Leaf rust is a fungal disease of barley caused by Puccinia hordei.
[1] Pustules of leaf rust are small and circular, producing a mass of orange-brown powdery spores.
Leaf rust of barley is considered a relatively minor disease in the United States.
Nineteen seedling resistance genes (i.e. Rph1 to Rph19) have been identified, but only three (Rph3, 7 and 9) have been deployed in commercial cutlivars worldwide.
[3] Recently, the first simply inherited gene conferring adult plant resistance to leaf rust in barley was designated Rph20.