Molecular evolution of fungicide resistance in Blumeria graminis

Arnold, Corinne (2018) Molecular evolution of fungicide resistance in Blumeria graminis. Doctoral thesis, University of East Anglia.

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Blumeria graminis, a powdery mildew pathogen which infects many wild grasses and cereals across the world, can cause significant losses in cereals. Applying fungicides is a main method for control, but resistance to quinone outside inhibitors and many triazole fungicides already occurs in B. graminis, and few other effective fungicides are available.

In this thesis, isolates were characterised from an outbreak of B. graminis f. sp. tritici (Bgt) on wheat where three major fungicides had lost effectiveness: cyflufenamid (Cyflamid), fenpropimorph (Corbel), and prothioconazole (Proline). All isolates from the study site were completely resistant to cyflufenamid at the recommended field rate. Additionally, isolates sampled following two sprays of fenpropimorph, had significantly lower sensitivity than field isolates.

RNA sequencing was used to identify the spindle assembly checkpoint protein MAD1 as a candidate target of cyflufenamid, implying that the mode of action of cyflufenamid may be to inhibit mitosis. A candidate mutation in MAD1 causing cyflufenamid resistance was also discovered. Sequencing the Erg24 gene in isolates sensitive or resistant to fenpropimorph identified a mutation that may confer resistance in Bgt, which was subsequently confirmed by site-directed mutagenesis of yeast, and a different Erg24 mutation was found in B. graminis f. sp. hordei, the barley mildew pathogen. Multiple copies of the Cyp51 (Erg11) gene were identified in Bgt isolates. Some isolates with elevated resistance were heteroallelic, carrying both wild-type and mutant Cyp51 genes. Triazole-resistant isolates had greater expression of Cyp51 than more sensitive isolates, as did UK isolates compared to those from the USA.

In summary, this thesis updates knowledge of resistance to currently available fungicides and their modes of action against powdery mildew. This is important in helping to reveal how resistance to fungicides occurs. In turn, this knowledge can contribute to the discovery of new fungicides and to using new and existing chemicals more effectively.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Users 9280 not found.
Date Deposited: 13 Jun 2019 11:01
Last Modified: 30 Sep 2019 00:38

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