[Truncated abstract] Lettuce Big-Vein Disease (LBVD) is a common chytrid- and soil-borne virus disease that affects lettuce in Western Australia. It causes chlorophyll clearing of the veins of the lettuce leaf, leaf crinkling and decreased head size, which together result in decreased yield and quality of lettuce. The phylogenetic relationships of Lettuce big-vein associated virus (LBVaV) and Mirafiori lettuce big-vein virus (MLBVV) and their vector Olpidium virulentus, associated with LBVD in Western Australia were established. Sources of inoculum in commercial lettuce seedling nurseries and commercial lettuce growing fields in south-western Australia were identified with an aim of improving strategies to manage the disease. Lettuce plants showing symptoms of lettuce big-vein disease were collected from the Perth Metropolitan region of south-west Australia and DNA extraction was done on their roots. When PCR primers designed specifically in this study were used to amplify the rDNA ITS region of O. brassicae and O. virulentus in extracts, only O. virulentus was detected. Phylogenetic analysis of the complete rDNA-ITS region sequences of the five Australian isolates and 10 others was done. The Australian isolates fitted within two clades of O. virulentus (I and II), and within clade I, into two of its four sub-clades (Ia and Id). LBVaV and MLBVV were both detected when symptomatic lettuce leaf tissue samples corresponding to the root samples of these plants were tested using virusspecific primers in Reverse Transcription-PCR. The presence of both viruses was found to be associated with O. virulentus occurrence. MLBVV, genus Ophiovirus, was detected in samples of big-vein diseased lettuce plants collected from seven different farms in south-west Australia. The complete coat protein (CP) gene encoding sequences of 13 isolates were obtained from these samples.
|Qualification||Doctor of Philosophy|
|Publication status||Unpublished - 2009|