Vegetatively grown crops such as garlic, potatoes or strawberries are amplified not by seed, but asexually by clones, daughter tubers or cuttings. Unlike true seed production, the offspring of clones have a much higher potential to accumulate viruses and other pathogens in each progressive generation.

Virus infection is generally transmitted by insects like aphids, thrips or leafhoppers. These insects have a stylet that pierces the plant’s cells and if a virus is present, the virus can enter the insects foregut and into the salivary glands. As the insect moves to a new plant and pierces it, some virus-infected saliva may be left behind from the previously visited plant. Virus symptoms don’t always show up at first but can accumulate in clones after years of production while not causing any visible symptoms and cannot be ‘cured’ with a pesticide application. They can still slow the plant down in other ways such as causing a yield drag or making the plant more susceptible to other stressors.

Some crops, like potatoes, have a certified seed program which is federally regulated and has set limits on how much disease and virus can be tolerated. There are also seed classes based on age and disease/virus levels. Other smaller crops, such as garlic, do not have the same regulations; so seed is often reused indefinitely. In garlic, there is the option of growing out bulbils, the seed-like structure that is found in the scape in hardneck varieties. Growing the bulbils can clean the seed of nematodes, bulb mites, fungi and bacteria, but viruses are still found in this part of the plant.

Figure 1. Potato minituber production – OMAFRA.

The SPUD unit at the New Liskeard Agricultural Research Station, University of Guelph provides Ontario growers and researchers a unique resource to obtain truly clean seed for some vegetatively propagated crops. We recently had a chance to visit the SPUD unit which was established in 1983 to service the seed potato industry and is still in operation today.

Figure 2. Virus-freed garlic microplants – OMAFRA.

What is particularly unique about the research facility at New Liskeard is where it is located. This latitude still experiences enough growing degree days for field trials, yet it is typically sheltered from the effects of the jet-stream throughout most of the growing season. This is important, as the jet-stream has been known to carry virus-transmitting aphids. This allows for the amplification of clean stock with a lower risk of virus infection.

Figure 3. Garlic plants in the greenhouse – OMAFRA.

In garlic, the cells of the meristem / shoot tip of a scape can grow faster than the virus can infect the cells. Meristem tips are cut and placed on a media and under lights and ideal conditions they grow without the rest of the plant present. A mass of cells, known as a differentiated callus, develops and root and shoot hormones are used to produce, you guessed it, roots and shoots. This plant tissue is then tested for viruses multiple times and if clean, these plants are then multiplied and used to create bulbs, called roundels, for field production.

Clean ‘Music’ seed can be ordered through the Ontario Garlic Growers Association and shipped directly to your farm from the SPUD unit. If you are looking to clean up your own garlic or potato cultivar through the SPUD unit, contact Candy Keith at or 1 (705) 647-8525 ext 230. The process to ‘clean’ a new garlic cultivar may take between 36-48 months while for potato it will depend on the cultivar and the space available at the SPUD unit based on currently ongoing projects.

Figure 4. Cloves/roundels ready for the field – OMAFRA

The University of Guelph, New Liskeard Agricultural Research Station is a unique and special resource that is available to Canadian growers. Since 1983, the SPUD Unit has helped create clean seed for many horticultural crops. It has been a breeding site for strawberries and a winter hardiness of both strawberries and raspberries. Field production research has included trials for cucumber, tomato, sweet corn, bok choy, cauliflower, cabbage, broccoli, green beans and garlic.

Article written by Dennis Van Dyk and Travis Cranmer, vegetable crops specialists.