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Blackleg vigilance

Publication Date: 
19 April 2016

Blackleg vigilance

Blackleg is a long-standing industry concern, although incidence has been significantly reduced since the 1960s, thanks largely to changes to industry practices and the efforts of growers. 

However, during the 2010 and 2011 seasons the incidence of potato Blackleg rose to levels not seen for over twenty years.

Blackleg, caused by Pectobacterium and Dickeya bacteria, is one of the most significant bacterial diseases affecting potato production globally.

In the UK, blackleg is caused primarily by the Pectobacterium species, with the vast majority of cases caused by Pectobacterium atrosepticum (Pba). Although some Dickeya infections are reported in England, all of these are attributable to non-UK origin seed. It is generally accepted to be a seed-borne disease, but the causes underlying the initial infection of high-grade seed remain largely unknown.

In 2013, AHDB Potatoes and The Scottish Government began funding research to understand routes of Pectobacterium contamination in high-grade seed. This project is now nearing completion with interesting take-home messages for the potato industry.

Leading this joint research is The James Hutton Institute’s Ian Toth, working alongside Fera’s John Elphinstone, SASA’s Gerry Saddler and SRUC’s Stuart Wale.  Several approaches were taken to understand routes of contamination, including monitoring sequential high-grade stocks of a susceptible variety on Pre-Basic (PB) farms, investigating in-field spread and studying geographic clustering of disease incidence.  

See AHDB R&D project: 114R475 Routes of Pectobacterium Contamination of High Grade Potato Seed

Interim findings on Blackleg

Monitoring in-field spread has shown that P. atrosepticum can be transmitted from heavily infected plants to adjacent healthy plants causing symptom expression within the same season. Disease can also occur from environmental sources, and harvested tubers have both surface (including lenticels) (2/3) and systemic (1/3) contamination. However low disease incidence was observed in daughter crops.

Using data extracted from SASA’s SPUDS database and modelled by James Hutton Institute’s Pete Skelsey, it was possible to identify Blackleg ‘hot spots’ which shift around from year to year. This suggests that localised environmental conditions can boost disease expression but further work is required to fully understand this phenomena.

Intensive studies on isolates of P. atrosepticum collected in the project have shown that some of these populations were around in the 1950s, suggesting that the pathogen has changed little in sixty years.  Using molecular techniques, a number of different populations of P. atrosepticum have been identified and their prevalence during and across a season have been evaluated.  Both machinery and adjacent crops have been implicated in sources and spread of contamination.

To identify contributing factors which could be leading to a rise in Blackleg, particularly in PB crops, AHDB’s Claire Hodge and SASA’s Gerry Saddler and Triona Davey have completed a survey with growers to investigate social changes and industry practices. The results have demonstrated the commercial pressures on seed growers as their numbers decrease, whilst the area and number of varieties that individual businesses are handling is increasing. A wider survey of commercial seed growers in GB is planned for spring 2016 to complete this work, with results available towards the end of 2016.

From a practical perspective, SRUC’s Stuart Wale explained how the research project has shown that no single measure will effectively control Blackleg.  Attention to detail is critical at all stages of production, storage and transport.  Stuart advises “Over the last two decades, growers have made great strides adopting measures that can reduce the incidence of Blackleg, but as the last few years have shown, vigilance is required to sustain control, especially in wet seasons.”

General advice for Blackleg control

  • Hygiene of field and grading machinery is expensive and time-consuming but can reduce and/or remove some sources of infection
  • Plant and harvest during dry weather. Dry down quickly and store under cool conditions
  • Consider growing each early generation in separate fields
  • Isolation of early generation fields may reduce contamination from outside sources
  • Keep irrigation of all seed crops to a minimum
  • Harvest high-grade stocks as early as possible

For more information contact: Claire Hodge, Knowledge Exchange Manager, Claire.Hodge@ahdb.org.uk,  07771 798 552

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