Pathotypes and Host Resistance
Most of the barley cultivars grown in the United States are susceptible to Puccinia hordei. 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. 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. 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.
Read more about this topic: Leaf Rust (barley)
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