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114R475 Routes of Pectobacterium Contamination of High Grade Potato Seed

Publication Date: 
18 April 2017
Author/Contact :
Author/Contact: 
Ian Toth

Contractor :
Contractor: 
James Hutton Institute (JHI)

Full Research Project Title: An investigation into the routes of blackleg contamination of high grade potato seed stocks by Pectobacterium species
Duration: April 2013 - May 2016

Aims

To identify how and when early field generations become contaminated/infected by Pectobacterium atrosepticum (Pba), the environmental conditions that lead to this, and to use this information to modify current control strategies to minimise infection/contamination to ensure subsequent field generations do not become over-run by the pathogen. To compare currently available haulm destruction treatments with sulphuric acid in their effect on spread of Pba.

Approach

AHDB Potatoes and Scottish Government funded a three year project to identify how and when early field generations become infected by P. atrosepticum (Pba). The main components of the project were:

  • Monitoring of two PB1 crops through a 3 year multiplication cycle with active grower participation.
  • Understanding the movement of Pba from infected to healthy plants.
  • Determining the routes by which daughter tubers become infected once Pba is present in or on a plant.
  • Determining whether the population of Pba has changed / is changing over time.
  • Comparing the effectiveness of sulphuric acid in comparison with current standard haulm desiccation programmes to determine their relative impact on Pba spread and infection of progeny tubers.

Some of the key findings from the work are:

  • There is no evidence that new strains of Pectobacterium are responsible for the increased levels of blackleg seen in Scotland over recent years. In Scotland 95% of blackleg recorded in seed crops is attributed to Pectobacterium atrosepticum (Pba)

  • From the testing carried out in three years of monitoring, mini-tubers of the cultivar Desiree were found to be free from any pectolytic bacteria.Routine testing by SASA of a number of mini-tuber stocks each year supports this finding.

  • In field trials, contamination from the environment was observed to result in blackleg in the same season.

  • Results from this and a related study (R454/R491) suggest that local/environmental sources of infection are an important source of blackleg development as well as contaminated seed.

  • Pathogen numbers continue to increase particularly on below-ground parts of a potato plant, towards the end of the growing season, where they are more likely to spread to progeny tubers and/or lead directly to blackleg disease (especially in wet conditions). The longer tubers are left in the ground, therefore, the higher the likelihood of tuber contamination and disease occurring.

  • Tuber testing showed that stolon contamination occurred almost as often as lenticel contamination, which suggests that testing for both could improve diagnostics and help to relate detection to subsequent blackleg disease.

  • In field trials where Pba had been deliberately introduced into the plots to monitor spread of the bacteria, between 20 to 70% of harvested plants had contaminated tubers, depending on the variety or year of sampling. The majority of contaminated tubers were harvested from symptom-free plants. When a sample of the harvested tubers (from both symptomatic and symptom-free plants) were replanted the following year disease levels in the progeny plants were very low, regardless of whether the mother plant was symptomatic or not.

  • Glasshouse experiments were used to study internalisation and movement of Pba from leaves or roots to other parts of the plant. Following inoculation of leaves or roots, the bacteria were often found inside the plant suggesting entry and subsequent colonisation. Marfona showed most entry and movement and Osprey the least, particularly following inoculation of intact leaves, suggesting that internalisation and subsequent blackleg disease may be cultivar dependant.

  • There is some evidence that use of sulphuric acid reduces the contamination of progeny tubers.

  • Blackleg is not a random event but is clustered geographically, with high and low spots that change from year to year. This suggests that blackleg problems are not farm or local area associated across years but when problems do occur they are often accompanied by other blackleg problems in that area. The reason(s) for this is so far unclear, although localised weather conditions are expected to play a role.

 

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