Bibliography: p. 410-429. / 429 p., [20] leaves of plates : ill. (some col.), map ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1995?

Bibliography: leaves 158-189.

Bibliography: p. 410-429.

Bibliography: leaves 170-189. This thesis looks at aphid feeding determinants by type and location. It examines the role of leaf surface chemicals in the discrimination of host plants and the deterrent effect of catechin and its oxidative condensation products.

Copies of author's previously published articles inserted. Bibliography: leaves 128-143. This thesis describes the development of serological and nucleic acid based diagnostic methods for pea-seed borne mosaic virus (PSbMV), the isolation of specific effects on infected pea plants, the collection and biological comparison of new PSbMV isolates from Pakistan, the cloning and sequencing of specific parts of the genome of selected isolates, nucleotide and amino acid sequence comparisons between selected isolates, and the development of a ribonuclease protection assay (RPA) for identifying genomic differences among the PSbMV isolates. It is the first comparison of a range of geographically different isolates of PSbMV on the basis of both biological and molecular properties.

Pallidosis is a disease of strawberry identified in 1957 with an unknown etiology. Two previously uncharacterized viruses in strawberry, Strawberry pallidosis associated virus (SPaV) and Beet pseudo-yellows virus (BPYV), have been found associated with disease symptoms. The complete nucleotide sequence of both viruses was determined and molecular detection protocols developed. In addition, an immunological tissue blot assay was developed for SPaV. Phylogenetic analysis of SPaV placed it in the genus Crinivirus, family Closteroviridae, along with BPYV. Transmission studies identified Trialeuroides vaporariorum, the greenhouse whitefly, as a vector of SPaV, while the virus was not transmitted by pollen or seed. The geographic distribution of both SPaY and BPYV in the United States was examined. Two ilarviruses of strawberry were investigated. Tobacco streak virus (TSV) is the type member of the genus Ilarvirus, family Bromoviridae, and can cause severe yield losses in small fruit crops. Sequence and phylogenetic analysis of 15 "TSV" isolates from Fragaria and Rubus revealed that they are homogeneous and represent a new virus species designated as Strawberry necrotic shock virus (SNSV). Nucleic acid-based protocols failed to identify any plants of the study infected with TSV an indication that the virus may not be a pathogen of Fragaria and Rubus. Fragaria chiloensis latent virus (FC1LV) is the second member of the genus Ilarvirus that infects strawberry. Previously, the virus had been found only in Chile and although many plants have been tested in North America using a serological test, none was found infected with the virus. A molecular test has been developed and used to confirm the presence of the virus in strawberries along the west coast of North America. Phylogenetic analysis of the coat protein gene of the virus place it in subgroup 4 of the genus along Prune dwarf virus, while it was previously thought to be related most closely to Lilac ring mottle virus and Asparagus virus-2. The role of the newly identified viruses and other viruses infecting strawberry is discussed in association with the strawberry decline disease found to cause severe symptoms and yield losses in both California and British Columbia, Canada. The significance of the work presented in this publication includes: the identification of two viruses associated with strawberry pallidosis disease; the complete nucleotide sequence of two criniviruses, an emerging group of plant viruses adds to the limited knowledge we have about this diverse virus genus; the identification of FC1LV in North America; the identification of SNSV as a distinct virus species which demonstrates the need of further studies on TSV, a virus species that infect a wide range of plant species and may actually be a cluster of diverse species. The high incidence of the pallidosis associated viruses points to the significance of the disease and their role in strawberry decline. The development of fast, sensitive and reliable tests for four strawberry viruses will have an impact to the strawberry industry, since the need for high quality, virus-free plants is essential for a crop that is asexually propagated. / Graduation date: 2004

Raspberry bushy dwarf virus (RBDV) is the sole member of the idaeovirus genus of plant viruses. It is a pollen-borne virus that economically impacts both red and black raspberries worldwide. Three strains of the bipartite RBDV have been reported. The common strain found in North America, South America, Australia, New Zealand and Europe and the resistance breaking strain found only in Europe are serologically indistinguishable while the black raspberry strain from North America is distinct. Resistance to RBDV is conferred by a single dominant gene, Bu. The resistance breaking strain is able to infect all raspberry cultivars containing the Bu loci. The sequence of a full-length clone of the common strain was determined and compared to the previously published sequence of the resistance breaking strain. Nucleotide homology between the two isolates was 97.6% for RNA 1 and 97.6% for RNA 2. Comparison of the predicted RNA 1 protein product of the two strains showed 97.9% homology. The predicted amino acid sequence of the movement protein and the coat protein from RNA 2 demonstrated 98.6% and 98.5% identity respectively. The differential rate of virus spread under field conditions in the Pacific Northwest was also investigated. The possibility of higher temperatures inhibiting virus infected pollen was explored by using in vitro germination and enzymatic staining procedures. Results from a two year study of virus-infected and virus-free raspberry pollen viability from both the Oregon and southern Washington region and the northern Washington and southern British Columbia region suggest temperature does not affect pollen germination or viability. Further studies were conducted to determine if a virus-degrading agent could be present on bee-stored raspberry pollen that becomes active only at higher temperatures. RBDV infected pollen from hives in northern Washington was collected and tested by ELISA after receiving either no heating or 32 hours of heating at 20, 30 or 40 C. Preliminary results indicate no such agent exists in red raspberry pollen from hives in the Pacific Northwest. / Graduation date: 2000

Fusarium spp. are among the most important pathogens of Douglas-fir (Pseudotsuga menziesii) seedlings in bareroot nurseries. Currently the most effective disease control method is soil fumigation with methyl bromide. As methyl bromide is phased out, however, other disease management strategies may become more important. We explored two alternative approaches to management of Fusarium diseases in Douglas-fir seedlings. The first approach was to transfer certain components of conifer forest soil, where Fusarium usually does not occur, to nursery soil, where Fusarium is often abundant. Specifically, we tested two hypotheses: (1) conifer forest soil contains a greater proportion of bacteria antagonistic in vitro to Fusarium than does nursery soil, and (2) pine needles, humic acid, ectomycorrhizal fungi, or bacteria obtained from forest soil will protect Douglas-fir seedlings against disease caused by soilborne Fusarium spp. if added to nursery soil. We did not find conclusive evidence to support either hypothesis. The second approach was to investigate the potential for biological control of seedborne Fusarium. Previous workers have shown, and we have confirmed in our studies, that Fusarium present on a small percentage of Douglas-fir seeds before cold stratification may spread during stratification; we recovered Fusarium from nearly all stratified seeds, representing three seedlots, plated on three culture media. When these seeds were planted in pasteurized soil, however, seedborne Fusarium did not cause significant disease in seedlings. Biological control of seedborne Fusarium during stratification may be important both to reduce the contribution of seedborne Fusarium to nursery soil and to protect germinants from soilborne Fusarium. We hypothesized that Pseudomonas chlororaphis isolate RD31-3A, a fluorescent pseudomonad previously shown to control Fusarium on Douglas-fir, would reduce the spread of Fusarium during stratification and protect seedlings from damping-off when seeds were planted into soil infested with pathogenic F. oxysporum. High populations of RD31-3A were recovered from seeds after stratification, and bacterial treatment reduced the spread of Fusarium without affecting seed germination or subsequent seedling dry weights. RD31-3A did not, however, protect seedlings from soilborne F. oxysporum. Nevertheless, seed treatment with bacteria during stratification may be an efficient way to deliver biological control agents to conifer seeds. / Graduation date: 1997

Experiments were done to determine pathogenic variability and pathogenic adaptation of Septoria tritici to different wheat cultivars. Fifteen S. tritici isolates from California, Oregon, and Texas were evaluated on seedlings of two sets of geographically diverse wheat cultivars under greenhouse conditions. Significant isolate effects, cultivar effects, and isolate X cultivar interactions were found, though the interaction terms were very small compared to the main effects of isolate and cultivar. All except one isolate were virulent to two sets of cultivars, and the virulence patterns varied among the isolate-cultivar combinations. Variability in virulence among the S. tritici isolates within and between locations also was observed. The isolates were usually more virulent to the cultivars of the same geographic origin than cultivars of other locations, and this demonstrates location-specific adaptation of S. tritici. Four populations of S. tritici, secured from four winter wheat cultivars grown in a field experiment, were evaluated on seedlings of the same wheat cultivars under greenhouse conditions. Significant spore population differences, cultivar differences, and spore population X cultivar interactions were obtained. The interaction term was fairly large compared to the main effect of spore population, and it is likely that the significant interaction was due to increased virulence of S. tritici to its own cultivar of origin. The "own" spore population (inoculation with spore population obtained from the same cultivar) produced significantly larger area under disease progress curve on the cultivar of origin than the "others" (inoculation with spore populations obtained from other cultivars), suggesting cultivar-specific adaptation of S. tritici. Spore populations obtained from the two susceptible cultivars indicated general adaptation to all of the test cultivars, whereas, the spore population secured from the most resistant cultivar showed specific adaptation to its cultivar of origin. Consequences of pathogenic variability, increased virulence, and adaptation of S. tritici to wheat cultivars are discussed. / Graduation date: 1994

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