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 Maloideae (apples, pears, quinces, shadbush, hawthorns, rowans and their relatives).

In junipers (the primary hosts) (see photo), the fungus forms a ball 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. The spores are released and travel on the wind until they infect an apple, pear, or hawthorn 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. The spores must then infect a juniper to complete the life cycle.

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. 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. Selected species

Species Primary host Secondary host
Gymnosporangium amelanchieris Juniperus sect. Juniperus Amelanchier
Gymnosporangium clavariiforme Juniperus sect. Juniperus Amelanchier, Crataegus, Pyrus
Gymnosporangium clavipes Juniperus Cydonia
Gymnosporangium confusum Juniperus Crataegus, Cydonia, Mespilus, Pyrus
Gymnosporangium cornutum Juniperus sect. Juniperus'' Sorbus subgen. Sorbus
Gymnosporangium cupressi Cupressus Amelanchier
Gymnosporangium dobroznakovii Juniperus sect. Juniperus Pyrus
Gymnosporangium fuscum (syn. G. sabinae) Juniperus sect. Sabina Pyrus
Gymnosporangium fusisporum Juniperus sect. Sabina Cotoneaster
Gymnosporangium gaeumannii Juniperus communis (not known)
Gymnosporangium globosum Juniperus Crataegus
Gymnosporangium gracile Juniperus Amelanchier, Crataegus, Cydonia
Gymnosporangium harknessianum Juniperus Amelanchier
Gymnosporangium inconspicuum Juniperus Amelanchier
Gymnosporangium juniperi-virginianae Juniperus Malus
Gymnosporangium kernianum Juniperus Amelanchier
Gymnosporangium libocedri Calocedrus Amelanchier
Gymnosporangium malyi (not known) Crataegus
Gymnosporangium multiporum Juniperus (not known)
Gymnosporangium nelsonii Juniperus (not known)
Gymnosporangium nidus-avis Juniperus sect. Sabina Crataegus, Cydonia, Malus
Gymnosporangium torminalis-juniperinum Juniperus sect. Juniperus Sorbus torminalis
Gymnosporangium tremelloides Juniperus sect. Juniperus Cydonia, Malus, Sorbus
Gymnosporangium yamadae Juniperus Malus

References and external links

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