The current investigation used multiple cultivars of potato and genotypes of Phytophthora infestans to study the P. infestans genotype x cultivar interaction, and investigat~ the influence of competition and level of field resistance on selection within the late blight population. Multiple genotypes ofP. infestans from the local populations in Northern Ireland (UK) and the state of Michigan (US) were inoculated onto separate field trials planted in 2003, 2004 and 2005. Single-lesion isolates were collected from leaves when plots reached 1% infection, characterized 'using pre-assigned markers and re-assigned to t~eir respective genotypes. Extreme selection occurred within the populations of genotypes of P. infestans at . both locations in each year. In Northern Ireland, the effect of the potato cultivar was clear with different genotypes dominating infection of different cultivars. Selection was greatest on the more resistant cultivars, but the effect was observed on all cultivars tested. By contrast, in Michigan, the US-8 genotype dominated infection of all cultivars and only rarely were other genotypes detected. Each genotype was assessed for relative aggressiveness on potato cultivars from field trials by measuring infection frequency, latent period and lesion size 5 and 7 days after inoculation. Of the N. Ireland genotypes, those dominating infection of more resistant cultivars in field trials were also more aggressive by lesion expansion. However this was not true on the susceptibJe cultivars. Of the Michigan genotypes, US-8 was significantly the most aggressive, which probably explains the dominance of this genotype in field trialS and in populations from the US in general. Genotypes from N. Ireland were further studied by comparing competitive ability in the laboratory, through use of a combined inoculum experiment using detached leaflets of cultivars used in field trials. Extreme selection occurred on all cultivars but this was different from that observed in field trials.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:486250 |
| Date | January 2008 |
| Creators | Young, Gillian Kathleen |
| Publisher | Queen's University Belfast |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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