PVY is a serious, yield limiting viral disease of potato found worldwide. PVY can cause yield reductions up of 50% to 80% in heavily infected commercial production lots. It can also cause losses due to tuber necrosis and reduced tuber quality in storage.
PVY primarily infects plant species in the family Solanaceae. PVY is considered to have a wide host range and can experimentally infect plants in many different plant families, but its main economic importance is as a disease of Solanaceous crops, e.g. potato (Solanum tuberosum), tomato, tobacco, tomatillo, pepper, eggplant, petunia as well as solanaceous weeds, such as the nightshades.
PVY is spread by infected tubers. Infected plants will generate infected tubers. Depending on the cultivar and the virus strain, up to 100% of the tubers on a plant can be infected. Plants developing from infected tubers are almost always infected. Infected seed is the most important source of virus inoculum in the field. Volunteer plants developing from tubers left in the field after harvest can also be a significant source of virus as can sprouting plants in cull piles.
PVY is spread by many species of aphids including those that do not feed long term or colonize potato. The infected plants that develop from infected seed serve as sources of virus transmitted by aphids within and between fields during the growing season. As described in the aphid vector section, acquisition and transmission of the virus occurs very quickly, within seconds. It’s unlikely you will see aphid vectors on your potato plants because most of them only alight to taste test the potato plant and then move on. But, during that brief visit, PVY can be acquired and transmitted. While insecticide treatments will prevent aphids from colonizing potatoes, they have little effect at preventing transmission simply because they do not act fast enough to prevent an aphid from taste-testing a plant. More information can be found here PVY Aphid Vectors. Additional photos can be found here PVY Vector Photo Gallery.
PVY is also spread via sap from infected plants. Known as mechanical transmission, this can happen during handling of infected plants and tubers, such as during seed cutting. Tractors and other equipment that cause damage to stems and leaves can also pick up sap containing virus and carry it down the row to infect other plants. Mechanical transmission is a frequently utilized by researchers to infect plants in the laboratory, but it is not considered to be an efficient methods to spread virus in the field.
PVY is an evolving cluster of genetically related virus strains. In the US, there are currently four major strains affecting potato – PVYO, PVYNTN, PVYNWi and PVYN:O. Another strain, PVYN is rarely found. PVYNTN, PVYNWi and PVYN:O are becoming more prevalent.
Older strains:
- PVYO – The ordinary strain, causes severe leaf mosaic, rugosity (wrinkling), leaf drop, leaf yellowing and dwarfing. Few isolates cause tuber necrosis. Lab tests are definitive and symptoms are easy to see making it easy to manage through seed certification.
- PVYN – The necrotic strain, causes mild foliar symptoms in potato. The strain was originally named because it causes severe leaf necrosis in tobacco. This strain is rarely found in the US, but it is partially responsible for the strains listed below.
Emerging strains:
- PVYN:O – This strain is a genetic hybrid of PVYO and PVYN, but it behaves biologically like PVYN, e.g. it causes mild foliar symptoms in potato and leaf necrosis in tobacco.
- PVYN-Wi – The Wilga strain is very similar to PVYN:O in its genetic and biological properties. It can be differentiated from PVYN:O by some sophisticated diagnostic tests and a minority number of isolates of this strain can cause potato tuber necrotic ringspot disease (PTNRD) in some potato cultivars.
- PVYNTN – The tuber necrotic strain is another genetic hybrid of PVYO and PVYN, but differs genetically from PVYN:O and PVYNWi. In general, it causes milder foliar symptoms than PVYO and most isolates of PVYNTN cause PTNRD in susceptible cultivars.