Angular Leaf Spot
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Management of common bean (Phaseolus vulgaris) angular leaf spot (Pseudocercospora griseola) using cultural practices and development of disease-weather models for prediction of the disease and host characteristics by David Icishahayo A thesis submitted in partial fulfillment of the requirements of the degree of Doctor of Philosophy Department of Crop Science Faculty of Agriculture University of Zimbabwe September 2014 ABSTRACT Bean seed collected from 82 households growing beans in Chinyika Resettlement Area indicated that sugar (sweet) bean type was the most preferred and cultivated by 84.1 % of farmers. The most common seed source was home-saved seed as indicated by 73.2 % of the farmers. Common seedborne fungi isolated from the different seed lots using the blotter method included; Fusarium oxysporum (73.2 %), Alternaria alternata (70.7 %) and Colletotrichum lindemuthianum (51.2 %). The major sources of inoculum identified for Pseudocercospora griseola were; infected seed, concomitant infected plants in the field, the soil at the end of the growing period, the air, rainfall and irrigation water. The north and south facing slides on the local trap were the most efficient in conidia trapping and the north conformed to the main wind direction which was north-north-east. A field study conducted on the control of common bean angular leaf spot (Pseudocercospora griseola) during two years (2002/3 and 2003/4) indicated that, as a consequence of unfavourable weather conditions for disease development, winter and early planting in summer associated with any irrigation method can be adopted. To target high yield, early planting can be complemented with any irrigation method, whereas the winter crop worked best with sprinkler irrigation. However, the high amounts of water received and high humidity conditions that prevail during maturity when beans are planted early might interfere negatively with harvesting operations and seed quality. This situation will require harvesting at physiological maturity, and putting in place facilities for drying plants/pods and seed after processing. The variables estimated at the start of the disease and leaf disease variables from 4 to 8 weeks after planting (WAP) [incidence, severity and defoliation], pod disease variables [incidence and severity], and weather variables from 4 to 10 WAP [duration of humidity and temperature, and daily mean humidity) were positively correlated with the main disease variables and negatively correlated with yield. Days to first disease infection and daily mean temperature were correlated negatively with the main disease variables and positively with yield. Duration of water and daily mean water were the most variable across evaluation periods, and correlations were specific to evaluation periods. For each one of the dependent variables, one most appropriate equation was developed and the number of predictors was reduced to 7 - 10. The most important predictors included in the equations developed; disease incidence and severity, mean daily humidity and water, duration of humidity and water, were associated with specific evaluation periods. Consequently, decisions can be made early enough to permit disease control measures and warn farmers. As soon as the conditions of water received and humidity favourable to the disease are recorded, farmers should be warned and control measures should be applied when necessary. The critical periods for disease infection were 4, 6 and 10 WAP. i ACKNOWLEDGMENTS I am grateful to my supervisor, Dr S. Dimbi for her advice and guidance. Her patience and understanding were a source of strength during difficult moments. I would like to thank Dr J. Sibiya, my former supervisor from the start of the research work, who offered a tremendous support, and constantly shared her knowledge. I also gratefully acknowledge invaluable guidance and advice from Mr B. Chipindu in agrometeorological data management, analysis and modeling. Dr S. Kageler, enthusiastically and freely gave me specialist biometrics advice especially in modeling. I would like to thank Prof. B.V. Maasdorp for having finalized the final proposal. Doctor E. Ngadze and Mrs E. Masenda should be commended for their guidance in research methodology and assistance in the laboratory work. Many useful comments were received from Drs W. Manyangarirwa, I. Makanda, A. B. Mashingaidze, R. and C. Madakadze. I am grateful to Dr A. Murwira for his help in the estimation of the distances between stations, Dr S. Dzikiti in weather data calculations, Dr E. Mashonjowa for his advice in the management of wind direction data, and Dr A. Senzanje for his contribution in sprinkler and furrow irrigation weather data adjustment. I am grateful to Dr C. Mguni who allowed me to use Mazowe Quarantine laboratory facilities and to the personnel of the institution especially Mrs M. Mabika, D. Mukwena and A. Semani. I thank also A. Matikiti, G. Ashley, M. Cavill and A. Mare for their assistance in laboratory work. I am also grateful to Agricultural and Rural Development Authority Muzarabani (ARDA Mz) staff, to P. Kambidzi, L.Tumbare and R. Tumbare for their contribution in field experimentation. Givemore Parirenyatwa was the key person in the Chinyika seed collection. I would like to thank Agricultural Technical and Extension Services (AGRITEX) personnel, S. Marimo, N. Gachange and all the people who assisted in seed collection. I would like to thank Dr S. Dimbi and Mrs T. Sigobodhla for having provided the Burkard trap used in this research. I thank A. Chirwa, M. Mlambo and R. Cikotosa of the Engineering Department for their contribution in making the local trap, installing and maintaining the traps used in the study. I am grateful to Belvedere weather station staff especially Mr T. Gwaze, and to Mr T. Soko of Seed-Co Rattray Arnold Research Station for sourcing meteorological data used in this study. Financial assistance from The Rockefeller Foundation, the Southern Africa Bean Research Network and the Crop Breeding Institute is gratefully acknowledged. I thank Fr F. Chanterie, Mr M. Triest, Miss T. Masekesa and Mrs S. Svova for their contribution in this study. There are many others who directly and indirectly contributed to the success of this study, and to you all, I say: thank you. Lastly I thank the Virgin Mary and Christ. ii TABLE OF CONTENTS ABSTRACT ..................................................................................................................................... i ACKNOWLEDGMENTS .............................................................................................................. ii TABLE OF CONTENTS ............................................................................................................... iii LIST OF TABLES ....................................................................................................................... viii LIST OF FIGURES .........................................................................................................................x LIST OF APPENDICES .............................................................................................................. xiii LIST OF ABBREVIATIONS ...................................................................................................... xiv CHAPTER 1: INTRODUCTION AND JUSTIFICATION ............................................................1 1.1 General introduction ................................................................................................1 1.2 Objectives of the study.............................................................................................6 1.3 Study hypotheses .....................................................................................................7 CHAPTER 2: GENERAL LITERATURE REVIEW ....................................................................9 2.1 Introduction….. ........................................................................................................9 2.2 Angular leaf spot ......................................................................................................9 2.2.1 Sources of inoculum, survival and symptom development .......................10 2.2.2 Control of angular leaf spot disease in beans.............................................11 2.3 Effect of weather factors on plant disease development ........................................15 2.3.1 Temperature ...............................................................................................15 2.3.2 Moisture .....................................................................................................16 2.3.3 Combination of weather variables .............................................................17 2.4 Conditions suitable for disease-free bean production ............................................17 2.5 Irrigation……. .......................................................................................................19 2.5.1 Sprinkler irrigation .....................................................................................20 2.5.2 Effect of irrigation systems on diseases infection and yield ......................20 2.6 Date of planting......................................................................................................22 2.7 Overview of modeling possibilities .......................................................................23 2.7.1 Simulation models .....................................................................................24 2.7.2 Statistical models .......................................................................................24