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32 POTATO GROWER | NOVEMBER 2019 Living defenses could protect potatoes from virus, nematode threats Defensive Gurus Diggin' In Diggin' In PLANT PROTECTION | By Seth Truscott, Washington State University Helping safeguard the Northwest's valuable potato crop from emerging threats—tiny, parasitic worms and a fungus-like pathogen that spreads a devastating virus—two scientists at Washington State University have launched new research into better plant defenses based on genes and vaccines. Washington State grows the most potatoes per acre of any state in the U.S., producing nearly $700 million worth of spuds per year. But the Northwest's fourth-most valuable crop is threatened by powdery scab, a disease caused by a fungus-like pathogen that also carries a harmful virus. Potatoes are also under attack from the Columbia root-knot nematode, a microscopic worm found in Washington soils. Funded by the USDA's Agriculture and Food Research Initiative (AFRI) and the Northwest Potato Research Consortium, plant pathologists Kiwamu Tanaka and Cynthia Gleason are exploring new molecular and living defenses against these pests. A HIDDEN THREAT Neither fungi nor bacteria, the powdery scab pathogen is a protist, from the same kingdom of life as slime molds and protozoa. Infecting roots and tubers of its potato host, powdery scab forms root galls that stop plants from drawing in nutrients and water. It also damages the tubers' skin, turning potatoes ugly and unsellable. "Farmers struggle to control it, because fungicides don't work very well," says Tanaka, assistant professor and phenomics researcher with the WSU Department of Plant Pathology. Worse, scab also carries a virus, potato mop-top virus, or PMTV. A quarantine pathogen in some countries, the virus disrupts plant growth and causes tuber necrosis: edible potatoes die from the inside. Devastating yields, mop-top virus was first found in the U.S. in 2002, and is now starting to show up in the Northwest. "The scary part is that until you dig up and cut into the potatoes, you don't know it's there," says Tanaka. "It can infect WSU plant pathologists Kiwamu Tanaka and Cynthia Gleason are exploring novel defenses against pest and diseases that harm valuable potato crops.