SOYBEAN RESPONSE TO RUST AND SCLEROTINIA STEM ROT UNDER DIFFERENT BIOTIC AND ABIOTIC CONDITIONS CHRISNA STEYN Submitted in accordance with the requirements for the degree PHILOSOPHIAE DOCTOR In the Faculty of Natural and Agricultural Sciences Department of Plant Sciences (Plant Pathology) University of the Free State Bloemfontein South Africa Promoter: Prof. N.W. McLaren June 2015 TABLE OF CONTENTS DECLARATION ............................................................................................................... i DEDICATION .................................................................................................................. ii ACKNOWLEDGEMENTS .............................................................................................. iii GENERAL INTRODUCTION ......................................................................................... iv References .............................................................................................................. viii CHAPTER 1 .................................................................................................................... 1 AN OVERVIEW OF SCLEROTINIA STEM ROT AND SOYBEAN RUST IN SOUTH AFRICA .......................................................................................................................... 1 1.1 Introduction .......................................................................................................... 1 1.2 Soybean production statistics ............................................................................ 1 1.3 Sclerotinia stem rot ............................................................................................. 3 1.3.1 Symptoms and signs .................................................................................... 3 1.3.2 Host range and distribution .......................................................................... 5 1.3.3 Economic Importance ................................................................................... 7 1.3.4 Epidemiology ................................................................................................ 8 1.3.5 Genetic variability ....................................................................................... 10 1.3.5.1 Fingerprinting techniques .................................................................... 12 1.3.6 Chemical control ......................................................................................... 13 1.3.7 Breeding for resistance .............................................................................. 16 1.3.8 Mechanisms of resistance and pathogenicity ........................................... 18 1.4 Soybean rust ...................................................................................................... 20 1.4.1 Symptoms and signs .................................................................................. 20 1.4.2 Host range and distribution ........................................................................ 25 1.4.3 Economic importance ................................................................................. 27 1.4.4 Epidemiology ............................................................................................... 28 1.4.5 Genetic variability ....................................................................................... 30 1.4.6 Chemical control ......................................................................................... 31 1.4.7 Breeding for resistance .............................................................................. 32 1.4.8 Mechanisms of resistance and pathogenicity ........................................... 37 1.5 Conclusion ......................................................................................................... 38 1.6 References ......................................................................................................... 38 CHAPTER 2 .................................................................................................................. 61 EPIDEMIOLOGICAL FACTORS TO BE CONSIDERED DURING THE EVALUATION OF SOYBEAN LINES FOR RESISTANCE TO SOYBEAN RUST CAUSED BY PHAKOPSORA PACHYRHIZI IN SOUTH AFRICA ...................................................... 61 2.1 Abstract .............................................................................................................. 61 2.2 Introduction ........................................................................................................ 62 2.3 Materials and methods ...................................................................................... 63 2.3.1 Greenhouse evaluation ............................................................................... 63 2.3.1.1 Inoculum production ............................................................................ 63 2.3.1.2 Plant production ................................................................................... 64 2.3.1.3 Inoculation procedure .......................................................................... 64 2.3.1.4 Ratings and data analysis .................................................................... 64 2.3.2 Field evaluation ........................................................................................... 65 2.3.2.1 Field plots .............................................................................................. 65 2.3.2.2 Ratings and data analysis .................................................................... 65 2.4 Results ................................................................................................................ 66 2.4.1 Greenhouse evaluation ............................................................................... 66 2.4.2 Field evaluation ........................................................................................... 67 2.5 Discussion ......................................................................................................... 68 2.6 References ......................................................................................................... 71 CHAPTER 3 .................................................................................................................. 84 VARIATION IN YIELD ASSOCIATED WITH SOYBEAN RUST EPIDEMICS IN SOUTH AFRICA ........................................................................................................................ 84 3.1 Abstract .............................................................................................................. 84 3.2 Introduction ........................................................................................................ 85 3.3 Materials and Methods ...................................................................................... 87 3.3.1 Field trials .................................................................................................... 87 3.3.2 Crop and disease assessment ................................................................... 88 3.3.3 Data analysis ............................................................................................... 88 3.4 Results ................................................................................................................ 89 3.5 Discussion ......................................................................................................... 91 3.6 References ........................................................................................................ 95 CHAPTER 4 ................................................................................................................ 105 PHYSIOLOGICAL CHANGES DURING THE GROWTH OF SOYBEAN AND THEIR EFFECT ON SUSCEPTIBILITY TO SOYBEAN RUST CAUSED BY PHAKOPSORA PACHYRHIZI .............................................................................................................. 105 4.1 Abstract ............................................................................................................ 105 4.2 Introduction ...................................................................................................... 106 4.3 Materials and Methods .................................................................................... 107 4.3.1 Plant production ........................................................................................ 107 4.3.1.1 Evaluation of resistance mechanisms to soybean rust in commercial cultivars from different maturity groups ....................................................... 107 4.3.1.2 Nitrogen treatments ............................................................................ 108 4.3.2 Disease measurement and data analysis ................................................ 108 4.3.3 C ollection of Intercelluar wash fluids (IWF) ............................................ 109 4.3.4 Determination of protein concentration ................................................... 109 4.3.5 Determination of enzyme activities .......................................................... 110 4.3.5.1 β-1,3-glucanase activity ...................................................................... 110 4.3.5.2 Chitinase activity ................................................................................ 110 4.3.5.3 Peroxidase activity ............................................................................. 111 4.3.6 Determination of total phenolics .............................................................. 111 4.3.7 Determination of total carbohydrates