Towards the characterisation of the raspberry root rot complex
Browne, E.Y. (2023) Towards the characterisation of the raspberry root rot complex. Doctoral thesis, Harper Adams University.
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Abstract
Raspberry root rot (RRR) caused by a consortium of oomycete species is an economically important disease of raspberries. Current management practices rely on an integrated program of chemical control via fungicides and cultural methods such as irrigation system sterilisation and planting resistant genotypes. The increasing deauthorization of fungicides with activity against Phytophthora species coupled with improving diagnostic technologies have prompted further research into the consortia of oomycete species involved in plant diseases like RRR. The aim of this study was to investigate the Phytophthora species present in the roots of plants exhibiting symptoms of root rot on nine commercial raspberry farms in the UK through traditional methods of isolation and molecular diagnostics such as lateral flow devices, polymerase chain reaction, and high throughput sequencing. Furthermore, the pathogenicity of the isolates obtained was assessed on a panel of commercially relevant raspberry varieties through detached leaf, root, and whole plant pathogenicity assays. Four isolates of the Phytophthora species P. citrophthora and one isolate of P. erythroseptica, P. cryptogea and P. pseudocryptogea were recovered from symptomatic raspberry roots via isolation. Six isolates of the Phytopythium species Pp. litorale and one isolate of Pp. vexans were also recovered, a first report of these species in raspberry and the UK. High throughput Illumina sequencing revealed 41 distinct sequences amplified across sites corresponding to nine Phytophthora species, four Globisporangium species, three Peronospora species and three Phytopythium species. P. rubi, P. cactorum, P. citrophthora, and P. bishii - a relatively new introduction to the UK, were detected in 100% of samples. Peronospora sparsa, the causal agent of downy mildew in roses, and P. rubi were the two species with the highest abundance across all samples. Farm location was the most significant factor affecting the diversity and abundance of the species detected. Subsequent pathogenicity testing on detached leaves and roots revealed plant genotype has a significant effect on the virulence of the isolates obtained in this study. The Phytopythium species Pp. litorale and Pp. vexans exhibited high and moderate pathogenicity on raspberry, resulting in fast-growing lesions on detached raspberry leaves and roots. Additionally, crown and root rot were observed in whole raspberry plants eight weeks after inoculation with zoospores of Pp. litorale and Pp. vexans. This study has demonstrated the diversity of Peronosporale species associated with RRR in the UK, adding to our understanding of the disease. Furthermore, two new pathogens of raspberry are presented which are targets for further research.
| Item Type: | Thesis (Doctoral) |
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| Divisions: | Agriculture and Environment (from 1.08.20) |
| Depositing User: | Mrs Terésa-Marie Brown |
| Date Deposited: | 15 Nov 2024 15:15 |
| Last Modified: | 15 Nov 2024 15:15 |
| URI: | https://hau.repository.guildhe.ac.uk/id/eprint/18147 |
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