Potato Review

www.potatoreview.com POTATO REVIEW SEPTEMBER/OCTOBER 2020 23 BLACKLEG CONTROL crop and the water encourages the blackleg to grow. “But we planted mini-tubers that were completely free of the bacteria, over-irrigated them, and in some cases saw 7% blackleg, which for a rst-generation potato crop is unheard of. “ at’s really important as it shows that a contamined seed tuber is not necessarily the only thing that leads to blackleg. What we think is happening is the bacteria are able in certain situations to go in via the root.” For ware growers this is a potentially important discovery, as it means a ne balance might be needed with irrigation to help reduce the incidence of common scab and increasing yields, but not over irrigating and encouraging blackleg, he said. “NIAB’s Mark Stalham is looking at this as part of the project.” Another recent nding from research funded by Scottish Society for Crop Research (SSCR) is that potato plants inoculated with both Pectobacterium atrosepticum and free- living nematodes can have up to 100 times more bacteria in the potato plant than where the free-living nematode wasn’t present. “ at’s very good preliminary evidence that in the eld free-living nematodes probably via their feeding are helping the bacteria get into the plant. “So we are working with NIAB and Bayer to see whether irrigation increases free-living nematodes around the root system of the ➜ How about genetic or biological control? Unlike late blight or potato cyst nematodes where there is a single gene that determines whether a potato variety is resistant to attack from the disease or pest, there doesn’t appear to be a similar gene for blackleg, Ian says. “We’re almost certain that any disease resistance or tolerance you see in the eld to blackleg is from a collection of genes working together, rather than a single gene. Unfortunately breeding that into a variety is di cult so my feeling is we won’t see truly resistant varieties, although the big seed houses are looking.” ere’s more promise with biological controls called bacteriophages. “Bacteriophages are viruses that infect bacteria, and you can nd speci c ones that only infect Pectobacterium atrosepticum so they are safe.” APS Biocontrol already uses them in pre-pack potatoes to increase shelf life, but they are now being tested in foliar applications to see if contamination and therefore disease can be reduced, he says. “A contamined seed tuber is not necessarily the only thing that leads to blackleg.” A weak link in the chain is moving seed potatoes from store to the field where they are planted, Ian suggests. The nematicide Velum Prime (fluopyram) is being used to keep nematodes at bay and potentially control blackleg.