An epidemic increase in severity and incidence of asochyta blight, caused by Ascochyta rabiei (Pass) Labrousse (teleomorph: <i>Didymella rabiei</i> (Kovachevski) v. Arx. Syn. <i>Mycosphaerella rabiei </i>Kovachevski), has occurred on chickpea (<i>Cicer arietinum</i> L.) crops in Saskatchewan over the past 5 growing seasons. In order to explore the nature of the outbreak, studies assessing population differences in pathogenicity and genetic variability were employed. Isolates of <i>A. rabiei</i> collected in 1998, 2001 and 2002 were inoculated onto 7 differential chickpea genotypes for pathogenicity testing. <p> Significant isolate by differential interaction occurred, but accounted for a low proportion of the total variability suggesting no genotype specific relationship exists between <i>A. rabiei</i> and <i>C. arietinum</i>. Furthermore, it was found that when averaged over all differentials, the isolates from 2001 and 2002 caused significantly greater disease than isolates from 1998, suggesting that the disease epidemic is in part due to a shift in the population to overall greater aggressiveness. The largest increase in disease severity was observed on the cultivar Sanford, which was widely grown in commercial chickpea fields before 1999. To evaluate the genetic diversity of different <i>A. rabiei</i> populations, 30 isolates from 1998 and 30 isolates from 2002 were compared with random amplified polymorphic DNA fingerprinting. Several clusters of isolates collected from either 1998 or 2002 were approximately 60% genetic similar suggesting divergence of these populations of <i>A. rabiei</i>. However, analysis of molecular variance showed that over 90% of the variation occurred within populations. Pairwise differences and gene diversity over loci showed that genetic diversity of the 2 populations had the same amount of genetic variability. Analysis of mating type distributions revealed that the populations from 1998, 2001 and 2002 did not significantly depart from a 1:1 ratio suggesting random mating of each population. Further supporting the hypothesis of a randomly mating population, linkage disequilibrium for both 1998 and 2002 populations was very low.
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-05032005-212624 |
| Date | 09 May 2005 |
| Creators | Vail, Sally L |
| Contributors | Warkentin, Tom D., Scoles, Graham, Kutcher, Randy, Hughes, Geoffrey R., Banniza, Sabine |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-05032005-212624/ |
| 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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