Potato spindle tuber viroid (PSTVd)
Potato spindle tuber viroid (PSTVd) is an infectious agent that causes spindle tuber disease in potatoes and bunchy top disease in tomatoes. Infection can result in loss of yield and reduction in crop quality. In Canada, potatoes with symptoms of PSTVd were first observed in 1918 and infection was prevalent in the 1950's and 60's. The last report of PSTVd in Canadian potato fields was in 1979 and it was declared eradicated from Canada in 2005. PSTVd is on the CFIA list of plant pests regulated by Canada.
PSTVd can infect a wide variety of plants in different plant families. Severe symptoms and loss of yield can result from infection in potato (Solanum tuberosum) and tomato (Solanum lycopersicum). Other plants that may be infected with PSTVd include but are not limited to pepper (Capsicum annuum), eggplant (Solanum melongena), pepino (Solanum muricatum), and sweet potato (Ipomoea batatas), as well as many ornamental plants in the Solanaceae family and several species of wild plants. These plants are often asymptomatic when infected with PSTVd, however they are important pathogen reservoirs from which disease can be mechanically transmitted to potatoes and tomatoes.
PSTVd has a worldwide distribution and is present through much of Europe and Australia. There are isolated reports in Asia, Africa, and South America.
Symptoms and detection
In potato, severe infections can result in low yield with small tubers that are characterized by having an elongated, spindly shape and many prominent eyes. These tubers can have an abnormal skin appearance and often crack with growth. The foliage of infected potato plants may be upright and stunted with small, rough leaflets. In tomato, infection is characterized by stunted growth and leaves that may be mottled, rough, yellowed, and downturned. Infected tomatoes may have reduced yield and fruit may abort or remain hard and unripened. Because of the variability of symptoms and the possibility of asymptomatic infections, molecular techniques are required to confirm infection with PSTVd.
Spread and control
PSTVd can be transmitted through contact or sap transfer between infected and uninfected plants, through the use of contaminated tools and equipment, and through seed and pollen. PSTVd may be transmitted by the green peach aphid (Myzus persicae) if the source plant is also infected with Potato leafroll virus. Without treatment, PSTVd can remain infectious for a prolonged period of time on a wide variety of materials including glass, concrete, and metal. Additionally, PSTVd can readily be transferred to new host plants from asymptomatically infected plants.
There are no products to prevent PSTVd infection and control is achieved through strict implementation of biosecurity measures, including the destruction of infected plant material and sanitation of tools and facilities.
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