Gymnosporangium

Gymnosporangium is a genus of heteroecious plant-pathogenic fungi which alternately infect members of the family Cupressaceae, primarily species in the genus Juniperus (junipers), and members of the family Rosaceae in the subfamily Amygdaloideae (apples, pears, quinces, shadbush, hawthorns, rowans and their relatives). The common name cedar-apple rusts has been used for these fungi.[1] According to the Dictionary of the Fungi (10th edition, 2008), there are about 57 species in the genus.[2]

Gymnosporangium
Gymnosporangium juniperi
Scientific classification
Kingdom: Fungi
Division: Basidiomycota
Class: Pucciniomycetes
Order: Pucciniales
Family: Pucciniaceae
Genus: Gymnosporangium
R.Hedw. ex DC. (1805)
Type species
Gymnosporangium fuscum
DC. (1805)

In junipers (the primary hosts, see photo), some species form a ball-like gall about 2–4 cm in diameter which produces a set of orange tentacle-like spore tubes called telial horns. These horns expand and have a jelly like consistency when wet. In other species, such as in G. clarvariforme, the telia are produced directly from the bark of the juniper with no obvious gall formation or swelling.[3] The basidiospores are released and travel on the wind until they infect an apple, pear, hawthorn or suitable tree.

On the secondary hosts, the fungus produces yellowish depressions on the leaves. It also infects the fruit, which grows whitish tubes like a Medusa head. These are the spore tubes. These aeciospores must then infect a juniper to complete the life cycle. All the types of spores can spread over long distances.[4]

The fungus does not cause serious damage to junipers, but apple and pear trees can suffer serious loss of fruit production due to the effects of the fungus. Although the genus has a worldwide distribution, its impact depends on availability of its two host plant species. Individual species are found in Northern and Central America, Asia, Europe and the Middle East.[4]

Due to the economic impacts of the rusts in some areas where orchards are of commercial importance, some regions have attempted to ban the planting of and/or eradicate the coniferous hosts.[5]

Selected species
Species Primary host Secondary host Common name
Gymnosporangium amelanchieris Juniperus sect. Juniperus Amelanchier
Gymnosporangium clavariiforme Juniperus sect. Juniperus Amelanchier, Crataegus, Pyrus Crown of Thorns[6]
Gymnosporangium clavipes Juniperus Crataegus, Cydonia Cedar-quince rust, quince rust[7]
Gymnosporangium confusum Juniperus Crataegus, Cydonia, Mespilus, Pyrus
Gymnosporangium cornutum Juniperus sect. Juniperus Sorbus subgen. Sorbus Mountain ash juniper rust[7]
Gymnosporangium cupressi Cupressus Amelanchier
Gymnosporangium dobroznakovii Juniperus sect. Juniperus Pyrus
Gymnosporangium fuscum (syn. G. sabinae) Juniperus sect. Sabina Pyrus Pear rust, European pear rust, or pear trellis rust[7][8]
Gymnosporangium fusisporum Juniperus sect. Sabina Cotoneaster
Gymnosporangium gaeumannii Juniperus communis (not known)
Gymnosporangium globosum Juniperus Crataegus Cedar-hawthorn rust, American hawthorn rust[7][8]
Gymnosporangium gracile Juniperus Amelanchier, Crataegus, Cydonia
Gymnosporangium harknessianum Juniperus Amelanchier
Gymnosporangium inconspicuum Juniperus Amelanchier
Gymnosporangium juniperi-virginianae Juniperus Malus Cedar-apple rust[7]
Gymnosporangium kernianum Juniperus Amelanchier Kern's pear rust[8]
Gymnosporangium libocedri Calocedrus Amelanchier Pacific Coast pear rust,[8] Incense cedar broom rust[7]
Gymnosporangium malyi (not known) Crataegus
Gymnosporangium multiporum Juniperus (not known)
Gymnosporangium nelsonii Juniperus Amelanchier Witches broom rust,[7] Rocky Mountain pear[8]
Gymnosporangium nidus-avis Juniperus sect. Sabina Crataegus, Cydonia, Malus Juniper witches' broom rust[7]
Gymnosporangium sabinae Juniperus Pyrus, Malus, Crataegus Pear rust, European pear rust, or pear trellis rust[7]
Gymnosporangium torminalis-juniperinum Juniperus sect. Juniperus Sorbus torminalis
Gymnosporangium tremelloides Juniperus sect. Juniperus Cydonia, Malus, Sorbus
Gymnosporangium yamadae Juniperus Malus Japanese apple rust[9]

References
  1. Kern, Frank D (1973). Revised Taxonomic Account of Gymnosporangium. Pennsylvania State University Press. p. 136. ISBN 978-0271011059.
  2. Kirk PM, Cannon PF, Minter DW, Stalpers JA (2008). Dictionary of the Fungi (10th ed.). Wallingford, UK: CABI. p. 298. ISBN 978-0-85199-826-8.
  3. Brand, Bert; Brand, Gill; Shattock, Richard (October 2006). "Sorting out Gymnosporangium species – the aecial stage". Field Mycology. 7 (4): 123–127. doi:10.1016/S1468-1641(10)60574-9.
  4. "Diagnostics - Gymnosporangium spp. (non-European)". OEPP/EPPO Bulletin. 36: 41–446. 2006.
  5. "Cedar Apple Rust - Plant of the Week". Archived from the original on 2006-09-26. Retrieved 2006-11-17.
  6. Gymnosporangium cornutum/clavariforme, Scottish Fungi
  7. FullFungi List, Widely Prevalent Fungi of the United States
  8. Diseases of Pear, APS
  9. Gymnosporangium yamadae Archived 2015-06-04 at the Wayback Machine, Data sheets on Quaranteen Pests
  • Phillips, D.H., & Burdekin, D.A. (1992). Diseases of Forest and Ornamental Trees. Macmillan.
  • Scharpf, R.F., ed. (1993). Diseases of Pacific Coast Conifers. USDA Forest Service Agricultural Handbook 521.
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