Addition of Thekopsora minima to the EPPO Alert List
Why: Thekopsora minima is an heteroecious rust which lives on needles of Tsuga spp. (aecial stage) and leaves of ericaceous plants (telial stage). On blueberries (Vaccinium spp.), it can cause a serious rust disease leading to extensive defoliation. The presence of T. minima was detected for the first time in Germany in 2015 and an express-PRA has concluded that this pathogen might present a high risk for Germany and other parts of the EPPO region. The NPPO of Germany has therefore suggested that T. minima should be added to the EPPO Alert List.
Where: initially recorded in the eastern part of North America and Japan, T. minima. has been introduced on Vaccinium corymbosum in other parts of the world (e.g. South Africa, Mexico, Australia, Colombia and Germany) during the last decades. Considering some taxonomic confusion in the past and morphological similarities with other rust fungus attacking Vaccinium spp., the world geographical distribution of T. minima is rather uncertain. In the German PRA, it is argued that some records attributed to Pucciniastrum vaccinii in Argentina, Hawaii (US), and Spain may need to be reconsidered as they might be misidentifications of T. minima.
EPPO region: Germany (first found in 2015; transient).
North America: Canada (no details), Mexico, USA (Delaware, Michigan, New York).
South America: Colombia.
Asia: Japan (no details).
Oceania: Australia (New South Wales, Queensland, Victoria). T. minima was detected in 2014 in Tasmania but subsequently eradicated (destruction of all infected plants)
On which plants: the main host plants are Vaccinium spp. (V. angustifolium, V. corymbosum, V. erythrocarpum). The susceptibility of Vaccinium species that are growing in the wild in the EPPO region (e.g., V. myrtillus, V. vitis-idaea) is not known. The host range also includes Ericaceae species from the following genera: Azalea, Gaylussacia, Hugeria, Leucothoe, Lyonia, Menziesia, Pernettya, Pieris, and Rhododendron. The alternate host is hemlock (Tsuga canadensis, T. diversifolia).
Damage: symptoms appear on the upper surface of blueberry leaves as small, yellow spots that later become necrotic as they enlarge and coalesce, eventually covering large areas of individual leaves. On the undersides of leaves, small flecks surrounded by water-soaked halos appear, turning into yellow-orange pustules. Later in the season, similar pustules can develop on fruits. In case of severe infection, premature leaf drop and plant defoliation is observed. Loss of leaves reduces plant vigour which may lead to a decline in fruit yield and flower production during the following season. The presence of pustules on fruit also leads to crop losses.
The life cycle of the rust has been described as follows. Teliospores of T. minima hibernate on blueberry leaves on the ground and after germination in late spring they infest their alternating host, Tsuga spp., via basidiospores. The produced aeciospores infest Vaccinium and other Ericaceae host plants. The urediniospores which are then produced ensure disease spread within the crop during the whole growing season. However, in closely related rusts attacking blueberries in Europe, it has been shown that these rusts could hibernate as mycelium in the plant buds and directly produce urediniospores in spring, which means that the alternate host is no longer needed. It is not known whether this could happen for T. minima in the EPPO region but in such a case, this would add to the risk.
Dissemination: blueberry rust spores are spread to nearby plants by wind and rain. Over longer distances, trade of infected plants can ensure disease spread. It is also suspected that humans can transport fungal spores on equipment, packaging and clothing.
Pathway: Plants for planting, fruits? of host plants from countries where T. minima occurs.
Possible risks: cultivation of Vaccinium corymbosum in the EPPO region has started in the 1930s, and takes place in several countries (e.g. Poland, Germany, the Netherlands, Sweden, Baltic countries, Russia, Romania, France). Other Ericaceae hosts, in particular azaleas and rhododendrons, are also widely grown in the EPPO region, mainly for ornamental purposes. Tsuga canadensis (alternate host) can also be found in the EPPO region, however the necessity of the alternate host to complete the life cycle remains to be studied under European conditions. Although further studies are needed, the climatic conditions prevailing in the EPPO region appear to be favourable to the establishment of T. minima. In countries where T. minima has been introduced (e.g. Australia and Mexico), the disease is considered to be economically damaging. In Mexico, it is stated that T. minima has become one of the most significant diseases of blueberry in Jalisco and Michoacan states. In Australia, following the successful eradication of T. mimina in Tasmania, phytosanitary measures are in place to protect the island from another introduction. Recently published reports from the USA suggest that damage from blueberry leaf rust has been increasing in the last few years. Although some control methods are available (fungicide treatments, use of tolerant varieties, appropriate irrigation, removal of volunteer hosts), these constitute additional constraints to the growers. Considering the high risk that T. minima could present for cultivated Vaccinium in the EPPO region, and the potential damage that it might cause to wild Vaccinium (e.g. V. myrtillus), it seems desirable to prevent any further spread within the EPPO region.
EPPO RS 2016/058
Panel review date - Entry date 2016-03
Sources
Dawson J, Percival D, Gray B, Pitts N, Hildebrand P (2008) The effect of three foliar diseases of the wild blueberry (Vaccinium angustifolium Ait.) on leaf photochemistry, leaf drop, and floral bud number. Proceedings of the Conference on Plants and Soils: Montreal '08. Ecological Intensification, Biofuels and Bioproducts (Montreal, CA, 2008-07-13/16), p 36.
INTERNET
- Agriculture Victoria (2014-09-10) Detection of blueberry rust in Victoria. http://agriculture.vic.gov.au/agriculture/horticulture/moving-plants-and-plant-products/industry-notices/detection-of-blueberry-rust-in-victoria
- New South Wales Government. Department of Primary Industries (dated January 2016). Blueberry rust. http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0006/590370/PUB15-522-primefact-blueberry-rust.pdf
- Tasmanian Government. Biosecurity Tasmania Fact Sheet (dated October 2014). Blueberry Rust (Thekopsora minima P.Syd & Syd). http://dpipwe.tas.gov.au/Documents/BT_BlueberryRust_factsheet092014.pdf
McTaggart AR, Geering ADW, Shivars RG (2013) Thekopsora minima causes blueberry rust in south-eastern Queensland and northern New South Wales. Australasian Plant Disease Notes 8, 81-83.
Mostert L, Bester W, Jensen T, Coertze S, van Hoorn A, Le Roux J, Retief E, Wood A, Aime MC (2010) First report of leaf rust of blueberry caused by Thekopsora minima on Vaccinium corymbosum in the Western Cape, South Africa. Plant Disease 94(4), 478–478.
Rebollar-Alviter A, Minnis AM, Dixon LJ, Castlebury LA, Ramírez-Mendoza MR, Silva-Rojas HV, Baldovinos-Ponce G (2011) First report of leaf rust of blueberry caused by Thekopsora minima in Mexico. Plant Disease 95(6), p 772.
Salazar Yepes M, Pablo Buriticá Céspedes P (2012) New rusts (Pucciniales) Records on crops and ornamental plants in Colombia. Revista Facultad Nacional de Agronomía, Medellín 65(2), 6691-6696.
Sato, S, Katsuya K, Hiratsuka Y (1993) Morphology, taxonomy and nomenclature of Tsuga-Ericaceae rusts. Transactions of the Mycological Society of Japan 34(1), 47-62 (abst.).
Schilder AMC, Miles TD (2011) First report of blueberry leaf rust caused by Thekopsora minima on Vaccinium corymbosum in Michigan. Plant Disease 95(6), p 768.