Gymnosporangium Rust

Leaf Rusts of Hardwoods and Needle Rusts of Conifers

Cedar - Apple Rust - Gymnosporangium juniperi-virginianae

Cedar - Hawthorn Rust - Gymnosporangium globosum

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Pycnia on top surface of apple and hawthorn leaves.

Pycnia on leaves

The small dots on this hawthorn leaf are pycnia. These will produce pycniospores in pycnial fluid that attacts insects.

Pycnia and insect on leaf

Pycnia of Gymnosporangium on apple leaf with pycnial fluid and insect that is attracted to the sweet fluid. Insects move the pycniospores from one leaf to another and bring pycniospores from one mating type to the opposite mating type on another leaf. 

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After fertilization, new hypahe with two nuceli per cell grow through the leaf and produce aecia on bottom of leaf.

Aecia on leaf

Another view of the aecia showing their tubular structure. The aecia are filled with aeciospores. These spores are wind diseminated and infect nearby junipers.

cedar apple gall

After infection with cedar-apple rust, galls form on the juniper. The following spring the telial columns or telial horns are formed. Telia can be seen just starting to emerge from the gall.

Telia on gall

Telia expand during wet weather in the spring.

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Telial horns expanding.

Telia expanded when wet

Telial horns contain teliospores that remain in the telia and are not disseminated. 

Telia cedar apple rust

A fully formed and expanded group of telia on juniper.

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The teliospores of Gymnosporangium are two celled. These spores produce a basidium-like structure that produces 4 basidiospores.

Teliospores cedar apple rust

Teliospores producing basidia and basidiospores. You can see the two celled teliospores, basidia coming out of a teliospore and lots of small oblong basidiospres.

Quince Rust - Gymnosporangium clavipes

Quince rust on hawthorn

Aecia on the fruits of Hawthorn caused by Quince Rust. In Minnesota, Hawthorn serves as a host for this rust (in the south, quince serves as a host). On ornamental hawthorn infection occures mostly on the fruits where pycnia and aecia are formed.

Quince rust aeciospores

Aeciospores are produced inside the tube-like aecia on the hawthorn fruit. Pycnia form before and can be seen on the fruit in the background (small dots).

Quince rust on juniper

On junipers, the telia of Quince Rust are produced on swollen infected stems and even the main mole of the junipers.

Telia quince rust

Telia of Quince Rust produced on a swollen branch.

X-sec of runt infected juniper

A cross section of a juniper limb infected with Quince Rust. The rust can persist in the juniper branch or main stem for years causing swellings and cankers.

Another species of Gymnosporangium produces a broom rust on junipers. This is presented on the "Broom Rust Web Page"