Leaf rust is a fungal disease of barley caused by ''

Puccinia hordei ''Puccinia hordei'' is a species of rust fungus Rusts are plant diseases caused by pathogenic fungi of the order Pucciniales (previously known as Uredinales). An estimated 168 rust genera and approximately 7,000 species, more than half of whi ...

''. It is also known as brown rust and it is the most important rust disease on barley.

Symptoms

Pustule A skin condition, also known as cutaneous condition, is any medical condition that affects the integumentary system—the organ system that encloses the body and includes skin, nails, and related muscle and glands. The major function of this sy ...

s of leaf rust are small and circular, producing a mass of orange-brown powdery

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

s. They appear on the leaf sheaths and predominantly on the upper leaf surfaces. Heavily infected leaves die prematurely.

Disease cycle

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.

Pathotypes and host resistance

Most of the barley

cultivar A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture, ...

s grown in the United States are susceptible to ''Puccinia hordei''. Nineteen seedling resistance genes (i.e. ''Rph''1 to ''Rph''19) have been identified, but only three (''Rph''3, 7 and 9) have been deployed in commercial cutlivars worldwide. In the United States, the ''Rph''7 gene effectively controlled the disease for over twenty years. However, in 1993, pathotypes with virulence to the ''Rph''7 resistance gene were identified in Virginia, California, and Pennsylvania. Recently, the first simply inherited gene conferring adult plant resistance to leaf rust in barley was designated ''Rph20''. ''Rph20'' originated from the two-rowed barley landrace ''H. laevigatum'' (i.e., ''Hordeum vulgare'' subsp. ''vulgare''); parent of the Dutch cultivar 'Vada' (released in the 1950s). To date there have been no reports of an ''Rph20''-virulent pathotype.

External links

US: North Dakota

References