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The Effect of Potyvirus Resistance on Maize Lethal Necrosis (Mln)

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THE EFFECT OF POTYVIRUS RESISTANCE ON MAIZE LETHAL NECROSIS (MLN) THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By VICTORIA BIKOGWA BULEGEYA Graduate Program in Horticulture and Crop Science The Ohio State University 2016 Master's Examination Committee: Professor DAVID M. FRANCIS “Advisor” Professor MARGARET G. REDINBAUGH “Co-advisor” Professor PETER R. THOMISON Copyrighted by VICTORIA BIKOGWA BULEGEYA 2016 Abstract Maize lethal necrosis (MLN) is a viral disease of corn (Zea mays L.) currently affecting farmers in East and Central Africa. MLN is caused by a combined infection of Maize chlorotic mottle virus (MCMV) and any potyvirus. In East Africa, MLN was reported to be caused by a combined infection of MCMV and Sugarcane Mosaic virus (SCMV). Most of African maize germplasm is susceptible to the disease and there are no known sources of resistance. Resistance to MCMV has not been well studied but tolerant germplasm has been reported in the US. Resistance to the potyvirus pathogens of maize is well studied and sources of resistance are known and published. This study utilize available potyvirus resistance sources to control MLN and to link potyvirus resistance to white maize endosperm color which is preferred by consumers in Sub Saharan Africa. Lines with different QTL for potyvirus resistance were screened against MLN using artificial inoculation and natural infestation. Genotypes used for the study were Recombinant inbred lines (RIL) derived from Oh1VI, a line known for multi-virus resistance, and Oh28 which is a susceptible parent. Genotypes, with QTL for potyvirus resistance on chromosome 3, 6 and 10 alone and in combination were selected and screened against MLN. Experiments were set in the growth chamber at OARDC Wooster, Ohio and MLN was inoculated using US isolates of MCMV and SCMV. Experiments were also planted in a field at the Naivasha MLN screening facility in ii Kenya, where field inoculation was done using African isolates of MCMV and SCMV. Experiments were also set in MLN hotspots in Arusha and Babati, Tanzania, under natural infection. Study results show significant differences among genotypes and QTL groups at P=0.05 in experiments in the growth chamber and at Babati under natural infection. In all experiments showing differences among genotype groups with different QTL, a combination of 3, 6 and 10 provided MLN control as reflected by low MLN scores. The study also selected for genetic linkage between potyvirus resistance and white endosperm color to bring resistance into the white maize background which is preferred by farmers and consumers in East Africa. The study used a yellow resistant line Pa405 and white susceptible lines CML333 and CML277 to generate F2 progenies which were screened using molecular markers (SSR) to select for recombinants with white endosperm and potyvirus resistance. Twenty one recombinants were selected, self- pollinated, and progeny were screened for resistance to SCMV and MDMV. Six progenies were resistant to MDMV and 4 recombinants were segregating for resistance to SCMV, suggesting that coupling phase recombination was established in these families. The recovered recombinants with white endosperm and potyvirus resistance can be used in breeding programs for introgression of resistance into the preferred food-grade genetic backgrounds. The results of this study provide useful baseline information for more research on MLN resistance and MLN control in Sub Saharan Africa. iii Dedicated to my family iv Acknowledgments I am very thankful to my advisors Dr. David Francis and Dr. Margaret Redinbaugh for their guidance and support in the journey of my coursework and research to complete my degree. My extended gratitude goes to my other committee member Dr. Peter Thomison for his continuous support and advice to ensure I excel in my graduate studies. My sincere thanks go to Mark Jones and to all members of the USDA, ARS Corn, Soybean and Wheat Quality Research Unit (CSWQRU) in Wooster for their technical and moral support. I am also very grateful to all members of Dr. Francis’ lab at Williams’s hall, OARDC, Wooster for their generous support to accomplish my work in the lab and green house. My thanks also go to my Tanzanian advisor, Dr. George Muhamba for his commitment and support to ensure my work was successful in Tanzania. My gratitude also goes to Kheri Kitenge and his team at ARI-SELIAN in Arusha Tanzania for their support in setting up my field trials. My genuine thanks also go to Dr. Biswanath Das and all member of CIMMYT Kenya for their support to conduct my experiments at Naivasha, Kenya and for mentoring me during my studies. I deeply appreciate the USAID feed the future program under iAGRI-Tanzania for funding my studies and the Borlaug LEAP fellowship for funding part of my research work in Kenya. My extended thanks go to my husband, son, parents and in-laws for their continuous support during the time of my studies. I will always remember your kindness. v Vita 2010 ........................................................... B.Sc. Environmental science and management, Sokoine University of Agriculture, Tanzania. 2012 ............................................................ Agriculture research officer, Ministry of agriculture livestock and fisheries at Ilonga agriculture research station, Tanzania. 2014 to present ........................................... Graduate student, Department of horticulture and crop science, The Ohio State University, USA. Fields of Study Major Field: Horticulture and Crop Science vi Table of Contents Abstract .......................................................................................................................... ii Acknowledgments ...........................................................................................................v Vita ............................................................................................................................... vi Table of Contents ......................................................................................................... vii List of Tables................................................................................................................ xii List of Figures ........................................................................................................... xviii CHAPTER 1 : INTRODUCTION AND LITERATURE REVIEW .................................1 1.1. Introduction ..............................................................................................................1 1.1.2. Research objective ..........................................................................................2 1.1.3. Research hypothesis ........................................................................................3 1.1.4. Research significance ......................................................................................3 1.2. Literature review .......................................................................................................6 1.2.1. Maize in Sub Saharan Africa and Tanzania. ....................................................6 1.2.2. Maize Lethal Necrosis distribution in Sub Saharan Africa. ..............................6 1.2.3. Causes of Maize lethal necrosis.......................................................................7 1.2.3.1. Maize chlorotic mottle virus .........................................................................8 1.2.3.2. Potyviruses ..................................................................................................8 1.2.3.3. Synergism. ...................................................................................................9 vii 1.2.4. Host range of Maize lethal necrosis ............................................................... 10 1.2.5.1 Plant disease resistance ............................................................................... 10 1.2.5.2. Screening for virus resistance in maize ....................................................... 12 1.2.5.3. Screening for resistance against MLN disease ............................................ 13 1.2.5.4. Role of potyvirus resistance in Maize lethal necrosis control. ..................... 13 1.2.6 Endosperm color in maize ............................................................................. 15 1.2.6.1. Y1 locus..................................................................................................... 16 1.2.6.2. Location of the Y1 gene ............................................................................. 17 1.2.6.3. Maize color preference in SSA ................................................................... 17 1.2.6.4. Potyvirus resistance and endosperm color in maize .................................... 18 References ..................................................................................................................... 20 CHAPTER 2 : Response of potyvirus resistant maize genotypes to inoculation with Maize lethal necrosis (MLN) ....................................................................................... 30 2. 1. Abstract ................................................................................................................. 30 2.2. Introduction ............................................................................................................ 31 2.3 Materials and methods ............................................................................................
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