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. According to the Dictionary of the Fungi (10th edition, 2008), there were 57 species in the genus. In 2023, Species Fungorum lists up to 74 species.
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. 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.
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 orchards are of commercial importance, some regions have attempted to ban the planting of and/or eradicate the coniferous hosts.
In 2020, the monotypic family Gymnosporangiaceae was proposed to accommodate Gymnosporangium. As accepted by Wijayawardene et al. 2020.
Selected species and hosts SpeciesPrimary hostSecondary hostCommon nameGymnosporangium amelanchieris Juniperus sect. Juniperus AmelanchierGymnosporangium clavariiforme Juniperus sect. Juniperus Amelanchier, Crataegus, Pyrus Tongues of FireGymnosporangium cornutum/clavariforme, Scottish FungiGymnosporangium clavipes Juniperus Crataegus, Cydonia Cedar-quince rust, quince rustGymnosporangium confusum Juniperus Crataegus, Cydonia, Mespilus, PyrusGymnosporangium cornutum Juniperus sect. Juniperus Sorbus subgen. Sorbus Mountain ash juniper rustFullFungi List, Widely Prevalent Fungi of the United StatesGymnosporangium cupressi Cupressus AmelanchierGymnosporangium dobroznakovii Juniperus sect. Juniperus PyrusGymnosporangium fusisporum Juniperus sect. Sabina CotoneasterGymnosporangium gaeumannii Juniperus communis (not known)Gymnosporangium globosum Juniperus Crataegus Cedar-hawthorn rust, American hawthorn rustGymnosporangium gracile Juniperus Amelanchier, Crataegus, CydoniaGymnosporangium harknessianum Juniperus AmelanchierGymnosporangium inconspicuum Juniperus AmelanchierGymnosporangium juniperi-virginianae Juniperus Malus Cedar-apple rustGymnosporangium kernianum Juniperus Amelanchier Kern's pear rustDiseases of Pear, APSGymnosporangium libocedri (Now Gymnotelium blasdaleanum, Pucciniaceae family) Calocedrus Amelanchier Pacific Coast pear rust, Incense cedar broom rustGymnosporangium malyi (not known) CrataegusGymnosporangium multiporum Juniperus (not known)Gymnosporangium nelsonii Juniperus Amelanchier Witches broom rust, Rocky Mountain pearGymnosporangium nidus-avis Juniperus sect. Sabina Crataegus, Cydonia, Malus Juniper witches' broom rustGymnosporangium sabinae Juniperus Pyrus, Malus, Crataegus Pear rust, European pear rust, or pear trellis rustGymnosporangium torminalis-juniperinum Juniperus sect. Juniperus Sorbus torminalisGymnosporangium tremelloides Juniperus sect. Juniperus Cydonia, Malus, SorbusGymnosporangium yamadae Juniperus Malus Japanese apple rustGymnosporangium yamadae , Data sheets on Quaranteen Pests
Full list of species As accepted by Species Fungorum;
Gymnosporangium amelanchieris Gymnosporangium annulatum Gymnosporangium asiaticum Gymnosporangium atlanticum Gymnosporangium aurantiacum Gymnosporangium bermudianum Gymnosporangium bethelii Gymnosporangium biseptatum Gymnosporangium clavariiforme Gymnosporangium clavipes Gymnosporangium confusum Gymnosporangium connersii Gymnosporangium corniculans Gymnosporangium corniforme Gymnosporangium cornutum Gymnosporangium cunninghamianum Gymnosporangium cupressi Gymnosporangium davisii Gymnosporangium dobrozrakovae Gymnosporangium echinulatum Gymnosporangium effusum Gymnosporangium exiguum Gymnosporangium exterum Gymnosporangium floriforme Gymnosporangium formosanum Gymnosporangium fraternum Gymnosporangium fusisporum Gymnosporangium gaeumannii Gymnosporangium gjaerumii Gymnosporangium globosum Gymnosporangium gracile Gymnosporangium gracilens Gymnosporangium harknessianum Gymnosporangium hemisphaericum Gymnosporangium huanglongense Gymnosporangium hyalinum Gymnosporangium inconspicuum Gymnosporangium juniperi-virginianae Gymnosporangium kanasense Gymnosporangium kernianum Gymnosporangium lachrymiforme Gymnosporangium lianhuaense Gymnosporangium meridissimum Gymnosporangium mespili Gymnosporangium minus Gymnosporangium miyabei Gymnosporangium monticola Gymnosporangium multiporum Gymnosporangium nelsonii Gymnosporangium nidus-avis Gymnosporangium niitakayamense Gymnosporangium nipponicum Gymnosporangium orientale Gymnosporangium padmarense Gymnosporangium paraphysatum Gymnosporangium pleoporum Gymnosporangium przewalskii Gymnosporangium raphiolepidis Gymnosporangium sabinae Gymnosporangium shennongjiaense Gymnosporangium shiraianum Gymnosporangium sorbi Gymnosporangium spinulosum Gymnosporangium taianum Gymnosporangium tiankengense Gymnosporangium tianschanicum Gymnosporangium torminali-juniperini Gymnosporangium trachysorum Gymnosporangium tremelloides Gymnosporangium tsingchenense Gymnosporangium turkestanicum Gymnosporangium unicorne Gymnosporangium vauqueliniae Gymnosporangium yamadae
References
Other sources 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