Many plants produce toxic compounds, called phytoalexins, in response to infection by microorganisms. Some fungal pathogens of these plants can detoxify their host's phytoalexins and genetic studies of the ascomycete, Nectria haematococca Mating Population VI have established an association between detoxification of the pea phytoalexin, pisatin (Pda), and pathogenicity. Previous studies of one of the six genes (PDA) that confer this trait (PDA6-1) was on a dispensable chromosome. In the current study, a technique was developed that uses the pea plant to select for highly virulent recombinant progeny from crosses in which such progeny were relatively rare. It was demonstrated that when pea plants are inoculated with a mixture of ascospores that isolates recovered from pea lesions showed a strong bias for Pda and for being more virulent on pea, compared with ascospore progeny which did not undergo selection on plant. Additionally, all highly virulent isolates had PDA1-1, one of the three PDA genes present in the cross parents, showing that PDA1-1, or a linked gene, was necessary for virulence on pea. In the current study, highly virulent isolates were also identified by screening progeny from crosses that involved a highly virulent parent, 34-18. Analysis of 34-18 and its progeny showed that this isolate contains three PDA genes, PDA5 and PDA9, which were characterized in this study, and an allele of a previously characterized PDA gene. All three genes were associated with virulence on pea and could be lost during genetic crosses. Electrophoretic karyotype (CHEF) analysis showed that this was due to loss of a 1.5 Megabase chromosome carrying PDA1-2 and at least a portion of a 4.9 Mb chromosome carrying PDA5 and PDA9. CHEF analysis also showed that the other previously characterized PDA genes (PDA1-1, PDA2, PDA3, PDA4, PDA6-1 and PDA6-2) were on dispensable chromosomes. These dispensable chromosomes were not required for pathogenicity on carrot and ripe tomato. The results from this work provide evidence to support the hypothesis that the PDA chromosomes are dispensable, that some of them contain genes conferring virulence specifically on pea and genes for pathogenicity on other hosts were on non-PDA chromosomes.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/288699 |
| Date | January 1996 |
| Creators | Funnell, Deanna Lillian |
| Contributors | VanEtten, Hans D. |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Dissertation-Reproduction (electronic) |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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