Browsing by Author "Van der Walt, Eric"

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    Experimental investigations of mastrevirus molecular biology and evolution
    (2008) Van der Walt, Eric; Rybicki, Ed; Martin, D P
    This dissertation describes three major sets of experiments, all of which involved the construction and use of various reciprocal chimaeric MSV constructs. First, chimaeric viruses were used in genetic complementation-type experiments to investigate the biological significance of interactions between the two virion-sense open reading frames (ORFs) of MSV, their products, and the rest of the genome. Six chimaeric MSV constructs were made by reciprocally exchanging the ORFs encoding movement protein (MP) and coat protein (CP) individually, and in pairs, between MSV-Kom and MSV-Set, which share just 78% overall nucleotide identity. Analysis of symptomatology and infection efficiency of chimaeras and wild-type parental viruses revealed evidence of functionally relevant specific interactions between MSV MP and CP.
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    Maize streak virus: an old and complex 'emerging' pathogen
    (Wiley, 2010) Shepherd, Dionne N; Martin, Darren P; Van der Walt, Eric; Dent, Kyle; Varsani, Arvind; Rybicki, Edward P
    Maize streak virus (MSV; Genus Mastrevirus, Family Geminiviridae) occurs throughout Africa, where it causes what is probably the most serious viral crop disease on the continent. It is obligately transmitted by as many as six leafhopper species in the Genus Cicadulina, but mainly by C. mbila Naudé and C. storeyi. In addition to maize, it can infect over 80 other species in the Family Poaceae.Whereas 11 strains of MSV are currently known, only the MSV-A strain is known to cause economically significant streak disease in maize. Severe maize streak disease (MSD) manifests as pronounced, continuous parallel chlorotic streaks on leaves, with severe stunting of the affected plant and, usuallly, a failure to produce complete cobs or seed. Natural resistance to MSV in maize, and/or maize infections caused by non-maize-adapted MSV strains, can result in narrow, interrupted streaks and no obvious yield losses. MSV epidemiology is primarily governed by environmental influences on its vector species, resulting in erratic epidemics every 3–10 years. Even in epidemic years, disease incidences can vary from a few infected plants per field, with little associated yield loss, to 100% infection rates and complete yield loss.