Routes of Pectobacterium atrosepticum (Pba) contamination of high-grade seed potatoes

There is no evidence that new strains of Pectobacterium are responsible for the increased levels of blackleg that had been seen in Scotland. Ninety-five per cent of the blackleg recorded in seed crops is attributed to Pectobacterium atrosepticum (Pba)

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.

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.

Sector:

Potatoes

Project code:

114R475

Date:

01 April 2013 - 31 May 2016

Funders:

Scottish Government

AHDB sector cost:

£149,176

Total project value:

£299,176

Project leader:

James Hutton Institute, SASA, SRUC,

To identify how and when early field generations become contaminated/infected by Pectobacterium atrosepticum