<i>Pyrenophora teres</i> Drechs. (anamorph: <i>Drechslera teres</i> (Sacc.) Shoem.) is the causal agent of barley net blotch. Net blotch is an economically important disease commonly found throughout the barley producing regions of the world. Significant financial losses result from yield reductions, ranging from 15-35%, and decreased grain quality. Despite its prevalence, it is unclear if the P. teres-barley pathosystem follows a gene-for-gene model, and more generally, little is known about its genetic organization. Three studies were initiated to address these questions.<p>The first study investigated the genetic control of avirulence in <i>P. teres.</i> To establish an appropriate study system, a collection of ten net form (<i>P. teres f. teres</i>) and spot form (<i>P. teres f. maculata</i>) isolates were evaluated on a set of eight differential barley lines to identify two isolates with differential virulence on a specific host line. WRS 1906, exhibiting low virulence on the cultivar Heartland, and WRS 1607, exhibiting high virulence, were mated and 67 progeny were isolated and phenotyped for virulence on Heartland. The population segregated in a 1:1 ratio, 34 avirulent to 33 virulent (Chi-square = 0.0, P = 1.0), indicating single gene control of WRS 1906 avirulence on Heartland. Bulked segregant analysis was used to identify six amplified fragment length polymorphism (AFLP) markers closely linked to the avirulence gene (AvrHeartland). This work provides evidence that the P. teres-barley pathosystem conforms to the gene-for-gene model.<p>In the second study, five isolates of P. teres, representing both net and spot forms, were analyzed by the germ tube burst method (GTBM) and pulsed field gel electrophoresis (PFGE) to determine the species karyotype. Nine chromosomes were observed in all isolates using the GTBM and estimation of chromosome lengths varied from 0.5 to 3.0 µm. PFGE separated 7 to 8 bands depending on isolate, but analysis of bands by densitometry indicated nine chromosomes. Chromosome size ranged from 1.8 to ~6.0 Mb providing a genome size estimate of 32 to 39 Mb. Significant chromosome-length polymorphisms (CLP) were observed between isolates. These CLP did not hinder mating between mating-type compatible net form isolates. No particular CLP or individual chromosome could be associated with differences in disease symptoms observed between pathogen forms. This study provides the first karyotype of both P. teres forms and will assist genetic mapping of this pathogen.<p>A genetic linkage map of <i>P. teres f. teres</i>, was constructed in the third study using the population of 67 progeny derived from the WRS 1906 WRS 1607 cross. The map consists of 138 markers including 114 AFLPs, 21 telomere RFLPs, the mating-type (MAT) locus and an avirulence locus (AvrHeartland) controlling interaction with barley cultivar Heartland. Markers were distributed across 24 linkage groups ranging in length from 2 to 110 cM with an average marker interval of 8.5 cM. The total map length was 797 cM. A telomere-specific probe, consisting of the sequence (TTAGGC)4, was used to map 15 of the 18 telomeres. One of these telomeres mapped to within 3 cM of the AvrHeartland locus. Attempts to consolidate linkage groups by hybridizing markers to the electrophoretically separated chromosomes was unsuccessful because probes bound to multiple chromosomes, likely due to repetitive DNA within the probe. This is the first genetic map reported for this species and it will be a useful genetic tool for map-based cloning of the AvrHeartland gene tagged in this study. <p>This research has provided a number of new insights into the net blotch pathogen and provides a useful research tool in the form of a genetic map. This information lays the foundation for further genetic study of P. teres and will complement studies on barley resistance to net blotch that may potentially lead to more durable resistance.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:SSU.etd-10312006-113605 |
| Date | 31 October 2006 |
| Creators | Beattie, Aaron David |
| Contributors | Wei, Yangdou, Steffenson, Brian, Scoles, Graham, Rossnagel, Brian G., Coulman, Bruce E., Banniza, Sabine |
| Publisher | University of Saskatchewan |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-10312006-113605/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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