A PROJECT researching incidences of blackleg in the UK looked at the routes of blackleg contamination of high grade potato seed stocks by pectobacterium species and the effects of sulphuric acid treatment on pathogen spread. 

Speaking at a Scottish Society for Crop Research potato committee meeting at the James Hutton Institute, the institute’s Sonia Humphris said incidents of blackleg had increased in the last four years but researchers are unsure why, so looked at the mechanisms of disease spread. 

“The main cause is pectobacterium spp in the UK, but in Scotland some 93.8% of blackleg findings were caused by pectobacterium atrosepticum (Pba),” explained Ms Humphris. “We then looked at the mechanism of pathogen spread and discovered bacteria on the roots or canopy can enter the plant, with some cultivars more susceptible to this than others.

“Using experimental plots, we tracked the movement of Pba from infected to healthy plants by monitoring the canopy and below ground during the growing season, with samples obtained from leaves, stem and roots at three, six, nine and 12 weeks post-emergence.”

The contamination of plant parts, says Ms Humphris, was hard to detect early in the season and cases of Pba increased with irrigation. 

“We were surprised to discover progeny tuber contamination and blackleg was caused by environmental pectobacterium spp as well as the marker strain, and while contamination was found on plants both above and below ground, the majority was found on the roots and base stem of the plants. There is also evidence of strains moving between fields.”

Using Science and Advice for Scottish Agriculture’s SPUDS database during a four-year period, there was strong evidence of clustering of blackleg-affected seed potato crops. These hot spots of incidences varied year on year – moving from the Black Isle, to Aberdeen, Angus and Tayside – which suggested the disease is unlikely to be linked to production practises at specific geographical locations. 

Ms Humphris also announced two new projects with the first, a three-year project funded by ScotGov, looking at how the seed potato classification scheme can be modified to achieve greater control of blackleg, and may even raise questions on the effectiveness of roguing on reducing disease resistance.

The second, a five-year project funded by AHDB and ScotGov, will look at ways to improve seed management to minimise losses due to pectobacterium spp. This project will aim to identify the major routes of initial contamination of high grade tubers. It will also monitor the seed production process for points within the system that may lead to an increase or decrease in bacterial contamination and will look at developing and testing control options, including phages, UV and ozone.