Puccinia coronata

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Puccinia coronata infection on oat
Author(s): Howard F. Schwartz, Colorado State University
Source: IPM Images

Puccinia coronata Corda 1837 - (crown rust)

The fungus causes a serious rust disease of oats in many temperate regions around the world. Other cereals (e.g. barley) and grasses can also become infected by different formae speciales or varieties (see list below). Serious outbreaks develop mainly on oats and barley. On oats, yield losses of up to 25% have been estimated for susceptible cultivars under high disease pressure. In Canada, yield losses were on average about 5% between 2001 and 2005.

The symptoms are characterized by small, bright orange spore pockets on the leaves. The fungus has to go through an obligatory passage on a secondary host, usually a species of the genus Rhamnus like R. catharica (common buckthorn). The use of resistant cultivars is the main approach for managing the disease. However, break down of resistance has been a re-occurring problem. This is facilitated by the fungus undergoing sexual recombination on the alternate host. On barley P. coronata typically overcomes resistance within 5 years.

Vernacular names
• Deutsch: Haferkronenrost
Haferrost
• English: oat rust, oat leaf rust
crown rust of oat
• Español: roya coronada de la avena
• Français: rouille couronnée

During the summer, the fungus spreads from the alternate host to the cereal host through the air, where it forms orange urediniospores which can re-infect other cereals or grasses. The urediniospores are nearly spherical with a diameter of around 20 µm. Near the end of the season, black telia with teliospores are produced. The latter are club-shaped with two cells and about 40-60 x 15-20 µm large. They overwinter on plant debris. During the spring they produce haploid basidiospores which infect the alternate host. On the alternate host, the fungus undergoes a sexual reproduction and forms acia with aeciospores (around 20 µm in diameter) which again infect the primary cereal host.

Numerous formae speciales and varieties have been described, important ones are:

  • Puccinia coronata var. avenae - oat leaf rust and crown rust
  • Puccinia coronata f. sp. bromi - on smooth brome grass
  • Puccinia coronata var. hordei - on barley
  • Puccinia coronata f. sp. lolii - on perennial ryegrass