| | Potato leafroll virus | Potato virus Y | Potato mop top virus | Potato spindle tuber viroid
Return to the Guide to Commercial Potato Production on the Canadian Prairies.
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Of the more than 27 viruses that have been reported to infect potatoes, potato leafroll virus (PLRV) and potato virus Y (PVY) are distributed worldwide and have often been reported to be the most damaging. These are the two most economically important viruses in the Prairie potato crop.
Potato Leafroll Virus
Courtesy of R. Singh, Agriculture and Agri-food Canada
PLRV is an aphid-transmitted virus. Primary symptoms appear after the virus is transmitted from an infected aphid to a healthy plant. Primary symptoms include upright, rolled leaves and slight yellowing that appears mainly in the young leaves. In some cultivars, young leaves are pink to reddish beginning at the leaf margins. Leaf rolling may only be evident at the base of the leaflet rather than the whole leaflet, and may eventually spread to the lower leaves. Plants infected early in the season may also be dwarfed. In late season infections, primary symptoms may not appear, as potato plants develop resistance to foliar infection with age, which makes diagnosis difficult.
Secondary symptoms occur when an infected tuber produces an infected plant. Leaf yellowing, along with leaf rolling are often associated with the lower leaves. Leaves are dry, stiff and leathery, and make a paper-like, crisp sound. Plants are often stunted. Secondary symptoms are not as evident in the top of a plant.
PLRV causes net necrosis in infected tubers, rendering them unmarketable. Internal net necrosis is visible when the tuber is cut and is particularly marked in certain cultivars, the most susceptible being Russet Burbank. Net necrosis causes browning of the vascular system within the tuber and is primarily seen when the virus is spread to healthy plants from aphids. It can be seen in tuber-borne infected plants if the disease pressure is high. Timing of net necrosis development in the tuber is dependent on the time of infection in the field. At harvest, tubers may exhibit net necrosis if the plant was infected with the virus early in the growing season. If infection occurred in August or later, net necrosis will not likely show up at harvest but will develop later in storage.
PLRV infection may result in reduced tuber size and number, and yield loss can be as severe as 60-90%. PLRV can also result in rejection of seed lots for certification, and infected tubers with net necrosis are not acceptable for processing.
PLRV is spread primarily by aphids that colonize potatoes, but it is also tuber-borne and therefore spread by infected seed tubers. The most efficient vector is the green peach aphid (3.6.2 Insect Management). PLRV is the only known persistently transmitted potato virus. Persistent means that once the aphid acquires the virus, it carries it for life. PLRV is concentrated in the phloem (vascular) tissue of the plant and is acquired only by an aphid that chooses to feed on an infected plant. Once the aphid acquires the virus from an infected plant, at least 24 hours or more are needed until the newly infected aphid can transmit the virus. Long distance spread of the virus occurs by wind-borne winged aphids. Short distance spread occurs by non-winged aphids moving from plant to plant. PLRV is not mechanically transmitted and therefore aphids are solely responsible for the in-season spread of the disease. Sources of PLRV include plants grown from infected tubers and diseased volunteer potato plants.
Control strategies:
- Plant virus-free, certified seed, remove volunteer hosts, and rogue infected plants early to eliminate virus inoculum.
- Management of aphids is an integral part of PLRV management. Control aphids to eliminate aphid vectors during seed production, during aphid population outbreaks and when cultivars susceptible to net necrosis are grown.
- Scout fields regularly and use established action thresholds to determine when insecticide sprays are recommended
Potato Virus Y
Courtesy of D. Lidgett, Manitoba Seed Grower's Association
PVY is a common virus that may infect many crops including potato, tobacco, pepper and tomato. Common strains of the virus PVYO occur worldwide. Primary symptoms of PVYO, depending on the cultivar, are necrosis, yellowing of leaflets, mottling, leaf dropping and sometimes premature death. Necrosis may cause leaves to collapse and remain attached to the stem.Symptoms of secondary PVYO infection include mottling, crinkling of the leaves, and stunting of the plants. Foliar and stem necrosis may occur. Necrosis following primary infection is usually more severe than following secondary infection. The foliar mosaic symptom (intermingled light green and yellow coloration) may be masked at high (77°F or 25°C) and very low (50°F or 10°C) temperatures, but at high temperatures the disease can be identified by the rugosity (crinkling) of the foliage.
PVY is one of the more damaging potato viruses and can have a significant impact on yield. Infection results in reduced tuber number and size. Complete failure of a potato crop may also occur. PVY can also result in rejection of seed lots for certification.
PVY is an aphid-transmitted virus and spread depends mainly on the presence of winged aphids. PVY is transmitted in a non-persistent manner. The aphid can acquire the virus and infect healthy plants in only a few seconds. After a brief period of feeding on healthy plants, infected aphids rapidly lose their virus charge and must again feed on a PVY infected plant to continue to transmit PVY. To determine suitability of a plant as a host, aphids sap-sample the epidermal tissue of a plant. Many aphid species that don't reproduce on potatoes will sap-sample potato foliage, and during this process can spread PVY.
Control strategies
- Crop borders planted to non-virus host plants such as soybean or wheat provide a landing site where aphids can “clean” their mouthparts from non-persistent viruses before moving into the potato crop. Spread of PVY in potato from sources outside the field can be reduced by up to 60% by using crop borders.
- Plant virus-free, certified seed
- Plant early and rogue out diseased plants
- Apply effective aphidicides
- Vine-kill as early as possible and continue use of an effective aphidicide if needed until vines are completely dead
Potato Mop-Top Virus
PMTV is considered to be an economically important disease of potato. It occurs throughout parts of Europe, South America, Asia, and has recently been detected in North America. PMTV is present in Canada, but the distribution within the country is not known. Foliar symptoms of the disease include dwarfing of shoots resulting in a “mop-top” appearance; pale green V-shaped markings on young leaves; and bright yellow blotches, mottling, rings, and V-shapes on leaves. Tuber symptoms of PMTV infection may include cracking, internal spots, and necrotic rings or arcs referred to as spraing. Tuber symptoms may be difficult to distinguish from tobacco rattle virus or physiological disorders.
PMTV is spread by Spongospora subterranea, the fungus that causes powdery scab. The virus survives in the soil within the spore, and together the spore and virus may remain dormant for many years. Plants become infected with PMTV when virus-carrying powdery scab spores infect potato roots, stolons, or tubers. PMTV is also seedborne. Symptom expression in foliage and tubers is quite variable and is influenced by the type of infection (soil or seed-borne), cultivar, and environmental conditions.
Control strategies
- Avoid introducing powdery scab and PMTV into uninfested soils by using disease free seed and sanitation practices. Sanitation should be aimed at preventing the movement of powdery scab infested soil on seed, equipment, and in irrigation water.
Follow control recommendations for powdery scab.
For further details regarding virus management in seed potatoes, please see selected reference number 4.
Selected References
- Delgado-Sanchez, S. and Grogan, R.G. 1970. Potato Virus Y. No. 37 in: Descriptions of Plant Viruses. Commonw. Mycol. Inst., Assoc. Appl. Biol., Kew, Surrey, England.
- Stevenson, W.R. (Editor). 2001. Compendium of Potato Diseases – Second Edition. APS Press, St. Paul, MN. 125 pp.
- Peters, D. 1970. Potato leafroll virus. No. 36 in: Descriptions of Plant Viruses. Commonw. Mycol. Inst., Assoc. Appl. Biol., Kew, Surrey, England.
- Radcliffe, E.B., Ragsdale, D.W., MacRae, I.V. and Suranyi, R. 1999. Aphid Alert. Recommendations for virus control in seed potatoes. http://ipmworld.umn.edu/aphidalert/alert7.htm
- Waterworth, H.E. and Hadidi, A. Economic losses due to plant viruses. Pages 1-13 In: Plant Virus Disease Control. A. Hadidi, R.K. Khetarpal and H. Koganezawa, eds., APS Press, St. Paul, MN, 684 pp.
Potato Spindle Tuber Viroid
PSTVd is a serious disease of seed potatoes caused by the spindle tuber viroid. The Canadian Food Inspection Agency has a zero tolerance for PSTVd in seed potatoes. Plants infected with PSTVd are upright, dwarfed, and much thinner than uninfected plants. The stems are often more branched and the branches form very sharp angles where they join to the stem. Affected tubers are dwarfed and are usually narrow and spindle-shaped. Eyes are numerous and the tubers are often cracked. PSTVd is spread by contact, but chewing and sucking insects such as aphids, grasshoppers, Colorado potato beetles, and flea beetles have been implicated in the field spread of this disease. Seed-cutting knives, planters and infected seed (tubers and true seed) also spread PSTVd.
Control strategies
- Plant certified disease free seed
- Plant whole seed
- Wash knives and other equipment with detergents, household bleach or quaternary ammonia compounds, especially between seed lots
- Control insects
- Remove diseased plants, ensuring that the entire plant is removed.
- Avoid leaf contact by people and equipment during field operations
Written by Tracy Shinners-Carnelley, Piara Bains, Debbie McLaren, Jill Thomson |
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