The prevalence, detection and impact of root lesion nematodes (Pratylenchus spp.) found in potato growing land in Great Britain
Orlando, V. (2021) The prevalence, detection and impact of root lesion nematodes (Pratylenchus spp.) found in potato growing land in Great Britain. Doctoral thesis, Harper Adams University.
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Abstract
Potato (Solanum tuberosum) is one of the most important crops in the world and yield can be negatively influenced by several pests, including plant-parasitic nematodes. Few studies have been conducted on root-lesion nematodes (Pratylenchus spp.) and their impact on the potato production in Great Britain. The main objectives of this study were: (1) to identify Pratylenchus spp. present in potato growing land in England and Scotland, and to develop molecular assays for their rapid confirmation and quantification; (2) to undertake a survey to determine the distribution and prevalence of Pratylenchus spp. in potato growing land in England and Scotland; (3) to determine pathogenicity and potato damage thresholds for Pratylenchus species in different soil types with Maris Peer cultivar, under controlled conditions. Accurate identification and quantification of root-lesion nematodes (Pratylenchus spp.) is an important step for nematode management. Molecular diagnostics may provide an alternative to morphological identification that is time consuming and requires significant taxonomic experience. Efficient DNA extraction is the first important step for any molecular diagnostic. Six common DNA extraction protocols were compared to evaluate their efficiency to obtain quality DNA samples for Pratylenchus penetrans. Among all methods tested, the DNA extraction protocol with glass beads proved to be efficient for P. penetrans and it was selected to be tested for other Pratylenchus species (P. crenatus, P. neglectus and P. thornei). The method generated high quality DNA for molecular analysis, and it was used for the development of real-time quantitative PCR (qPCR). A TaqMan hydrolysis probe assay based on 28S rDNA D2-D3 expansion fragment was developed and validated for the identification and quantification of P. crenatus, P. neglectus, P. penetrans and P. thornei. Four standard curves were made showing a strong linear correlation (R2 = 0.99) between Ct values and DNA copy numbers with no cross reaction with non-target species, demonstrating the specificity of primers and probes. Specificity, sensitivity and selectivity of the methods were confirmed also by three further experiments with different life stages, increasing numbers of target species and mixed samples. Finally, estimates obtained by qPCR methods were compared with counting done by microscopy showing a good correlation (R2 = 0.78). The qPCR TaqMan assays here developed were specific, sensitive, fast and accurate for quantification of P. crenatus, P. neglectus, P. penetrans and P. thornei. Little is known regarding the presence and distribution of Pratylenchus spp. in potato fields in Great Britain. Two hundred potato fields from the top fifteen counties in England with highest area of potato production were sampled between September and November, in 2017 and 2019. Samples from eighteen fields in Scotland were examined in a separate study. Rootlesion nematodes were detected in 88% of soil samples from England and 94% from Scotland, 8 revealing a high presence in agricultural land in both countries. Positive detections were higher in the East and North East of England, with Pratylenchus neglectus and P. thornei being the most widely distributed species in England; P. crenatus and P. penetrans were also detected but were less abundant. Pratylenchus thornei was the most abundant species in South East and South West England, P. neglectus was mainly found in the East and P. penetrans in North East and South East of England. Biotic factors that may influence the presence and prevalence of each species such as soil type, previous crop, crop at sampling, irrigation, nematicide application did not have significant effects on the presence and abundance of the genus as a whole or the individual species. In Scotland, the most present and abundant species were represented by P. neglectus and P. crenatus, but also P. penetrans and P. thornei were recorded. Three controlled environment experiments investigated the impact of P. penetrans and P. thornei on the yield and quality loss of the Maris Peer potato variety. The first experiment assessed the impact of mixed juveniles and adult populations of P. penetrans, ranging from 0.125 to 4 nematodes g-1 soil, on growth and yield of Maris Peer. Different proportions of coarse sand and compost (John Innes No. 2) were mixed to form three different sandy based soils: ST1 (10% compost and 90% coarse sand), ST2 (20% compost and 80% coarse sand) and ST3 (40% compost and 60% coarse sand). Nematode density had no effect on potato yield at six weeks after inoculation and planting, although the yield was significantly affected by soil type with ST1 giving the lowest yield. Root-lesion nematodes were detected within the roots of potatoes grown in each soil type, highlighting that P. penetrans was able to infect this cultivar without inducing yield loss at these population densities. Two further controlled experiments using a broader range of nematode densities, from 2 to 32 nematode g-1 soil were conducted with P. penetrans and P. thornei, respectively. As with the first experiment, the nematode densities investigated were found to have no effects on potato yield, but both species were detected within the roots of potatoes, confirming invasion occurred. Final population density (Pf) were less than the initial population density (Pi) in all treatments and experiments, suggesting that reproduction was limited on Maris Peer and may indicate partial resistance by this cultivar. However, the length of experiment and other factors such as temperature, moisture or soil matrix under pot trials may have influenced the reproduction of nematodes. Further studies using other GB potato cultivars, other common root-lesion nematode species like P. neglectus or P. crenatus, considering also stress factors such as drought conditions, may help provide a better understanding of the nematode’s pathogenicity and impact on yield in GB potato cultivars. Consequently, further strategies may be considered for root-lesion nematode management to help farmers to limit the potential impact of these nematodes on potato production
| Item Type: | Thesis (Doctoral) |
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| Divisions: | Agriculture and Environment (from 1.08.20) |
| Depositing User: | Ms Kath Osborn |
| Date Deposited: | 02 Mar 2022 11:51 |
| Last Modified: | 02 Mar 2022 11:53 |
| URI: | https://hau.repository.guildhe.ac.uk/id/eprint/17815 |
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