T. areolata is an heteroecious rust, producing the aecial stage on spruce cones (Picea spp.) and the uredinial and telial stage on the leaves of wild cherry trees (Prunus spp.).
The insides of cone scales should be examined for the tough rounded red-brown aecia, particularly on cones that are open early or that are open in wet weather (Murray, 1955). Leaves of cherry [ Prunus spp.] trees will show dark-purple angular spots on both surfaces;the hemispherical orange-yellow uredinia occur on the lower leaf surface. Telia have been reported to occur only on Prunus padus and Prunus virginiana (Hylander et al., 1953) and microscopic examination of the epidermis is required to see the densely packed septate teliospores.
Related invasive species
- Thekopsora areolata
Related Farm Practice
- Effects
T. areolata is a heteroecious rust fungus;an obligate parasite with stages of its life cycle on cones of Picea species and leaves of Prunus spp. Reported from Europe and Asia, the fungus is a Regulated Pest for the USA. It is absent from North America, where susceptible species are native or introduced, and Australia and New Zealand, where such species are introduced. Although usually not a major problem in its native range, this rust could be more damaging as an invasive in other temperate areas. Due to the fact that small amounts of infection may be overlooked, accidental introduction could occur through importation of infected cones carrying aeciospores. The one known introduction to North America involved a tree of Prunus sp. in a garden, from which there was no documented spread.
Whitish spermogonia on the outside of infected cone scales generate a sugary liquid with a strong odour (Murray, 1955;Wilson and Henderson, 1966). The large hemispherical or rounded aecia on the inner surface of scales cause the cones to open early and/or remain open in wet weather (Murray, 1955). Quantities of yellow aeciospores are shed. The resulting infection of Prunus leaves causes angular, violet or reddish-brown spots on the upper leaf surface, with yellow uredinial pustules shedding urediniospores on the lower surface. Telia are in the leaf epidermis, eventually causing reddish-brown to dark-brown discolouration in the spots on the upper surface. Necrosis of leaf tissue may result in a “shot hole” effect, when the affected tissue falls out (Smith et al., 1988).
Roll-Hansen (1965) found infection of young spruce trees to cause crooked stems and necrotic stem lesions with a slightly swollen bark area, often accompanied by dieback of the shoot terminus. Hietala et al. (2008) also reported crooked growth that often accompanied dark-brown necrotic lesions in the bark of seedlings and the leader shoots of saplings. Aecia did not appear on the seedling shoots, but could occur on saplings (Hietala et al., 2008).
The major aecial host is Picea abies, but Roll-Hansen (1965) found that shoots of the North American Picea engelmannii, introduced in Norway, were also infected;there was no report of the infection of cones. Most other Picea species reported are Asian (Hiratsuka et al., 1992;Chen, 2002). Although there are reports of the rust on the important cultivated fruit trees Prunus cerasus (cherry) and Prunus domestica (plum) (Kuprevich and Transchel, 1957;Gjaerum, 1974), the wild Prunus padus and introduced Prunus serotina and Prunus virginiana are more frequently the telial hosts in Europe (Smith et al., 1988).