Leaf rust (barley)

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Leaf rust is a fungal disease of barley caused by Puccinia hordei. It is also known as brown rust and it is the most important rust disease on barley.^[1]

Contents 1 Symptoms 2 Disease cycle 3 Crop losses 4 Pathotypes and host resistance 5 See also 6 External links 7 References

[edit] Symptoms

Pustules of leaf rust are small and circular and produce a mass of orange-brown powdery spores. They appear on the leaf sheaths and predominantly on the upper leaf surfaces. Heavily infected leaves did prematurely.

[edit] Disease cycle

In many areas, leaf rust requires green volunteer barley to survive between cropping seasons. However, in areas where the alternate host, the weed, Star of Bethlehem (Ornithogalum umbellatum) occurs, teliospores are able to infect the plant. They then can undergo a sexual reproduction cycle and produce aceiospores which can then re-infect barley.

Leaf rust develops rapidly between 15 and 22 C when moisture is not limiting. Following infection, new pustules and spores may be produced within 8 days. Urediniospores are wind-borne and can be spread long distances. Teliospore development occurs later in the season either within uredial sori or within separate telial sori. The teliospores are thick-walled and can persist between crops. Upon germination, they a promycelium (basidium) with four haploid sporidia (basidiospores). The basidiospores can infect both barley and the alternate host.

In western Canada, where the rust cannot overwinter, and the alternate host is not present, the fungus may be re-introduced annually as the rust moves northward from the southern United States. In eastern Canada, the alternate host is present, however, infection of barley by aeciospores has not been reported.^[2]

[edit] Crop losses

Leaf rust of barley is considered a relatively minor disease in the United States, however, sporadic outbreaks have occurred in the southeastern and midwestern regions of the country.

[edit] Pathotypes and host resistance

Most of the barley cultivars grown in the United States are susceptible to Puccinia hordei. Sixteen major resistance genes (Rph1 to Rph16) have been identified, but only three (Rph3, 7 and 9) have been deployed in commercial cutlivars worldwide.^[3] In the United States, the Rph7 gene effectively controlled the disease for over twenty years. However, in 1993, pathotypes with virulence to the Rph7 resistance gene were identified in Virginia, California and Pennsylvania.^[4]

[edit] See also

• Barley bacterial blight

[edit] External links

US: North Dakota
Australia

[edit] References

1. ^ Mathre, D.E. (1997). Compendium of barley diseases. American Phytopathological Society, 120 pp. 
2. ^ Martens, J.W.; W.L. Seaman, T.G. Atkinson (1984). Diseases of field crops in Canada. Canadian Phytopathological Society, 160 pp. 
3. ^ Brooks, W.S.; C.A. Griffey, B.J. Steffenson, H.E. Vivar (2000). "Genes governing resistance to Puccinia hordei in thirteen spring barley accessions". Phytopathology 90: 1131–1136. doi:10.1094/PHYTO.2000.90.10.1131. 
4. ^ Steffensen, Brian J.; Y. Jin, C.A. Griffey (1993). "Pathotypes of Puccinia hordei with virulence for the barley leaf rust resistance gene Rph7 in the United States". Plant Dis. 77: 876–869.