Crown Rust

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Puccinia coronata is a fungal plant pathogen that requires two hosts to complete its life cycle. It has a broad primary (telial) host range, including more than 45 genera of grasses, and a narrow alternate (aecial) host range, mostly Rhamnus (buckthorns), but also Berchemia (supplejacks) and Elaeagnus (silverberries or oleasters). It is an economically important disease on cereals and grasses, including cultivated oats, barley, and rye.

There are many varieties of Puccinia coronata and all of them are species specific for their primary host. Each variety can be distinguished only on the primary host, and each is identified by that host. Collectively they are referred to by the common name Crown Rust. Two well known varieties are Oat Crown Rust (Puccinia coronata var. avenae) and Barley Crown Rust (Puccinia coronata var. hordei).

On infected grass plants Crown Rust appears as light orange, pustule-like structures (uredinia) on the upper and lower leaf surfaces. It will occasionally also appear on leaf sheaths, culms (stems), the stalks of inflorescences (peduncles), and awns.

The uredinia are the fruiting structures of the fungus. They are round to oval and up to 3 ⁄16″ long. They contain a dusty mass of thousands of microscopic, orangish-yellow summer spores (urediospores).

On common buckthorn Crown Rust first appears as swollen, yellowish-green spots on the upper leaf surfaces, leaf stalks (petioles), and twigs. Leaves and twigs are disfigured but the infection is not fatal to the plant.

More than 45 genera of grasses, including oat, barley, rye, quackgrass, slender wheatgrass, western wheatgrass, foxtail barley, and common buckthorn

Early May to September

The life cycle of Crown Rust includes five stages and requires two host species to complete. The five stages are teleoispore, basidiospore, pycniospore, aeciospore, and urediospore.

First stage: Winter spores (teliospores), also called resting spores, overwinter on the remnants of infected wild grasses and on the residue of infected agricultural grasses left in the field.

Second stage: In the early spring, the teliospores germinate and produce summer spores (basidiospores). The basidiospores are wind blown up to a half mile. Some are eventually deposited on the upper leaf surface of young leaves of the alternate host, common buckthorn.

Third stage: In early May, bright yellow spots appear on the upper leaf surface. Each spot contains flask-shaped reproductive structures (pycnia) below and breaking through the upper leaf surface (epidermis) of the leaf. The pycnium is an aerial vegetative body made up of cluster of branching, receptive filaments (hyphae). The pycnium releases spores (pycniospores) in a thick, sweet liquid which attracts insects. The pycniospores are carried by insects or splashed by rain to the receptive hyphae of another nearby pycnium.

Fourth stage: The fertilized pycnia produces a raised, orangish-yellow “cluster-cup” (aecium) on the lower leaf surface. The aecium releases aeciospores which are carried on air currents.

Fifth stage: Aeciospores that land on an alternate host develop into a another kind of spore-producing body (uredium). Within 7 to 10 days asexual spores (urediospores) are formed and released. The urediospores are carried by gravity or wind to other plants and other parts of the same host plant. Generation after generation of urediospores are produced throughout the growing season, continually reinfecting the plant or crop. At the end of the growing season teliospores are produced and the cycle begins again.

Sources

4, 7, 24, 26, 29, 30.

Widespread and very common

Orange-Yellow Rust

I was hiking in Apple Blossom Overlook Park near La Crescent yesterday. I spotted the fungus on a Buckthorn. Don’t know the species of rust, probably Puccinia coronata var. avenae. A bit or research says that it also affects wheat and oat crops. Too bad, it would be great if it only hit Buckthorn.

Location: 2427 Dallman Lane SE Rochester Mn 55904

please provide advice. Thank you.

Crown Rust disfigures the leaves and stems on which it is found. However, it is not fatal to the plant.

In some cities, Burnsville MN is one, the city encourages homeowners to pull up common buckthorn. Buckthorn is an undesirable, invasive, non-native plant that crowds out our native species. If your buckthorn has some crown rust on it, this may be a good time to get rid of it.

Location: Apple Blossom Overlook Park

I was hiking in Apple Blossom Overlook Park near La Crescent yesterday. I spotted the fungus on a Buckthorn. Don’t know the species of rust, probably Puccinia coronata var. avenae. A bit or research says that it also affects wheat and oat crops. Too bad, it would be great if it only hit Buckthorn.