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Transcript
Plant Pest Threat - Potato Spindle Tuber Viroid (PSTVd) Look out for Potato Spindle Tuber Viroid (PSTVd) What is it? Potato spindle tuber viroid (PSTVd) is a quarantinable pathogen of Australia and poses a serious threat to Australia's potato and tomato crops. PSTVd was first reported in North America where it has been found in isolated pockets in northern and north eastern USA and Canada and has spread to other continents via the movement of infected potato tubers. The disease is reported to occur in Asia, Africa, North America, South America, Europe, China and recently in New Zealand. In Australia, PSTVd has been reported in tomatoes in Western Australia, Queensland New South Wales and South Australia. What do I look for? Symptoms of PSTVd can be very difficult to diagnose as expression is dependent on the strain of the viroid, plant cultivar infected and climatic conditions. Symptoms can easily be confused with nutrient imbalances, spray damage or other plant diseases. Mild and severe strains of PSTVd do occur and symptoms are usually more pronounced under high light intensity and temperature. Many cultivars of potato and tomato may be symptomless and act as carriers of the disease. Foliar symptoms of potato include an upright and stunted growth habit with an erect stem and shortened internodes between leaflets resulting in an overlapping appearance. The leaflets are often smaller in size with a rugose appearance. Infected potato tubers are often elongated with pointed ends, have deeper eyes than normal and the tuber skin is often cracked. On severely affected tubers, knobs and swellings may appear. In tomatoes there is a long latent period of 4 to 5 weeks (or longer, depending on the PSTVd strain and environmental conditions) before symptoms are expressed. In mature tomato plants infected with severe strains of PSTVd, symptoms include purpling and yellowing of the leaflets, shortening of the leaflet internodes, leaf epinasty (downward bending of leaves or other plant parts, resulting from excessive growth of the upper side), thickening, distortion and leaf brittleness. Spindly shoot growth can occur, flowers may abort and the fruit can be dark green in colour. Plant Pest Threat - Potato Spindle Tuber Viroid (PSTVd) Tomato plant infected with PSTVd showing purpling, chlorosis, down-curling, stunting and distortion. Photo: Department of Agriculture and Food, Western Australia Hosts PSTVd has been detected in avocado (Persea americana), sweet cucumber (Solanum mericatum) and an Australian native Solanum spp. Several important Solanaceous crops, potato (Solanum tuberosum), tomato (Lycopersicum esculentum) and eggplant (Solanum melongena), are also natural hosts of PSTVd. How is PSTVd Spread? PSTVd is a highly contagious disease, transmitted between plants by touch. The use of cutting or pruning tools, contaminated machinery or any form of physical contact between plants can result in disease transmission. PSTVd has been transmitted by the aphid Myzus persicae from plants that are co-infected with potato leafroll virus. In potatoes the most important means of PSTVd spread from one generation to the next is via infected potato tubers. PSTVd is transmitted through pollen and true seed and can retain its infectious activity in seed for long periods. It is transmitted through potato and tomato true seed at varying rates depending on the host cultivar, the presence of PSTVd in one or both of the botanical parents, and the strain of PSTVd present. If you see anything unusual, call the Exotic Plant Pest Hotline 1800 084 881 Plant Pest Threat - Potato Spindle Tuber Viroid (PSTVd) Supported By Queensland Government Department of Agriculture, Fisheries and Forestry New South Wales Government Primary Industries Agriculture ACT Government Territory and Municipal Services Victorian Government Department of Environment and Primary Industries Tasmanian Government Department of Primary Industries, Parks, Water and Environment South Australian Government Primary Industries and Regions Western Australian Government Department of Agriculture and Food Northern Territory Government Department of Primary Industry and Fisheries Commonwealth Government Department of Agriculture Disclaimer The material in this publication was prepared from the most up-to-date information available at the time of publication. It is intended as a guide only and the publisher accepts no responsibility for errors. Biosecurity SA October 2013