Abraham Adane (Professor)Tesfaye Kassahun (Professor)Guadie Demsachew2020-10-212023-11-182020-10-212023-11-182019-10-10http://etd.aau.edu.et/handle/12345678/22884Maize (Zea mays L.) is leading cereal crop in terms of production in Ethiopia. However, achieving its yield potential is hindered by a number of biotic and abiotic factors. To enhance its productivity, these limiting factors should be addressed. Among the biotic factors, more than 50 viruses can infect and cause disease on maize. Of these, the rapidly emerged maize lethal necrotic disease (MLND) and maize streak disease (MSD) were reported to have high yield loss potential. This study was initiated to survey maize fields, study associated virus diseases and examine their diversity in Ethiopia. A total of 284 maize fields from five major maize growing regions were surveyed in four survey missions between 2015 and 2017, of which 846 leaf samples with virus like disease symptoms were collected from 191 fields. Ninety three fields with no observable symptoms were exempted from sampling. Up to 100% disease incidence was recorded in the Benishangul-Gumuz, Oromia and South Nations, Nationalities and People (SNNP) regions. In the first set of test experiment double or triple antibody sandwich enzyme-linked immuno-sorbent assay to test for eight common maize viruses confirmed the presence of Maize chlorotic mottle virus (MCMV), Sugar cane mosaic virus (SCMV) and Maize streak virus (MSV). MLND was the most important disease in SNNP and Oromia while MSD was predominant in Benishangul-Gumuz. Sequence analysis of coat protein genes of these three viruses showed little variability. In the test experiment for mastreviruses, three genetic groups, each representing distinct virus species were identified. The first group represented the A-strain of MSV. The second sequence group shared 96-98% identity with Maize streak reunion virus (MSRV) isolates, confirming the presence of MSRV also in continental East Africa for the first time. Sequence analysis of additional virus genomes (each 2846 nt) representing the third group revealed only a limited nucleotide identity of 70-71% with MSRV isolates belonging to a novel virus species tentatively named maize streak dwarfing virus (MSDV). PCR screening of 89 iv samples showing streak symptoms with designed general or specific mastrevirus primers showed that MSV is the most incident followed by MSRV and MSDV. Maize yellow mosaic virus (MaYMV) was also assessed from 47 leaf samples by RT-PCR using general polerovirus primer pairs embracing 325 nucleotides of the coat protein gene 34 samples were positive for this primer. Direct sequencing of the RT-PCR products confirmed ≥ 99% nt identity to each other and shared 98 to 99% identity with the reference sequence, KU248489. Full-genome sequence variability study of three MaYMV isolates using Illumina MiSeq sequencing revealed 99.6% nt identity to each other. One of the complete genome sequences, MF684369 shared 96.8% nt identity with KU248489. In conclusion, this study revealed the presence of six viruses in maize fields of Ethiopia, their distribution, incidence and provided sequence data for these viruses. Moreover, occurence of three different mastrevirus species on maize in Ethiopia, is unprecedented, and suggests that Ethiopia may be one of the potential hot spots for the diversity of maize mastreviruses.enElisaIllumina MiseqIncidenceMaize VirusesRcaThesis