Cedar–apple Rust
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''Gymnosporangium juniperi-virginianae'' is a plant pathogen that causes cedar-apple rust. In virtually any location where
apple An apple is a round, edible fruit produced by an apple tree (''Malus'' spp.). Fruit trees of the orchard or domestic apple (''Malus domestica''), the most widely grown in the genus, are agriculture, cultivated worldwide. The tree originated ...
s or crabapples (''
Malus ''Malus'' ( or ) is a genus of about 32–57 species of small deciduous trees or shrubs in the family Rosaceae, including the domesticated orchard apple, crab apples (sometimes known in North America as crabapples) and wild apples. The genus i ...
'') and eastern red cedar (''
Juniperus virginiana ''Juniperus virginiana'', also known as eastern redcedar, red cedar, Virginian juniper, eastern juniper, red juniper, and other local names, is a species of juniper native to eastern North America from southeastern Canada to the Gulf of Mexico an ...
'') coexist, cedar apple rust can be a destructive or disfiguring disease on both the apples and cedars. Apples, crabapples, and eastern red cedar are the most common hosts for this disease. Similar diseases can be found on
quince The quince (; ''Cydonia oblonga'') is the sole member of the genus ''Cydonia'' in the Malinae subtribe (which contains apples, pears, and other fruits) of the Rosaceae family. It is a deciduous tree that bears hard, aromatic bright golden-yel ...
and hawthorn and many species of
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 as far south ...
can substitute for the eastern red cedars.


Symptoms

On the apple tree, the infections occur on leaves, fruit and young twigs. The brightly colored spots produced on the leaves make it easy to identify. Small, yellow-orange spots appear on the upper surfaces of the leaves, anytime from April to June. These spots gradually enlarge and turn orange or red and may show concentric rings of color. Drops of orange liquid may be visible on the spots. Later in the season, black dots appear on the orange spots on the upper leaf surface. In late summer, tube-like structures develop on the undersurface of the apple leaf. Infected leaves sometimes drop prematurely, particularly during drought conditions or when the tree is under additional stress. Infections on fruit are usually near the blossom end and are somewhat similar to the leaf lesions. On the eastern red cedar host, the fungus produces reddish-brown galls from to 2 inches (6 to 50 mm). After reaching a diameter of about , the galls show many small circular depressions. In the center of each depression is a small, pimple-like structure. In the spring these structures absorb water during rainy periods and elongate into orange gelatinous telial horns that are 10–20 mm long. The wind carries the microscopic spores to infect apple leaves, blossoms, fruit and young twigs on trees within a radius of several miles of the infected tree. On other species of juniper more common in landscaping and
bonsai Bonsai (; , ) is the Japanese art of Horticulture, growing and shaping miniature trees in containers, with a long documented history of influences and native Japanese development over a thousand years, and with unique aesthetics, cultural hist ...
, the sizes of the infections are reduced. Early in the infection, the galls are small bumps on the woody portions of the plant. They maintain the orange gelatinous form after the first warm rains of spring but generally on a greatly reduced scale.


Disease cycle

Cedar apple rust is caused by the fungi ''
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 Amy ...
'' or more specifically ''Gymnosporangium juniperi-virginianae'' that spend part of their life cycles on
Eastern Red Cedar ''Juniperus virginiana'', also known as eastern redcedar, red cedar, Virginian juniper, eastern juniper, red juniper, and other local names, is a species of juniper native to eastern North America from southeastern Canada to the Gulf of Mexico an ...
s growing near orchards. The complex disease cycle of cedar apple rust, alternating between two host plants, was first delineated by
Anders Sandøe Ørsted Anders Sandøe Ørsted (21 December 1778 – 1 May 1860) was a Danish lawyer, politician and jurist. He served as the Prime Minister of Denmark in 1853–1854. Biography He studied philosophy and law at the University of Copenhagen and was ...
. When exposed to the first warm rain of spring, the small bumps on the galls absorb water, swell, and produce telial horns –gelatinous masses that produce
teliospore Teliospore (sometimes called teleutospore) is the thick-walled resting spore of some fungi (Rust (fungus), rusts and Smut (fungus), smuts), from which the basidium arises. Development They develop in ''telium, telia'' (sing. ''telium'' or ''telio ...
s. When swollen, teliospores will germinate and produce
basidiospore 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 Ploidy () is the number of complete sets of chromos ...
s which are forcibly discharged and travel along air currents to infect apple trees and other alternate hosts. The telial horns will dry out once the rain passes and will lose their gelatinous appearance, instead resembling dark brown threads. When the rain returns, the horns will swell again. This process can repeat eight to ten times during the spring. It can take as little as four hours for basidiospores to form inside the telial horns under optimal conditions. Wind carries the spores to apple leaves at about the time that apple buds are in the pink or early blossom stage. Upon reaching apple buds or leaves covered by films of water, the spores attach themselves to the young leaves, germinate, and enter the leaf or fruit tissues. Light infection can take place in as little as two hours under favorable conditions. Heavy infections take at least four hours to develop. Lower temperatures delay infection. Yellow-orange lesions develop on the upper sides of leaves or on fruit one to two weeks following infection. These lesions contain pycnia and pycniospores. These lesions will produce a sticky honeydew like substance to attract insects that assist in the transport of the pycniospores to different lesions, allowing for sexual recombination. One to two months later, in July and August, orange-yellow aecia are produced in concentric rings on the bottom of the apple leaves or surrounding the pycnia on the fruit. The aecia produce
aeciospore 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 p ...
s. The wind carries the spores back to eastern red cedars, completing the infectious cycle. The spores land on cedar needle bases or in cracks or crevices of twigs. There, they germinate and produce small, green-brown swellings about the size of a pea.
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. Plant galls are abnormal outgrowths of plant tissues, similar to benign tumors or war ...
s do not produce spores until the second spring. However, mature galls usually are present every year. This fungus produces four out of five of the spores known to be produced by the class Urediniomycetes during its life cycle. (These include
teliospore Teliospore (sometimes called teleutospore) is the thick-walled resting spore of some fungi (Rust (fungus), rusts and Smut (fungus), smuts), from which the basidium arises. Development They develop in ''telium, telia'' (sing. ''telium'' or ''telio ...
s,
basidiospore 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 Ploidy () is the number of complete sets of chromos ...
s, spermatia (also called
pycniospore Pycniospores are a type of spore found in certain species of rust fungi. They are produced in special cup-like structures called pycnia or pynidia. Almost all fungi reproduce asexually with the production of spores. Spores may be colorless, gre ...
s), and
aeciospore 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 p ...
s. The type of spore it does not produce is
urediniospore Urediniospores (or uredospores) are thin-walled spores produced by the uredium, a stage in the life-cycle of Rust (fungus), rusts. Development ''Urediniospores'' develop in the uredium, generally on a leaf's under surface. Morphology *Uredinio ...
s.) Rust fungi have a complicated life-cycle with up to five types of spores (each borne on a different type of structure) in its life cycle and often an alternate host, and an "alternate alternate host" as well. Basidiomycetes that have all 5 spore stages and those with less are said to be "macrocyclic" or "microcyclic" respectively.


Control

Because apples are an economically important crop, control is usually focused there. Interruption of the disease cycle is the only effective method for control of the cedar apple rust. Removing as many cedar trees within close proximity of an apple orchard will reduce potential sources of inoculum. The closer the tree to the orchard the greater impact removal will have. Removing all junipers within the 4–5 miles (6.5–8 km) would provide complete control of the disease. Additionally, pruning and disposing of galls from infected cedar trees would reduce sources of inoculum for infection of apple trees, however this would likely be time consuming and uneconomical. For those doing bonsai, it is common to have the trees within feet of each other and on the central eastern seaboard of the United States, eastern red cedar is a common first-growth
conifer Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...
along roadsides. There are differences in the susceptibility of various apple varieties. 'Jonathan', 'Rome Beauty', 'Wealthy', 'Stayman', 'Jonafree' and 'York Imperial' are susceptible. 'Grimes Golden', 'Red Delicious', 'Winesap', 'Redfree', 'McIntosh', 'Liberty', and 'Priscilla' are resistant. Crabapples are generally more susceptible than apples. Resistant crabapples include 'Adams', 'Beverly', 'Candied Apple', 'Dolgo', 'Donald Wyman', 'Eleyi', 'Inglis', 'Indian Summer', 'Liset', 'Mt. Arbor', ''M. persicifolia'', 'Red Jewel', 'Robinson', 'Robusta', 'Royalty', '' M. sargentii'', 'Tina', 'Snowdrift', and 'Special Radiant'. Resistant ''
Crataegus ''Crataegus'' (), commonly called hawthorn, quickthorn, thornapple, Voss, E. G. 1985. ''Michigan Flora: A guide to the identification and occurrence of the native and naturalized seed-plants of the state. Part II: Dicots (Saururaceae–Cornacea ...
'' (Hawthorn) include '' C. crus-galli'', series ''Intricatae'', '' C. laevigata'', '
Autumn Glory Autumn Glory (''Malus domestica'' 'Huaguan') is an apple cultivar developed by growers based in Washington state, US and released in 2011. The fruit is grown by Domex Superfresh Growers with a production of about 56,000 trees as of November 201 ...
', '' C. phaenopyrum'', '' C. pruinosa'', '' C. viridis'', and 'Winter King'. The resistant varieties are less susceptible to attack, but that does not mean that they are free from an aggressive attack. Fungicide sprays applied in a timely manner are highly effective against the rust diseases during the apple cycle. Most protective fungicide sprays are applied four times at 7- to 10-day intervals, starting with pink bud on crabapples. These applications are to protect the apples from spores being released from the cedar host in mid-spring. If cedar apple rust disease is diagnosed on apple fruits and leaves it is far too late to spray. Although curative fungicides also exist for cedar apple rust, they must still be applied before trees begin to develop symptoms. Systemic fungicides are available as well, which require fewer sprays during the season. However, there are no fungicides available to home gardeners that can be used on trees that produce fruit which will be eaten by people.


Gallery

File:Gymnosporangium-juniperi-virginianae.jpg, Another gall on eastern redcedar (''
Juniperus virginiana ''Juniperus virginiana'', also known as eastern redcedar, red cedar, Virginian juniper, eastern juniper, red juniper, and other local names, is a species of juniper native to eastern North America from southeastern Canada to the Gulf of Mexico an ...
'') File:Cedar-apple rust 3.jpg, Close-up on a telial horn: It is full of teliospores (visible as tiny orange spots) File:Cedar-apple rust 4.jpg, Two-celled
teliospore Teliospore (sometimes called teleutospore) is the thick-walled resting spore of some fungi (Rust (fungus), rusts and Smut (fungus), smuts), from which the basidium arises. Development They develop in ''telium, telia'' (sing. ''telium'' or ''telio ...
File:Cedar apple rust heavily infected leaf underside.JPG, Cedar apple rust on a crab apple showing stomata File:Cedar apple rust showing stomata.jpg, Cedar apple rust on a crab apple showing stomata File:Cedar apple rust on shimpaku juniper.JPG, Cedar apple rust on a shimpaku juniper File:Cedar apple rust on J. procumbens nana.JPG, Cedar apple rust on a ''J. procumbens 'Nana File:Gymnosporangium juniperi-virginianae gall sprouting.png, Gall with
telial horns Telium, plural telia, are structures produced by rust fungi as part of the reproductive cycle. They are typically yellow or orange drying to brown or black and are exclusively a mechanism for the release of teliospores which are released by wind ...


References


External links


Cedar-Apple Rust, ''Gymnosporangium juniperi-virginianae''
{{Taxonbar, from=Q5625087 Fungi described in 1822 Fungi of North America Fungal tree pathogens and diseases Apple tree diseases Pucciniales Fungus species