Thesis (Ph. D.)--Murdoch University, 2007. / Thesis submitted to the Faculty of Sustainability, Environmental and Life Sciences. Includes bibliographical references (leaves 147-172).

Made available in DSpace on 2014-06-11T19:28:37Z (GMT). No. of bitstreams: 0 Previous issue date: 2004-06-25Bitstream added on 2014-06-13T20:58:39Z : No. of bitstreams: 1 boava_lp_me_botfca.pdf: 497651 bytes, checksum: 37f114f566262afe532ca550bf9ecb9f (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Universidade Estadual Paulista (UNESP) / Phytophthora parasitica, principal causador da gomose dos citros, é um importante patógeno dos citros provocando danos em viveiros e no campo. Programas de melhoramento visando obtenção de plantas resistentes a P. parasitica exigem informações detalhadas sobre o tipo de herança e a localização de genes de resistência no genoma. Fontes de resistência às doenças podem ser encontradas em gêneros correlatos a citros como Poncirus sp. O presente estudo teve como objetivos detectar e verificar a estabilidade de marcadores moleculares e locos controladores de características quantitativas (QTLs) ligados à resistência a gomose em uma progênie F1 obtida do cruzamento entre Citrus sunki vs. Poncirus trifoliata 'Rubidoux'. As avaliações fenotípicas de três conjuntos de dados de 3 épocas de avaliação distintas foram incorporadas às informações dos mapas de ligação estabelecidos através de marcadores moleculares do tipo RAPD. Plantas jovens foram inoculadas com o patógeno, usando o método do disco e avaliadas medindo-se o comprimento da lesão. A estratégia do 'pseudo-testcross' foi adotada como delineamento genético. Os QTLs foram mapeados utilizando o método do mapeamento por intervalo composto (CIM) com o programa QTLCartographer v.1.25. A partir das média de todos os experimentos, foram identificadas 5 posições nos grupos de ligação II, III e V de P. trifoliata associadas à gomose de Phytophthora. Em 2 posições observou-se uma correlação na detecção de QTLs para as avaliações realizadas em duas das três épocas. Demonstrado desta forma a ocorrência da interação genótipo ambiente. / P. parasitica, is the most important main causal agent of Citrus Phytophthora gummosis in Brazil and hve caused damage in nurseries and orchards. Improving resistence programs to get resistant to P. parasitica have been detailed information about the inheritance and gene localization resistance. Source of disease resistance can be found in correlated genera like Poncirus trifoliata. The present study had the objective of detecting molecular markers associated to quantitative trait loci (QTL) for resistance to Citrus Phytophthora gummosis using F1 lineage obtained between Citrus sunki vs. Poncirus trifoliata 'Rubidoux' cross. Phenotypical evaluations will be incorporated in linkage maps established through RAPD molecular markers. Young plants were inoculated with P. parasitica, using the disc method and evaluated after one month measuring lesions length. Pseudo-testcross strategy was be used for genetic outlining. All this information were evaluated in specific genetic-statistical programs. QTLs were mapped using the method of the maps for composed interval (CIM) with the program QTLCartographer v.1.25. CIM. Starting from the average of all of the experiments, they were identified 2 positions in the group of connection II of P. trifoliata associated with gomose of Phytophthora. In each area a correlation was observed in the detection of QTLs for the evaluations accomplished in two of the three times... (Complete abstract, click electronic address below).

Late Blight disease, caused by Phytophthora infestans, is the most significant threat to potato production world-wide. Identifying and deploying more durable host resistance to P. infestans is a promising way forward to sustain the production of potato. To achieve this goal, it is important to seek key pathogen components that are essential for infection and which, upon detection by the host, trigger a resistance response. One such potential key pathogen molecule is the RXLR-containing effector Avr3a. Avr3a is highly up-regulated during infection and is also required for P. infestans pathogenicity. To date, all P. infestans isolates studied contain Avr3a alleles E80M103 and/or K80I103. However, a study of Avr3a diversity in the Toluca Valley, Mexico, has identified additional alleles such as K80I103L139, K80I103H133, E80M103H133 and E80M103G124. Functional studies of these alleles were conducted as part of this thesis, which also include the Avr3a paralogs Pex147-2 and Pex147-3. By examining the amino acid changes in relation to the established protein structure, it was determined that all alterations within the Avr3a variants occur at surface exposed amino acids. The change R124G that leads to Avr3aEMG is located in the a-helix loop 3 and the changes Q133H and M139L (Avr3aKIH, Avr3aEMH and Avr3aKIL) locate to a helix 4. Whereas amino acid substitutions in PEX147-3 only affect surface exposed residues, amino acid changes that occur in PEX147-2 involves a ‘buried’ amino acid that is key to structure and stability. Indeed, with the exception of PEX147-2, all Avr3a variants and PEX147-3 are stable upon transient expression in planta and in yeast cells. In terms of host recognition, the protein products of the Avr3a alleles derived from Avr3aKI are recognised by the cognate host resistance gene product R3a whereas those derived from Avr3aEM evade recognition. Similarly, PEX147-3 is recognised by R3a but PEX147-2 is not. In addition to host recognition, virulence functions of these alleles and paralogs have been elucidated. INF1 and AVR4/CF-4 induced cell death responses, which are dependent on the host defence protein CMPG1, are suppressed by Avr3aKI, Avr3aKIH, Avr3aKIL, Avr3aEM and Avr3aEMG but not by Avr3aEMH. All Avr3a variants interact with and stabilise the host E3 ubiquitin ligase CMPG1 to various degrees in planta and this interaction was found to be weakest for Avr3aEMH. Interestingly, PEX147-3, which did not interact with or stabilise CMPG1, could only suppress INF1 cell death but not CF-4/AVR4 elicited responses. A P. infestans isolate, CS12, which was stably silenced for Avr3aEM expression and subsequently shown to be compromised in virulence on the normally susceptible host Nicotiana benthamiana, was used for in planta complementation studies. As shown previously, upon transient expression in planta prior to infection with C12, Avr3aKI and Avr3aEM successfully restore pathogenicity. Similar levels of virulence re-establishment were only observed for Avr3KI derived alleles Avr3aKIH and Avr3aKIL but not for alleles derived from Avr3aEM. This study concludes that Avr3aEM is currently the only form of the essential effector that is fully functional and evades recognition by the known resistance gene product R3a. This functionality is the likely reason that 70% of all studied isolates in the Toluca Valley are homozygous for Avr3aEM. This form of the effector is therefore a suitable target for identifying more durable resistances.

Bibliography: leaves 158-189. / x, 189 leaves : ill. (some col.) ; 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 Crop Protection, 1994

Bibliography: leaves 158-189.

Oomycetes, like fungi, are filamentous heterotrophs, but unlike true fungi are diploid and share a photosynthetic ancestor. Many of these organisms are plant and animal pathogens, and members of the genus Phytophthora cause devastating disease on a diverse array of agricultural plant hosts. Several diverse topics in oomycete biology are investigated in this dissertation. Chapter 2 is a report on loss of heterozygosity in Phytophthora capsici in response to chemical mutagenesis.The research presented in Chapters 3 and 4 are centered on documenting biodiversity and genetic diversity of populations of Phytophthora species obtained from infected plant hosts. The final chapter (Chapter 5) involves determining genetic diversity, ecology, and enzymatic activities of Pythiaceous oomycetes from marsh wetlands of the southeastern US.

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This thesis is concerned with an analysis of swimming of oomycete zoospores, particularly in relation to the hypothesis that electrotaxis mediated host root colonisation. A correlation was found between the electrotactic behaviour of zoospores of <I>Phytophthora palmivora </I>and <I>Pythium aphanidermatum</I> and their localisation relative to anodic or cathodic regions of the majority of non-host roots. Cathodotropic <I>P. aphanidermatum </I>zoospores were found to be attracted to the cathode generated at the wound site on monocotyledonous and dicotyledonous plant roots studied. Zoospores of <I>P. aphanidermatum</I> were also found to become gradually less attracted to these wound sites as they dissipated over time. Anodotropic <I>P. palmivora </I>zoospores were found to be repelled by the cathodic wound sites on roots of all plants investigated, with the exception of <I>Petunia hybrida. </I>In addition to this zoospores of <I>P. aphanidermatum</I> were found not exhibit chemotaxis or encystment in gradients of the wound-specific metabolite acetosyringone. This suggests that electrotaxis and chemotaxis both operate in directing zoospore accumulation around roots. This reduction of the conductivity of the bathing medium by the addition of different concentrations of sodium chloride salts did not appear to affect the accumulation of both zoospore species around roots of rye grass. The results of this study supports the hypothesis that zoospores use electrotaxis as one means to locate new plant hosts in the rhizosphere. However, chemotaxis may still augment the regulation of zoospore colonisation and encystment.

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1984. / Bibliography: leaves [82]-88. / Photocopy. / Microfilm. / viii, 88 leaves, bound ill. 29 cm