The ecology and pathology of ash dieback disease

Combes, Matthew J. 2022. The ecology and pathology of ash dieback disease. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Ash dieback disease, caused by the ascomycete Hymenoscyphus fraxineus, emerged in Poland in the early 1990s and is currently causing mortality of Fraxinus excelsior throughout Europe. H. fraxineus is dependent on its sexual cycle for dispersal and host infection, but little is known about how environmental conditions affect these processes. Through laboratory and field experiments this thesis aims to understand the environmental effects on pathogen apothecia development on rachises (including the petiole) in the litter layer, ascospore ejection and germination, and subsequent host colonisation of rachises in the litter layer and its relationship to disease severity. Field studies revealed that temperature positively affected apothecia development, and this effect was greater at higher relative humidity and under sheltered litter layers, such as under vegetation, also associated with more open canopies. Laboratory studies uncovered the threshold for apothecia development was around 10°C and higher overwintering temperature increased the rate of subsequent apothecia development, but decreased the probability that they would develop. Ascospores were more likely to be ejected with increasing relative humidity and temperature, although the increase in ejection with increasing temperature was greater in areas with exposed litter layers. A greater density of ascospores was related to increased rachis colonisation by H. fraxineus, which was related to greater disease severity. Ascospores could germinate under a range of temperatures (5°C-30°C), but did not germinate at 35°C or -4.01 MPa (adjusted with KCl), and germination was greater in field collected rather than laboratory produced apothecia. A preliminary survey of F. excelsior trunk basal lesions detected both Armillaria gallica and Armillaria mellea, but trees with basal necrosis did not have more severe crown symptoms. Nascent management suggestions involve reduction of apothecia development and ascospore ejection by minimising moisture retention at tree bases, and prioritising surveys in sites with higher moisture in the litter layer.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Biosciences
Subjects:	Q Science > Q Science (General)
Date of First Compliant Deposit:	11 July 2022
Date of Acceptance:	11 July 2022
Last Modified:	10 Feb 2024 02:13
URI:	https://orca.cardiff.ac.uk/id/eprint/151199

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