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Cedar-Apple Rust

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Gymnosporangium Rusts
telial horns form on branch of witch's broom

Cedar-Apple Rust

telial horns

note chlorotic spots on leaves
Cedar-Apple Rust is caused by Gymnosporangium juniperi-virginianae, a heteroecious, demicyclic rust fungus.

note chlorotic spots on leaves
Infection of apple leaves by basidiospores in the spring results in the development of bright yellow chlorotic spots.

spermagonia develop on upper leaf surface
cross section through a spermagonium

Spermagonia form on the upper leaf surface shown here on the left. On the right is a cross 
section through a spermagonium showing the receptive hyphae and spermatia. 

If fertilization occurs, aecia develop 
on the bottom of the leaf directly beneath the spermagonia.
aecia develop on bottom of leaf

aecia splits to release aeciospores
The aecia splits open at maturity releasing aeciospores which are wind-disseminated to Juniperus species in summer and early fall.


infection of alternate host

Severe infection of the alternate host apple causes not only chlorotic leaf 
spots but also defoliaton and degrade in fruit and fruit production.


Infection of Juniperus needles results in the formation of a gall the year following infection. 

telial horns are formed on galls
The second year following infection of junipers, telial horns are formed on the galls in early spring. 

telial horns
dry weather can dry telial horns up

If wet weather continues during telial formation, telial horns can elongate up to 3 inches and 
become gelatinous in consistency.  If dry weather occurs after telial horns have begun to 
form, the horns can dry up (right) but will resume growth upon the return of wet weather. 

The two-celled teliospores of G. juniperi-virginianae are formed and embedded in the telial horn. Each cell is capable of germinating to produce a basidium and four basidiospores.

Other Gymnosporangium Rusts Found in North Carolina

gelatinous telia of Quince rust
Quince rust is caused by Gymnosporangium clavipes.  The telial stage occurs on juniper, causing a slight swelling of the branches.  Telia of this species are gelatinous and pulvinate or hemispheric. 

The aecia occur on the fruit and stems of the alternate hosts, crabapple, quince 
and hawthorn.

Gymnosporangium nidus-avis causes a witch's broom on juniper with the aecial stage on apple, hawthorn, quince, and other rosaceous hosts.

Gymnosporangium effusum can cause swellings and cankers on juniper trunks as well as branches. The alternate host is chokeberry.
witch's broom

close up of witch's broom

Gymnosporangium ellisii causes severe 
witch's broom on Atlantic white cedar which
may be a factor in forest stand reproduction 
and use as a Christmas tree species.

aecia appear on wax myrtle leaves close up of aecia

The alternate hosts for G. ellisii are wax myrtle (Myrica cerifera) and sweet fern (Comptonia 
peregrina). Here, spring-forming aecia are beginning to appear on wax myrtle leaves.   

telial horns

Small, filiform telial horns are formed on branches of the witch's broom on Atlantic 
white cedar. Teliospores are formed and embedded in these telial horns.

Gymnosporangium globosum causes a small rounded gall on juniper with wedge-shaped gelatinous telial horns. The aecial stage occurs chiefly on hawthorn, but also on apple, pear and mountain ash.

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This website was prepared by Becky Bernard.
Last updated on 04 February 2008 by M.J. Munster