Growers for providing financial support towards this research work. Special thanks to Lanny Gardiner, who at the onset of this research, helped me much with soil sampling. I could have not imagined pulling all the work without the hands of these wonderful technicians, Terri Fairman and Krista Hanis-Gervais, who helped me to their best regardless of the amount of work that needed to be done. Many thanks also to the following technicians; Brad Sparling, Mervin Bilous and Rob Ellis for their technical assistance. I am grateful to my colleagues Fernanda Gouvea-Pereira, Abhishek Agarwal, Mick Runzika and Nazanin Ghavami who made the lab a better place through their assistance and knowledge accompanied by tips on research and academic writing. My heartfelt gratitude goes to my mum and dad for their unfailing love, support and encouragement during my studies. They will forever be my cheerleaders. I would also like to thank my friend Tamuka for encouragement and raising prayers for me as I was conducting this work. Thank you everyone for your support and patience with me. Above all, I thank the Almighty God for grace and guidance throughout the academic phase. iii FOREWORD This thesis is organized into three chapters. Chapter 1 contains the introduction, literature review and research objectives. The second chapter will discuss the host preference of Pratylenchus spp. on the selected pulse and non-pulse crops in three replicate trials of a single growth cycle under growth chamber conditions. The chapter also covers the effects of host crops on Pratylenchus abundance following three crop growth cycles. The third chapter discusses the effect of Pratylenchus spp. on crop performance, endomigratory nature of the nematodes and the species identification of recovered nematodes. The thesis is organized in a “Sandwich” style as specified by the Faculty of Graduate Studies, and Department of Soil Science, University of Manitoba. The data chapters follow a manuscript format of the Journal of Nematology which they are intended to be published. The thesis closes with a general discussion of conclusions of the findings in the research work conducted and recommendations of future studies. iv TABLE OF CONTENTS Contents Page ABSTRACT ........................................................................................................................... ii ACKNOWLEDGEMENTS ................................................................................................. iii FOREWORD ........................................................................................................................ iv TABLE OF CONTENTS ....................................................................................................... v LIST OF TABLES ............................................................................................................. viii LIST OF FIGURES .............................................................................................................. ix LIST OF ABBREVIATIONS ................................................................................................ x 1 GENERAL INTRODUCTION .......................................................................................... 1 1.1. Major crop production in Canadian Prairies ............................................................... 1 1.2. The genus Pratylenchus .............................................................................................. 2 1.2.1. Morphology.......................................................................................................... 3 1.2.2. Hosts of Pratylenchus species ............................................................................. 3 1.2.3. Importance of Pratylenchus species .................................................................... 4 1.2.4. Pratylenchus species in Canada ........................................................................... 4 1.2.5. Symptoms caused by Pratylenchus species ......................................................... 5 1.2.6. Life cycle and reproduction ................................................................................. 6 1.2.7. Pathogenicity of Pratylenchus species. ................................................................ 7 1.2.8. Economic thresholds of Pratylenchus species ..................................................... 8 1.2.9. Survival strategies ................................................................................................ 9 1.2.10. Dispersal ......................................................................................................... 13 1.3. Factors affecting nematode population densities ...................................................... 13 1.4. Assessing host suitability to Pratylenchus species ................................................... 14 1.5. Plant disease complexes involving Pratylenchus species ......................................... 15 1.6. Identification of Pratylenchus species ...................................................................... 17 1.6.1. Morphological identification ............................................................................. 18 1.6.2. Molecular identification ..................................................................................... 19 1.7. Management of Pratylenchus species ....................................................................... 21 1.7.1. Cultural control .................................................................................................. 21 1.7.2. Plant resistance to Pratylenchus spp. ................................................................. 23 1.7.3. Pesticide Control ................................................................................................ 25 1.7.4. Integration of management strategies ...............................................................