Epidemiology & Population Dynamics

An important factor in the understanding of a disease’s development and its potential threat to plant health is the inherent diversity of the pathogen concerned. Such knowledge may allow the origin of an outbreak to be established, or better diagnostic tools to be developed. Study of changes in the pathogen population over time may highlight the potential for new, more aggressive strains to become established or that control measures such as plant resistance are likely to breakdown.

Biofumigation

Control of soil-borne potato diseases using Brassica spp. Mediated Biofumigation

With increasing amounts of pressure put on to growers to cut their use of potential environmental hazardous pesticides and fumigants, a considerable amount of interest is being shown within alternative methods of pathogen and pest control.  One such method has been termed Biofumigation.  It is a method that exploits toxic compounds that are already naturally released via glucosinolate hydrolysis which occurs during the breakdown of Brassica plant tissues. 

Although it is known that the compounds are released during mastication of the Brassica cells, many gaps still exist in our understanding of these, and whether such effects are transferable to a field scale.  This study will uncover a greater in-depth knowledge of biofumigation, which will aid understanding of the complex processes involved and it’s potential to be used as part of an integrated disease management programme. 

TOP: Potato tuber with external symptoms of black scurf.  BOTTOM: Black dot microsclerotia on potato tubers This project will concentrate upon using biofumigation to suppress soil-borne pathogens that infect potatoes, of which there are a significant number of, such as – black dot (Colletotrichum coccodes), silver scurf (Helminthosporium solani), common scab (Steptomyces scabies), stem canker and black scurf (Rhizoctonia solani) and skin spot (Polyscytalum pustulans).  Such diseases are known to cause reduced development of the plant, lower tuber quality and produce unsightly blemishes, which all in turn lead to reduced marketable yield. 

The project will investigate many aspects of the pathogen: biofumigation interaction, initially determining, through the use of in vitro assays, if a proposed system will work within it’s most controllable form.  This data will provide a basic understanding of the processes involved and interpretation of effects observed under a controlled soil environment.  Ultimately to provide scientific robust evidence on the potential role of biofumigation in an integrated control programme.

Phytophthoras

Phytophthora ramorum and Phytophthora kernoviae are two pathogens which in Scotland so far affect mainly hardy ornamental plants like Rhododendron, Viburnum or Magnolia in nurseries and gardens.

Both pathogens have also the potential to cause serious damage to our natural wood- and heathland and are therefore subject of official control and eradication measures. SASA is collaborator in a multidisciplinary research project funded by the Scottish Government combining field studies of selected outbreak sites, modelling of expected disease progress and molecular characterisation of pathogen strains. The aim is to increase our knowledge about disease establishment, spread, risks and impact under Scottish climate and conditions to support official disease management.

Left to right: Simultaneous infection of Rhododendron with Phytophthora ramorum and Phytophthora kernoviae; Oospore of Phytophthora kernoviae; Soil sampling at Phytophthora kernoviae outbreak site.

 

Virus Biodiversity and Epidemiology

Molecular diversity and Epidemiology of Potato virus Y (PVY)

PhD studentship (SASA-University of Nottingham-Potato Council Ltd) 
           
The Scottish seed potato industry accounts for 75% of all UK production and is worth an estimated £80 million. Potato virus Y is widely distributed in the potato growing areas worldwide. PVY is transmitted non-persistently by non-colonizing aphid vectors, resulting in rapid acquisition and transmission of the virus. There are three commonly described PVY strains: ordinary or common strain (PVYO), stipple streak strain (PVYC) and the veinal necrosis strain (PVYN). Surveys of PVY populations worldwide have identified a drift in the PVY population towards recombinant PVYN strains, where so-called PVYNTN(N-Tuber Necrosis) recombinant strains are causing tuber ringspot necrosis. The emergence and spread of PVYNTN strains has led to large economic losses and highlighted the need for accurate discrimination between PVY variants and better understanding of their pathogenicity and epidemiology.

The purpose of our Potato Council funded PhD project is to understand the mechanisms that drive PVY molecular diversity and epidemiology. See also the poster, Biodiversity and Epidemiology of Potato Virus Y. The key aims are:

  • Characterisation of the population structure of PVY field isolates
  • Biological and molecular characterization of major PVY isolates: mapping  genetic determinants responsible of vein necrosis and tuber ringspot necrosis
  • To gain a better understanding of PVY epidemiology
  • To further improve molecular diagnostic methods of viruses
  • Advice on the potential risk effect of PVY (and other viruses) on seed potato production

           
Left to right: Aphid vector of PVY, vein necrosis and tuber ringspot necrosis on potato caused by variants of PVY strain NTN. Electron micrograph of PVY virions (VIDE Plant Virus database, University of Idaho, USA)

Left to right: Aphid vector of PVY, vein necrosis and tuber ringspot necrosis on potato caused by variants of PVY strain NTN. Electron micrograph of PVY virions (VIDE Plant Virus database, University of Idaho, USA).

Aphids and virus transmission in seed potato crop

Potato Council Ltd, Project R428, Consortium SCRI-SASA-SA-SAC-FERA

The aim of this project is to improve control strategies by understanding interactions between virus source, virus trains, aphid species and aphicide effects.

Virus Characterisation

SASA uses molecular biology techniques in its research on viruses – this research includes topics such as identification, detection and variability of viral species. Such research is usually conducted in collaboration with other scientists with specialisms such as virology and antibody production. We participate in molecular characterisation studies of Scottish potato viruses isolated during crop surveillance (e.g. Browning et al., 2004). Mortensen et al. (2010) characterised potato viruses (PVA, PVS, PVV and PVX) found in potatoes originating from Shetland and compared them to viruses from Scottish mainland crops. These studies inform the assay design process which is vital in the production of robust molecular methods such as PCR. 

We collaborate on the molecular characterisation of potato Carlaviruses of quarantine interest, such as Potato Latent Virus (Brattey et al., 2002), Potato Rough Dwarf Virus and Potato Virus P (Nisbet et al., 2006). Related to this is work on identification of viroid isolates from various plants (James et al., 2007). Viroids are unusual plant pathogens, consisting of a naked circle of RNA; they are a great concern in the commercial production of many plant species.

See details of SASA publications on Virus Characterisation mentioned on this page.

 

Relationship between Carlavirus coat proteins (from Nisbet et al., 2006)

Relationship between Carlavirus coat proteins (from Nisbet et al., 2006)