The use of agroinfectious clones to investigate recombination between distinct maize streak virus strains
Doctoral Thesis
1998
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University of Cape Town
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The infectivity of the replicative form (RF) DNAs of MSV-Kom, MSV-Set and PanSV-Kar contained in the plasm ids pKom500, pSet100 and pPS100 was established by agroinoculating susceptible Jubilee sweetcorn with partial homodimeric Agrobacterium tumefaciens (C58C1) clones of RF-DNAs. Biological characteristics typical of Mastreviruses; such as, the appearance and leafhopper transmissibility of streak symptoms on infected plants, the presence of 18x30nm geminate particles in electron micrographs of leaf-dip preparations, and the presence of single-stranded and double-stranded DNA in Southern blot tests of infected plant DNA extracts, indicated that the RF-DNAs in pKom500, pSet100and PanSV-Kar represent the entire genomes of MSV-Kom, MSV-Set and PanSV-Karrespectively. The complete nucleotide (nt) sequence of the genome of MSV-Set was determined and characterised, and compared with those of MSV-Kom and PanSV-Kar. The genome sizes of MSV-Kom, MSV-Set and PanSV-Kar are 2701, 2690 and 2705 nt respectively, and all share Mastreviral genomic features. Phylogenetic analyses on the nt sequences and the putative amino acid sequences of the movement, coat and replication-associated proteins (MP, CP and Rep respectively) indicate that MSV-Set is grouped with, yet distinct from the MSV group of viruses isolated from maize. MSV-Set shares a 78% nt sequence identity with MSV-Kom which shares a >96% nt sequence identity with other MSVs. The PanSV-Kar genome shares a 60% nt sequence identity with the MSV group and89% with the Kenyan PanSV-Ken. PanSV-Kar causes mild non-persistent streak in Jubilee sweetcorn. MSV-Kom (previously isolated from maize in Komatipoort, Mpumalanga) and MSV-Set (previously isolated from a Setaria species in Mt. Edgecombe, Kwazulu/Natal) have different pathogenicities, and have overlapping, but non-identical, host ranges. Leafhopper transmission tests determined that MSV-Kom and MSV-Set generally cause severe and moderate streak in maize cultivars, or mild and severe streak in wheat cultivars respectively.
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Bibliography: pages 199-213.
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Schnippenkoetter, W. 1998. The use of agroinfectious clones to investigate recombination between distinct maize streak virus strains. University of Cape Town.