This is a CASE project in collaboration with Barworth Agriculture, a small agricultural and horticultural R & D company based in Lincolnshire.
Potato cyst nematodes (PCNs), commonly known as eel worms, are important soil pests that cause major economic losses to potato growers. They are an intractable problem to farmers both in the UK and in many other countries.
Potato cyst nematodes live as parasites and must complete the majority of their life-cycle in potato roots. The infective 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 is possible because unhatched larvae remain dormant until triggered by stimulus from a suitable host, indicating favourable conditions for hatching. As a result, this survival stage exhibits remarkable longevity, with dormant larvae remaining viable for more than 20 years. This ability to persist in the soil contributes significantly to the economic importance of cyst nematodes.
Persistence and hatching traits of the dormant larvae are influenced by a number of environmental factors as well as genetic characteristics of particular nematode 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.
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 without a host. Decline rates depend on factors such as soil temperature and type, but also vary with 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.
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.
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.
See also http://www.nercdtp.leeds.ac.uk/projects/index.php?id=691