Soil-borne pathogens of oilseed rape: assessing their distribution and potential contribution to yield decline
McCormack, A. (2019) Soil-borne pathogens of oilseed rape: assessing their distribution and potential contribution to yield decline. Doctoral thesis, Harper Adams University.
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Abstract
Yield decline of oilseed rape(OSR)is a complex and multifaceted problem, with many contributing components. This is further compounded by soil-borne pathogens which are becoming an increasing concern, with shortened and species poor rotations implicated in their increase in recent decades. As a consequence,this thesis aimed to utilise molecular techniques to observe for pathogenic species within commercial crops of OSR, relating their occurrence to possible agronomic factors, whilst elucidating their role in yield decline through glasshouse experiments. Chapter 3utilisedreal-time PCR(qPCR)to examine the occurrence of Rhizoctonia solani, Pythium ultimum and Gibellulopsis nigrescens. However this proved difficult as many of the assays available were not well designed or validated. Instead high throughput sequencing was utilised in Chapter 4to examine the fungal communities within OSR roots, aiming to elucidate any pathogenic species present, along with their relation to potential agronomic factors. From this it was found that fungal communities were relatively simple, comprising of a few main phyla, genera and species; although this varied drastically with analysis technique used. Similarly, no relationship was observed between these species and the agronomic factors associated with the samples. However, both techniques used suggested that R. solaniwas a prominent pathogen within all of the samples, and as such warranted further study. Rhizoctonia solaniis a diverse and variable pathogen comprising of 13 known sub-groups or anastomosis groups (AG), with Chapter 5 aiming to characterise these utilising AG specific qPCR assays. From this it was found that AG 2-1 was the main AG present within the samples, followed by AG 8 and 5. This was also confirmed by pathogenicity testing of UK isolates in chapter 6, where only AG 2-1 caused significant disease on OSR seedlings. Glasshouse experiments examined the role of pathogen inoculum in causing disease, and to clarify the mechanism by which yield loss occurred. Whilst the results varied between experiments as a consequence of inoculum preparation, they suggested that no sub-clinical disease symptoms occurred at the doses tested. In addition to this, the mechanism of yield loss appeared to be restricted to pre-and post-emergence damping off of seedlings which impacted on plant emergence and stand evenness. Further experiments in Chapter 6 examined the variability in a collection of UK isolates comprising primarily of AG 2-1 and other OSRnon-pathogenic AG. Utilising an in vitropathogenicity test it was found that AG 2-1 resulted in the most severe disease followed by AG 8 and4further supporting the qPCR results in Chapter 5 and the literature; although this was limited by the number of isolates. Interestingly,variation also existed within the AG 2-1 isolates with some being non-pathogenic in this system.In conclusion, from this work it is apparent that soil-borne pathogens are present within UK crops of OSR, being present at levels which may impact on plant emergence and thus yield. However there is still a considerable way to go before effective management practices can be implemented by growers, with this being apparent from the lack of correlation between agronomic factors and the presence of R. solaniAG 2-1. In addition this may also be further compounded by genetic and pathogenic variation in UK populations of AG 2-1,but this requiresfurther study.
| Item Type: | Thesis (Doctoral) |
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| Divisions: | Crop and Environment Sciences (to 31.07.20) |
| Depositing User: | Ms Kath Osborn |
| Date Deposited: | 10 Apr 2019 15:29 |
| Last Modified: | 03 Jun 2019 08:36 |
| URI: | https://hau.repository.guildhe.ac.uk/id/eprint/17397 |
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