Thesis (Ph. D.)--University of Adelaide, Dept. of Plant Pathology, 1985. / Includes bibliographical references (leaves 119-127).

Complementary DNA (cDNA) clones representing approximately 5800 nucleotides of potato leafroll virus (PLRV) genomic RNA were generated, restriction-mapped, and partially sequenced. Within one of the cDNA clones an open reading frame (ORF) that could encode a 23 kDa protein was identified and further characterized. Comparison of the deduced amino acid sequence with the coat protein amino acid sequence of the PAV strain of barley yellow dwarf luteovirus (BYDV-PAV) showed significant similarity. This observation together with its size and internal location within the genome suggested that this gene encoded the PLRV coat protein. Other similarities were observed between PLRV and BYDV sequences in this region of their genomes, including a 17 kDa ORF within the ORF encoding the 23 kDa coat protein, and termination of the latter with an amber codon which is immediately followed by a large ORF in the same reading frame. Three PLRV coat protein gene sequences were used to transform tobacco and the potato cultivars 'Desiree' and 'Russet Burbank' via Agrobacterium tumefaciens mediated gene transfers. One construct possessed 12 nucleotides of the untranslated leader sequence 5' to the putative coat protein gene start codon. The other construct, which was also inserted in the reverse orientation to produce negative-sense RNA, had 192 nucleotides from this leader sequence. When these sequences were introduced as chimaeric genes under the control of a duplicated cauliflower mosaic virus 35S (CaMV) promoter, transcription levels were high. Both positive-sense transcripts produced potato leafroll coat protein which accumulated to maximum levels of approximately 0.5% and 0.01% of total leaf protein in tobacco and potato, respectively. Results show that significant levels of inoculum concentration-independent sustained resistance were obtained with each construct, resulting in PLRV titres as low as 1% of the level observed in untransformed plants, as determined by enzyme-linked immunosorbent assays. Virus transmission from PLRV-inoculated transgenic 'Russet Burbank' was reduced substantially and was correlated with virus titre. The pattern and level of protection were the same for constructs producing positive- and negative-sense RNA, suggesting a similar mechanism of resistance. Virus levels were negatively correlated to transcript levels within the transgenic plants. This resistance will have practical applications for the control, of PLRV. Elucidation of the mechanism of resistance may also help understand the mechanisms of virus infection. / Land and Food Systems, Faculty of / Graduate

In total, 801 samples of potato leafroll disease were collected and tested for potato leafroll virus (PLRV) and beet western yellows virus (BWYV) in 1986, 1987, and 1988 using triple antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA) and virus-specific monoclonal antibodies. The samples represented 32 cultivars and originated in eight Canadian provinces and 12 American states. None of the samples tested positive for BWYV, whereas 772 (96.4%) tested positive for PLRV. Neither PLRV nor BWYV could be recovered, with aphid transfers to indicator hosts, from 28 of the 29 samples that tested negative for both viruses. PLRV was recovered from one sample that originally tested negative by TAS-ELISA; the indicator plant tested positive for PLRV by TAS-ELISA. Nucleic acid spot hybridization (NASH) using random primed and cloned cDNA probes was compared with double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) and TAS-ELISA, and aphid transmission tests for detection and identification of PLRV and BWYV in 165 potato leafroll disease samples. All of the samples tested negative for BWYV with each of the assay procedures. PLRV was detected in all of the samples with TAS-ELISA, NASH with a cloned cDNA probe for PLRV, and with aphid transmission to ground cherry (Physalis pubescens). Both DAS-ELISA and NASH using random primed cDNA produced one false-negative result. Shepherd's purse (Capsella bursa-pastoris) was a host for 72% (119/165) of the PLRV isolates. The susceptibility of potato to BWYV was tested by inoculating Russet Burbank with three isolates of BWYV from Canada and four from the United States. Two of the isolates were in a mixed infection with PLRV. None of the isolates were transmitted by Myzus persicae to virus-free potato plants, either by themselves or in association with PLRV. Common weeds were surveyed in the potato-producing areas of British Columbia for PLRV and BWYV. In total, 10,098 weed samples, representing 98 species in 22 plant families, were collected and tested by TAS-ELISA from 1986 to 1989. BWYV was detected in 1% of the samples; the hosts were: chickweed, common groundsel, heart-podded hoary cress, hedge mustard, little western bittercress, prickly lettuce, shepherd's purse, and wild radish. PLRV was detected in three volunteer potato plants, two samples of shepherd's purse, and one black nightshade plant. The low incidence of PLRV in plants other than potato indicates that weeds are of minor importance in the epidemiology of potato leafroll disease in British Columbia. / Land and Food Systems, Faculty of / Graduate

Thesis (Ph. D.)--University of Idaho, 2006. / Abstract. "May 2006." Includes bibliographical references. Also available online in PDF format.