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These studies compared giant hill strains of Russet Norkotah and Umatilla Russet to the parent varieties. Selections were initially based on late maturity and increased vine vigor. Subsequent evaluations emphasized yield and quality parameters in comparison to the parent varieties. Giant hills were collected from the Columbia Basin and Central Oregon in 1999. Seed was tested and increased in a greenhouse during the winter of 1999 and in the field in 2000. Clones were inspected for viruses and other diseases in both years. Replicated performance trials were conducted at the Hermiston Agricultural Research and Extension Center in the Columbia Basin and at the Central Oregon Agricultural Research Center, near Madras, in 2001. Trials were grown using commercial management practices common to the areas. Tubers from the Madras trial were retained for use in future plantings. Relative yields of Russet Norkotah strains differed drastically between sites even though the growing seasons were similar in length. Several Russet Norkotah strains preformed better than the parent variety at Madras when the strains achieved good vine growth and the parent variety did not. Vine growth was subnormal at Madras in 2001 primarily due to delayed emergence and the subsequent short growing season. Few performance differences and no advantages were evident when Russet Norkotah strains were grown in the Columbia Basin under conditions with less environmental stress than usual. All strains of Umatilla Russet grown under a long season in the Columbia Basin out-yielded the parent variety; however, many strains also produced a high percentage of malformed tubers. In general, Umatilla Russet strains failed to produce adequate yields and tubers of acceptable size when delayed emergence shortened the growing season at Madras. At Madras, strains of Umatilla Russet with high biomass tended to have lower yields while strains of Russet Norkotah with high biomass tended to have high yields. Some strains performed better than the parent varieties at the two trial sites. Superior strains have been submitted to the Oregon Potato Variety Development Program and Oregon Foundation Potato Seed Project for further evaluation. / Graduation date: 2002

The culture in vitro was investigated in 7 clones of roses representing a range of genotypes and ploidy levels. Particular attention was paid to a sterile hybrid, R. persica x xanthina , from which it was hoped to obtain tetraploid clones. It was anticipated that tetraploid clones might be fertile and that this would facilitate introgressive hybridization of R.persica genes into various classes of cultivated roses. Propagation medium was developed based on MS salts and vitamins supplemented with BAP and NAA. Doubling times of 2-4 weeks were obtained on optimum media. Transplantation to soil was achieved with R.wichuraiana had a 99% success rate _____ conditions when a misting system was used whereas transplantation with R.ruRpsa 'Scabrosa' was only 46% successful and no success was achieved with R.persica x xanthina . Success rates were subsequently improved R.persica varying degrees of success, on transfer to in vivo to 80% with 'Scabrosa' and Sorbarod plugs prior to transplantation. Whilst in culture adventitious shoots were induced clones (R.laevigata , R.wichuraiana and R.persica R.persica shoots x xanthina by the use of from leaves of 3 x xanthina ) but only with adventitious callus. The cell established _____ procedure. This was exposure to colchicine gave x xanthina from _____ did it prove possible to induce internodal stem segments, roots, leaves and the cycle time of in vitro as 10.25 hours used in discussing diploid rose R.wichuraiana was using an autoradiographic the optimal duration of solution. It was complete spindle inhibition without a found that reduction 0.05% colchicine mitotic index. in The addition of DMSO was shown to aid the uptake of colchicine into shoot meristems. Terminal buds of R.wichuraiana and R.persica x xanthina were exposed level to colchicine solution in plants derived from these buds was and measuring length of stomata vitro and the determined by ploidy of karyotyping of root cells (LIII layer) (LI layer). X-irradiation was used in vitro to obtain different morphological forms, dose rates of 3, 4 and 5 krads producing 68, 100 and 80% mutant forms respectively. It is suggested that the combined use of drug and X-ray treatments, use of GA^ and protoplast fusion in vitro would be appropriate subjects for further investigation.

The genomic variability of sixty-nine populations of the potato cyst nematodes (PCN) Globodera pallida and G. rostochiensis from Europe and South America were analyzed using the RAPD-PCR technique with sixty-six 10-mer primers. Large genomic differences were found between the two PCN species (i.e. 33%). The genomic pool of British G. pallida populations showed considerably less variation than the Peruvian populations, with 73% and 41% similarity between populations respectively. The genomic similarity among populations of G. rostochiensis was 89% for UK populations and 82% when the two continental European populations were included. Nevertheless, between populations within each species and from the same locality, genomic differences were still found. The RAPD-PCR technique proved to be useful for revealing the genomic variability between and within species using DNA extracted from 50 cysts, but it gave variable results when DNA extracted from individual females or cysts was used, suggesting that for evaluating the genomic variability of individuals it is better to use specific primers. RAPD-PCR was also used successfully to distinguish the two PCN species, individuals selected and selected for virulence and even biotypes using individual cysts. Based on the results found when comparing biotypes of Globodera pallida, it is suggested that all the biotypes considered in the International Pathotype Scheme could be grouped into Pa1 and Pa2/3 when classifying European populations, and Pa1A or Pa1B, P4A, P5A and P6A when analyzing South American populations. However, these groupings should be regarded just as a reference, because virulence bioassay results plus the data found using the RAPD-PCR technique suggested that, at least in G. pallida, virulence seems to be a polygenic trait ruled by several genes with additive effects. On the other hand, based on the same sort of data, virulence in G. rostochiensis seems to be ruled only by major genes. Selected and unselected populations of G. pallida, reared on either potato clone Solanum vernei (VTn)2 62.33.3 or a susceptible control, were distinguished using the RAPD-PCR technique and primers Operon A-07, E-06, G-16 and I-05. Three of the fragments that appeared to distinguish the unselected from the selected populations were cloned into an isolate of E. coli and their sequences obtained. Gpalpha, seems to be part of a promoter region of a gene probably related or linked to virulence. The use of differential clones to characterize PCN populations with different proportions of each virulence gene is a valuable tool. Whilst diagnostic probes for routine identification of virulent populations are being developed, the use of the “gene pool similarities” concept involving the DNA patterns of standard populations as genetic virulence types (i.e. virulence biotypes), integrated with information on their response to differential clones bearing genes for resistance, would represent the best approach towards devising a sustainable control strategy to optimize the usefulness of whatever resistance is available.

Plants are colonised by a vast amount of bacteria which are found in parts such as seeds, roots, leaves and fruits while fewer are found on blossoms, stems and vascular tissue. These different parts of plants make up distinct micro ecosystems which may result in different bacterial species (endophytes) colonizing these ecosystems. Such interactions could be for life or only a short period of time and may cause no significant damage or they could be latent pathogens. Isolations of both Gram negative and Gram positive bacteria have been made from an extensive range of plant species and include bacterial genera from the following groups: Firmicutes, Actinobacteria, á Proteobacteria, â Proteobacteria, and ã Proteobacteria. The focus of this study was the endophytic bacterial community of resistant, healthy and diseased Eucalyptus nitens clones, the latter of which showed symptoms of bacterial blight and die back previously described as caused by Pantoea ananatis. The endophytic bacteria of these sampled clones were studied using culturing dependent and independent methods. The focus was on the Enterobacteriaceae in order to determine whether P.ananatis is present as an endophyte of these clones. To obtain the isolates, standard culturing techniques were used, followed by sequence identification of the 16S rRNA as well as two housekeeping genes, rpoB and gyrB. Results obtained from the culturing study were compared to results obtained from a PCR-DGGE study of the same samples. Although no conclusion could be drawn as to which organism present caused the disease symptoms on the susceptible clones, it was seen that Enterobacter and Pantoea, were the most frequently isolated in both of the studies from all clones sampled. This implies that they are present as endophytes in the E.nitens clones, together with Pseudomonas and Bacillus as suggested by the DGGE study. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Microbiology and Plant Pathology / unrestricted

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.