Characterisation of potato cyst nematodepopulations in Great Britain for sustainable crop management
Dybal, K. (2020) Characterisation of potato cyst nematodepopulations in Great Britain for sustainable crop management. Doctoral thesis, Harper Adams University.
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Abstract
Potato cyst nematodes (PCN), comprised of two related species (Globodera rostochiensisand G. pallida), are the most destructive pests of potato crops in Great Britain (GB) and other temperate regions. It is estimated that PCN are the second, after late blight, greatest cause of losses in potential yield and quality worth nearly £26 million per year.Development of potato genotypes with the H1resistance gene proved to be highly effective in controlling G. rostochiensisbut at the same time increased the risk of selection of G. pallida. The management of the latter is expensive and more challenging due to the pressure to replace chemical control products and the lack of potato genotypes fully resistant. In the most recent survey G. pallidawas identified as being the dominant species and present in approximately 92% of the infested potato fields, which indicated that the species distribution of PCN has been changing.To fully understand a possible infestation level, the assessment of PCN population densities should include a measurement of the viability of the eggs. The absence of a precise viability assessment might lead to inaccurate determination of field populations and inappropriate selection of management strategies. At the moment viability tests are not often commercially performed as they are still too expensive and time consuming to be widely accessible for the growers. Although, the complexity of PCN virulence is not well defined by the methodology used in the pathotype scheme from 1977, which includes a limited selection of resistance genes and lacks an important genotype currently used in potato breeding programs, the ideology used to develop this scheme is still in use. This makes the search for markers that can be used to monitor populations even more important. Recently, certain populations of G. pallidawere found to contain mixtures of genotypes, which are likely to represent three distinct geographical introductions from the Andes. These haplotypes were renamed as mitotypes. This novel method provides an efficient way to assess the complexity of field populations by investigating occurrence of partial sequence of cytochrome bgene descriptive of these introductions.Understanding PCN population’s characteristics is of paramount importance to the selection of appropriate management methods and to indicate the direction of the future research. This study aimed to characterise current PCN populations by conducting a PCN survey of ware potato growing land in GB. Collected survey samples were further investigated to provide up-to-date information about the regional prevalence of PCN, the ratio between PCN species, the virulence and mitotype composition of selected populations and the viability determined using a test validated as suitable for field samples of G. pallidapopulations.The results identified a decrease in the incidence of PCN (48%)compared with the previous survey and confirmed the continuous shift towards G. pallidaas the predominant species. Of populations found to be PCN infested, 89% were G. pallida, 5% were G. rostochiensisand 6% contained both species. Viability testing by hatching in potato root diffusate assay did not take into account the viability of the unhatched, possibly dormant, eggs and should not be used as the sole indication of field population density. Assessment of G. pallidapopulations using techniques based on staining with Meldola’s blue overestimated the number of viable eggs in heat-treated samples. The trehalose assay was proven to be a good alternative to the other methods. Globodera pallidafield population’s virulence assessment showed that potato genotypes with resistance derived from S. verneicontrolled reproduction better than when derived from S. tuberosumspp. andigenaCPC2802. Genotype with resistance derived from S. multidissectumPH1366 showed partial resistance to all of the field populations. This indicates that using these three genotypes in the field has potential to effectively reduce G. pallidainfestations.Finally, next generation sequencing revealed that mitotype 2 was not present in any of the G. pallidafield populations from England. All tested populations were found to be mitotype 1, mitotype 3 and a mixture of mitotypes 1 and 3
| Item Type: | Thesis (Doctoral) |
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| Divisions: | Crop and Environment Sciences (to 31.07.20) |
| Depositing User: | Ms Kath Osborn |
| Date Deposited: | 05 Mar 2021 11:43 |
| Last Modified: | 05 Mar 2021 11:43 |
| URI: | https://hau.repository.guildhe.ac.uk/id/eprint/17659 |
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