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The Effect of Silicon on Strawberry Plants and It's Role in Reducing Infection by Podosphaera Aphanis

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The Effect of Silicon on Strawberry Plants and It's Role in Reducing Infection by Podosphaera Aphanis The effect of silicon on strawberry plants and it’s role in reducing infection by Podosphaera aphanis Kaneez Fatema Thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy University of Hertfordshire School of Life and Medical Sciences Department of Human and Environmental Sciences Hatfield, AL 10 9AB UK July 2014 Acknowledgements I would like to thank all the people who have encouraged and supported me during this period. In particular, I am very grateful to my supervisors, Dr. Avice Hall, and Dr. David Naseby for their constant support, guidance and advice during the course of my PhD. Their expertise in different areas has allowed me to develop a wide range of techniques in the laboratory. I would also like to acknowledge all the academic, technical staff and fellow PhD student of the School of Life and Medical Sciences for creating the right atmosphere that enabled the completion of these studies. I would like to thank Gidon Bahiri (King’s Lynn, Norfolk) to supply Omex SW7 for this experiment and Andy and Helen Barker for carrying out the spraying and special thanks goes to Harriet and Henry Duncafe (Maltmas Farm) who gave extremely generously of their time and contributed significantly to the success of this work and also providing runners and field trial facilities, I appreciate the financial support from Hall Charitable Trust and Charles Wallace Bangladesh Trust, UK. Finally, I would like to thank my husband Dr. Waliul Hoque Chowdhury for his support, patience and encouragement and also my daughter Nahian Chowdhury and son Faiyaj Chowdhury and my parents for their constant support and encouragement throughout the duration of my PhD. ii Abstract Podosphaera aphanis which causes powdery mildew of strawberry is of economic importance in strawberry production in United Kingdom as it affects yield and fruit quality. Silicon has been shown to reduce the severity of a number of plant diseases. In strawberry, the mechanism of suppression against powdery mildew remains uncertain. Therefore, it has been suggested that supplying silicon would help strawberry plants to absorb silicon and improve resistance against the pathogen. The silicon based wetter Omex SW7 was used and three different concentrations of silicon wetter were applied on the leaves of the strawberry plants (foliar application). Each treatment was applied at three different timings. Enhanced level of silicon was quantified by the Autoclave Induced Digestion (AID) method. Whilst the main study has used the variety Elsanta, other varieties have also been used. It was observed that the weekly application (total 5 sprays) of 3 different concentrations of Omex SW7 on leaves showed significantly (P<0.05) higher silicon concentrations compared to application 3 times in weeks 1, 3 and 5 or twice in weeks 1 and 5. Microscopic observations showed that weekly application of standard, high and very high concentrations of Omex SW7 significantly (P<0.05) increased the number and length of leaf hairs on both the upper and lower surfaces of strawberry leaves. The different varieties of strawberry used showed morphological changes in the leaves with regard to the density and length of leaf hairs. Untreated leaves from Rhapsody had no hairs on the upper leaf surface, but a low density of hairs was observed after treatment with the high concentration of Omex SW7. In this study, Omex SW7, a silicon based wetter was applied to the roots of strawberry plants (root application) and silicon accumulation and physical changes in leaves were assessed. Strawberry variety Elsanta was used in this experiment. Results revealed that weekly application (total 5 applications) of 2 different concentrations (standard and high) of Omex SW7 to roots showed significantly (P<0.05) higher silicon concentrations compared to application 3 times in weeks 1, 3 and 5 or twice in weeks 1 and 5. It was found that the weekly application of two different concentrations of Omex SW7 showed significantly higher (P<0.05) leaf hair numbers and significantly (P<0.05) longer leaf hair length on both the upper and lower surfaces of leaves compared to application 3 times in weeks 1, 3 and 5 or twice in weeks 1 and 5. The effect of foliar application of silicon and potassium carbonate to limit P. aphanis infection was examined in a field trial under polythene tunnel at Wisbech. Treatments were arranged in a randomised block design of 3 replicates. There were a total of 18 plots. There were six treatments and all treatments were applied to the strawberry variety Sonata. Results revealed that application of silicon based wetter Omex SW7 onto the leaf surface does result in accumulation of silicon in the leaves. The application of Omex SW7 has stimulated an increase in the number and length of leaf hairs in strawberry plants. Results showed that germinating ascospores and colonies were present in all plots before the trial was sprayed. Treatments with standard and high Omex SW7 significantly (P<0.05) reduced the number of germinating ascospores and colonies in this trial. However, Potassium carbonate alone gave some reduction in the number of colonies and germinating ascospores. Moreover, potassium carbonate mixed with silicon based wetter Omex SW7 significantly (P<0.05) reduced the number of germinating ascospores and colonies. iii List of Contents Title Page i Acknowledgements ii Abstract iii List of contents iv List of Figures xi List of Tables xviii Appendix xx Chapter 1 General Introduction 1 1.1. Introduction 1 1.2. Literature Review 3 1.2.1. Strawberry Plant 3 1.2.2. Polythene tunnel production of strawberries 6 1.2.3. Strawberry cultivation methods 8 1.2.3.1. Varieties 8 1.2.3.2. Planting 10 1.2.3.3. Spacing 12 1.2.3.4. Watering/Irrigation 12 1.2.3.5. Continuing care 13 1.2.3.6. Polythene tunnel management 13 1.2.3.7. Fertilizer 15 1.2.3.8. Pollination 15 1.2.3.9. Harvesting 16 1.2.3.10. Pests and diseases in strawberry crops 16 iv 1.2.4. Strawberry powdery mildew 18 1.2.4.1. Classification 18 1.2.4.2. Economic loss caused by powdery mildew 19 1.2.4.3. Symptoms of infection 20 1.2.4.4. Reproduction of powdery mildew 21 1.2.4.5. Environmental requirements of the fungus P. aphanis 26 1.2.4.5.1. Effect of temperature 26 1.2.4.5.2. Effect of humidity 27 1.2.5. Control of powdery mildew 28 1.2.5.1. Chemical control 28 1.2.5.2. Integrated control methods 29 1.2.5.3. Biocontrol agents to control powdery mildew 31 1.2.6. Role of silicon in plants 34 1.2.6.1. Silicon uptake in plants 35 1.2.6.2 Effects of silicon on plant growth and development 36 1.2.6.3. Silicon and disease resistance in plants 36 1.2.6.4. Effect of silicon on diseases caused by abiotic stresses 39 1.2.7. Leaf hairs 41 1.2.8. Silicon wetter Omex SW7 41 1.2.9. Potassium carbonate (K50) 42 1.3. Rationale, Aims and Objectives 42 1.3.1 Rationale 42 1.3.2. Hypothesis 43 1.3.3. Aims and Objectives 43 v 1.3.3.1. Aim (overall aim) 43 1.3.3.2. Objectives 43 Chapter 2 General Materials and Methods 44 2.1. Elsanta 44 2.2. Symphony 44 2.3. Florence 44 2.4. Rhapsody 44 2.5 Growing strawberry plants in the Glasshouse 45 2.6. Application of the treatments 46 2.7. Silicon determination 47 2.7.1. Determination of the standard curve 47 2.7.2. Methods for extraction of silicon from strawberry leaves 48 2.7.2.1. Preparation of solutions 48 2.7.2.2. Extraction of silicon from ground leaves 49 2.7.2.3. Determination of silicon in the different treatments 50 2.8. Microscopic observation of density and length of leaf hairs 51 2.9. Data analysis 51 Chapter 3 An investigation of the effect of foliar application of silicon 52 (Omex SW7) on strawberry plants in the glasshouse 3.1. Introduction 52 3.1.1. Objectives 53 3.2. Materials and Methods 53 3.2.1. Pilot experiment 53 3.2.1.1. Application of the treatments 56 vi 3.2.1.2. Collection of leaves 56 3.2.2. Main experiment 57 3.2.2.1. Application of the treatments 57 3.2.2.2. Collection of leaves 58 3.2.3. Main experiment (used different varieties) 61 3.2.3.1. Application of the treatments 61 3.2.3.2. Collection of leaves 64 3.2.4. Data analysis 65 3.3. Results 65 3.3.1. Pilot experiment in Hatfield Glasshouse 65 3.3.2. Main Experiment in Bayfordbury Glasshouse 68 3.3.3. Effect of timing on silicon concentrations in strawberry leaves 69 3.3.4. Effect of silicon on the density of leaf hairs 73 3.3.5 Relationship between the leaf hair numbers and accumulation of 76 silicon 3.3.6. Effect of silicon on the length of leaf hairs 77 3.3.7. Relationship between the length of leaf hairs and accumulation of 79 silicon 3.3.8. Effect of treatments on accumulation of silicon in different 80 strawberry varieties 3.3.9. Effect of silicon on the density of leaf hairs in different 82 strawberry varieties 3.3.10. Relationship between the leaf hair numbers and accumulation of 84 silicon (different varieties) 3.3.11. Effect of silicon on the length of leaf hairs in different strawberry 85 varieties 3.3.12.
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