PESTS AND DISEASES Potato growers now have more effective strategies for controlling potato virus Y, thanks to the findings of a major Canadian research study. FIGHTING POTATO VIRUS Y P by Mark Halsall otato virus Y (PVY) affects both yield and the quality of the crop, making it one of the most dangerous diseases faced by commercial potato producers. Spread by aphids and through infected seed lots, PVY has been managed with varying levels of success by Canadian growers for many years, but the rise of more aggressive and faster-spreading strains has made it even more challenging to control. For the past five years, a major Canadian research study has been looking into developing more effective strategies for controlling PVY. The project is co-ordinated by the Canadian Horticultural Council and funded by the Canadian Agri-Science Cluster for Horticulture 2, as well as potato industry partners, and wraps up in March 2018. Mathuresh Singh, the director of Agricultural Certification Services in Fredericton, is the project lead. Singh says the research has led to a greater understanding of new strains of PVY and their effect on commercial potato varieties. He adds it has also identified numerous science-based best management practices for reducing the disease spread on farms, which in severe cases can see yield losses due to PVY of up to 80 per cent. There are currently three types of PVY in Canada: PVY O and two newer strains, PVY N:O/Wi and PVY NTN . Singh says the study has confirmed that the newer, more necrotic strains are displacing PVY O in several important potato-growing provinces. Necrotic symptoms can cause tubers to rot, leading to losses in both yield and quality. The study has also catalogued the impacts of each of the PVY strains on close to 30 commercial potato varieties, including Russet Burbank, the main processing potato in Canada. According to Singh, Russet Burbank potatoes are highly susceptible to PVY but typically only show foliar symptoms. “We have not found any tuber symptoms in Russet Burbank in any of our screens, but we did see some loss in yield,” Singh says. “The disease reduces the plant vigour, and that leads to less tuber production.” The researchers have identified a number of commercial varieties, such as Innovator and Viking, that are less susceptible to the new strains in terms of visible symptoms and tuber yield loss. They have also found that two varieties, Eva and Musica, appear to be resistant to infection by any strain of the virus. The research has also shown that PVY N:O/Wi and PVY NTN have a greater transmission efficiency than PVY O . Singh says the rise of PVY NTN is particularly troublesome because of its high transmission rate, as well as its ability to cause necrotic rings on tubers. Most potato cultivars with the PVY NTN strain will exhibit mild to no 16 TOP CROP MANAGER/POTATOES IN CANADA | Spring 2018 Pictured is a comparison of symptoms expressed by three PVY strains on AC Chaleur potato plants that were grown in a greenhouse from disease-free plantlets. Six weeks after artificial inoculation of plants with the PVY O , PVY N:O/wi and PVY NTN strains, the infected plants exhibit variable symptoms compared to the virus-free “control” plant. ABOVE: PHOTO COURTESY OF AGRICULTURAL CERTIFICATION SERVICES.