Potato Early Dying a silent yield killer

Industry network seeks to reduce impact of the disease

Blocked tissues that transport water cause the telltale wilting and death of Potato Early Dying disease.

A national initiative to reduce the severity of a silent enemy in Canadian potato fields is claiming some early success halfway through its four-year program.

The Canadian Potato Early Dying Network (CanPEDNet) is starting to learn more about verticillium wilt and how to deal with this major yield-limiting pathogen in commercial potato cropping systems, said Mario Tenuta, the network’s principal investigator.

The goal is to help potato growers identify verticillium in their fields, predict potential yield losses and provide tools to control the disease, said Tenuta, a University of Manitoba soil scientist.

It’s hoped the network’s efforts will increase potato production and profitability by helping to protect crops from what may be the most serious yield-limiting potato disease in Canada, Tenuta said.

Potato Early Dying (PED) is a fungal disease which can either cause plants to die or drastically reduce yields by robbing tubers of their full growth.

Tenuta said PED can cause yield losses ranging between five and 20 per cent, although some U.S. research puts yield declines as high as 50 per cent.

Other potato diseases such as late blight can be controlled by spraying fungicides onto potato foliage. But PED is more insidious because the fungus which causes it is in the soil and difficult to treat.

“It’s a really tough fungus to control,” said Tenuta. “It can be challenging to get rid of it completely.”

PED is caused by Verticillium dahliae, a soil-borne fungus that infects the potato plant through the root system. As Tenuta explains it, the fungus colonizes the root and moves through the plant into the stems and leaves. As the plant grows and puts down more leaves, the fungus continues to spread through the tubes or pipes that move water through the plant.

The diseased plant mounts a defence mechanism to cut off the fungus’s movement by blocking the tubes moving the water. This compromises the plant’s ability to move water to the leaves, which then start to wilt and die, preventing sugars and other nutrients from reaching the developing tubers. The result: small tubers and price discounts at processing plants because the potatoes are too short for making french fries.

Worse still, the disease cycle isn’t finished yet. As the plant dies, the fungus starts to produce resting structures called microsclerotia allowing fungi to return to the soil and survive there for years.

Tenuta said PED is a serious problem everywhere in Canada, including the Atlantic provinces, Ontario, Manitoba and Alberta.

The disease is further aggravated by certain nematodes (small parasitic worms) in the soil which feed on potato roots and weaken the plant’s ability to protect itself.

This is where CanPEDNet comes in with projects designed to learn more about the pathogen, relate that knowledge to disease levels and yield losses, and evaluate control practices in commercial potato fields.

Tenuta said the network currently has eight projects in Prince Edward Island, New Brunswick, Quebec, Ontario, Manitoba and Alberta.

He said some work has slowed because the COVID-19 pandemic forced government research laboratories to shut down. Still, the network is making strides on developing protocols for identifying and counting verticillium fungi in soil samples.

Other projects involve tracking disease levels in fields and evaluating control measures such as fungicides, fumigants and crop rotations, Tenuta said.

CanPEDNet is funded jointly by Agriculture and Agri-Food Canada, industry partners and grower groups, including Manitoba’s Keystone Potato Producers Association. More information about the network is available at soilecology.ca.

Begun in 2019, the project is slated to end in 2023. Tenuta said he expects the network will apply for renewal after that.

Tenuta and his colleague Dmytro Yevtushenko of the University of Lethbridge gave a presentation on CanPEDNet during the online Canadian Potato Summit in February.

Tenuta said he appreciates producers’ participation, despite recent difficulties involving wet fields, unharvested crops, early frosts and now the COVID pandemic.

“We acknowledge the challenges that the past couple of years have had. So, I must admit I’m very thankful to our growers to stick with us in these tough times. They’ve really been with us for this project. They know it’s a long-term issue.”

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