''Gymnosporangium'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

heteroecious A heteroecious parasite is one that requires at least two hosts. The ''primary host'' is the host in which the parasite spends its adult life; the other is the ''secondary host''. Both hosts are required for the parasite to complete its life cycle ...

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

which alternately infect members of the family

Cupressaceae Cupressaceae is a conifer family, the cypress family, with worldwide distribution. The family includes 27–30 genera (17 monotypic), which include the junipers and redwoods, with about 130–140 species in total. They are monoecious, subdio ...

, primarily species in the genus ''Juniperus'' (

juniper Junipers are coniferous trees and shrubs in the genus ''Juniperus'' () of the cypress family Cupressaceae. Depending on the taxonomy, between 50 and 67 species of junipers are widely distributed throughout the Northern Hemisphere, from the Arcti ...

s), and members of the family

Rosaceae Rosaceae (), the rose family, is a medium-sized family of flowering plants that includes 4,828 known species in 91 genera. The name is derived from the type genus ''Rosa''. Among the most species-rich genera are ''Alchemilla'' (270), ''Sorbus ...

in the subfamily

Amygdaloideae Amygdaloideae is a subfamily within the flowering plant family Rosaceae. It was formerly considered by some authors to be separate from Rosaceae, and the family names Prunaceae and Amygdalaceae have been used. Reanalysis from 2007 has shown that ...

(

apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...

pear Pears are fruits produced and consumed around the world, growing on a tree and harvested in the Northern Hemisphere in late summer into October. The pear tree and shrub are a species of genus ''Pyrus'' , in the family Rosaceae, bearing the p ...

quince The quince (; ''Cydonia oblonga'') is the sole member of the genus ''Cydonia'' in the Malinae subtribe (which also contains apples and pears, among other fruits) of the Rosaceae family (biology), family. It is a deciduous tree that bears hard ...

s, shadbush, hawthorns,

rowan The rowans ( or ) or mountain-ashes are shrubs or trees in the genus ''Sorbus ''Sorbus'' is a genus of over 100 species of trees and shrubs in the rose family, Rosaceae. Species of ''Sorbus'' (''s.l.'') are commonly known as whitebeam, r ...

s and their relatives). The common name cedar-apple rusts has been used for these fungi. According to the ''Dictionary of the Fungi'' (10th edition, 2008), there are about 57 species in the genus. In junipers (the primary hosts, see photo), some species form a ball-like

gall Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants, fungi, or animals. Plant galls are abnormal outgrowths of plant tissues, similar to be ...

about 2–4 cm in diameter which produces a set of orange tentacle-like

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

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. The

basidiospores A basidiospore is a reproductive spore produced by Basidiomycete fungi, a grouping that includes mushrooms, shelf fungi, rusts, and smuts. Basidiospores typically each contain one haploid nucleus that is the product of meiosis, and they are pro ...

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 In Greek mythology, Medusa (; Ancient Greek: Μέδουσα "guardian, protectress"), also called Gorgo, was one of the three monstrous Gorgons, generally described as winged human females with living venomous snakes in place of hair. Those ...

head. These are the spore tubes. These

aeciospores Aeciospores are one of several different types of spores formed by Rusts. They each have two nuclei and are typically seen in chain-like formations in the aecium An aecium (plural aecia) is a specialised reproductive structure found in some pl ...

must then infect a juniper to complete the life cycle. All the types of spores can spread over long distances. 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. Due to the economic impacts of the rusts in some areas where

orchard An orchard is an intentional plantation of trees or shrubs that is maintained for food production. Orchards comprise fruit- or nut-producing trees which are generally grown for commercial production. Orchards are also sometimes a feature of larg ...

s are of commercial importance, some regions have attempted to ban the planting of and/or eradicate the coniferous hosts.

Selected species

References

* 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.

External links

Forestry Images: ''Gymnosporangium''

Photo of ''Gymnosporangium sabinae''
on ''

Juniperus sabina ''Juniperus sabina'', the savin juniper or savin, is a species of juniper native to the mountains of central and southern Europe and western and central Asia, from Spain to eastern Siberia, typically growing at altitudes of .Farjon, A. (2005). ' ...

'' {{Authority control Basidiomycota genera Pucciniales