Identification of two potyviruses of phaseolus vulgaris in South Africa

Master Thesis


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University of Cape Town

A survey was conducted by researchers at ARC-PPRI on dry beans (Phaseolus vulgaris) during 1993. All the viruses known to occur on dry beans in South Africa were found, as well as a few unidentified viruses. Of these, samples 93/1 and 93/65 form the basis of this thesis. Electron microscopy (EM) indicated that these viruses could be potyviruses, as they were flexuous particles of approximately 700 to 800 nm. Observation of pinwheels in ultrathin sections of Nicotiana benthamiana infected with isolate 93/1 and Phaseolus vulgaris infected with isolate 93/65, confirmed that the viruses probably belonged to the Potyvirus genus, family Potyviridae. Further serological tests indicated that the viruses were related but not homologous to strains of clover yellow vein (CIYW) and blackeye cowpea mosaic (BICMV) viruses respectively. None of these viruses have previously been described as occurring in South Africa. As we were unable to positively identify the viruses with serological methods, we needed to characterise these viruses on a molecular level. Potyvirus specific oligonucleotide primers were used for PCR amplification of viral eDNA The primers amplify an approximately 700 bp fragment of the virus genome, spanning the 3' noncoding region as well as a part of the coat protein gene: one primer is complementary to the poly(A) tail, and the other to a sequence coding for a conserved block of amino acid sequences (also known as the WCIEN block) in the mid-region of the coat protein. The nucleic acid sequences of the PCR products were compared to that of other potyviruses to positively identify these isolates.

Summary in English.

Bibliography: pages 105-125.