Persistence and hatching characteristics of potato cyst nematode populations and the implications for sustainable management
Prof P Urwin (SoB), Dr K. Field (SoB), Dr A. Barker (CASE Supervisor - Barworth Agriculture)Project partner(s): Barworth Agriculture Ltd.(CASE)Contact email: firstname.lastname@example.org
This is a CASE project in collaboration with Barworth Agriculture, a small agricultural and horticultural R & D company based in Lincolnshire. They have extensive experience of field experiments involving a range of crops and the student will work with them to collect and analyse soil and nematode samples from field sites around the UK. The student will also have the opportunity to get involved with Barworth’s other strategic research projects for a wider experience of science in the commercial sector.
The potato cyst nematodes (PCNs) Globodera rostochiensis and G. pallida, commonly known as eel worms, are important soil pests that cause major economic losses to potato growers. Globodera pallida is the most prevalent species in the UK and its control is the most problematic. A lack of commercially favoured resistant potato varieties and concerns surrounding the use of chemical control measures have resulted in G. pallida being an intractable problem to farmers both in the UK and in many other countries.
PCN lives as a parasite and must complete the majority of its life-cycle in potato roots. The infective J2 larval stages hatch from cysts in the soil and migrate towards the host root which they penetrate. Inside the root, they set up specialised feeding sites, become sedentary and undergo their reproductive cycle with the body wall of the dead female forming a tough cyst, in which the eggs are retained. Like other specialized parasites, the life cycle of PCN is synchronized with that of its host to optimize the chances of success. This synchrony is possible because PCN unhatched juveniles can remain dormant until a stimulus from a suitable host is perceived, indicating favourable conditions for hatching. Some eggs will only hatch on restimulation; a strategy to increase population persistence over growing seasons and to lower competition between hatched larvae. As a result, this survival stage exhibits remarkable longevity, with dormant J2 larvae remaining viable for more than 20 years. Such resistant stages are extremely problematic in an agricultural context. The ability to persist in the soil in the absence of a host contributes significantly to the economic importance of cyst nematodes.
Hatch rate in response to host stimulus, extent of spontaneous hatch in the absence of a host and persistence/prolonged viability of the dormant nematode stages are influenced by a number of external environmental factors as well as genetic characteristics of particular populations. Whilst these hatch-related attributes impact current management practices, they could also be the target of novel control strategies.
This project will determine the environmental and genetic factors that influence hatching and population decline rates of potato cyst nematode and explore the potential for manipulating the hatch response via the host plant.
Objective 1. Quantify and model PCN decline rates, identify persistent populations and determine if there is a genetic link
The field decline rate of PCN between potato crops is mainly associated with spontaneous hatch in years when no host is planted. Decline rates depend on factors such as soil temperature and type, but also vary with the persistence characteristics of the PCN population. Soil samples will be collected from PCN-infested fields around the UK. Cysts will be extracted and the decline rate calculated from assessment of size, viable egg content and time elapsed since last potato crop. Any correlation between decline rates and soil type/recorded soil temperatures/cropping history will be determined. Cysts of selected PCN populations covering a spectrum of persistence will be maintained in different soil types and conditions and periodic sampling and analysis will allow populations with robust high persistence to be identified.
Genetically distinct populations of G. pallida have been characterised in the UK. A metagenetic approach, using next-generation sequencing of targeted genes, will be taken to analyse PCN populations studied in this work to determine if there is any correlation between particular genetic types and decline rates.
Objective 2. Determine if selection for delayed hatch underlies apparent increased field resistance to pesticides.
Differences in host-stimulated hatch rate of nematodes may influence the efficacy of pesticide soil treatment. Apparent increased field resistance to pesticides in some locations may be linked to selection of populations with delayed hatch response, such that most hatched larvae are present in the soil after the pesticide concentration has fallen to an ineffective level. To test this, cysts of suspected “resistant” populations and unselected “susceptible” controls, will be stimulated to hatch and the rate determined. Together with experiments to assess the direct effects of pesticides on nematodes of each population, this will help to elucidate the underlying basis for the reduced field efficacy of chemical control.
Objective 3. Explore how the host plant can be used to manipulate hatching of PCN.
A chemical produced by potato plants has been isolated as a ‘hatching factor’ that specifically stimulates hatch of PCN. The potential biosynthetic pathways of this compound have been identified. As PCN have an absolute requirement for host root exudates to stimulate hatch, knocking-out the function of one or more of the biosynthetic genes in potato plants could cause a failure of hatch in the field and be of enormous commercial benefit. Targeted genetic lesions of single or multiple steps in the biosynthetic pathway will be generated. Root exudates of resultant plants will be analysed for presence of hatching factors and hatch stimulation and infection of their roots from cyst-infested soil will be assessed.
The persistence of unhatched PCN could also be manipulated through choice of host potato cultivar. Stored lipid is required by the J2 nematode to remain dormant in soil, hatch, invade the root and establish its feeding site. Host potato cultivar can sufficiently influence the initial lipid level provided to each PCN J2 larva to make a difference of 2-3 years in the maximum persistence before infectivity is compromised. The student will determine to what extent variation in initial lipid occurs among nematodes produced on the top 10 UK potato cultivars and if this ranking varies with the nematode populations. Cultivars may rank consistently enabling long-term persistence to be limited by cultivar choice or it could vary between populations and so contribute to high persistence in some fields.
For more information about the Plant Nematology Group, please visit http://www.plants.leeds.ac.uk/people/groups_urw.php and http://www.fbs.leeds.ac.uk/nem/
Related undergraduate subjects:
- Environmental biology
- Molecular ecology
- Plant science