Characterization of Resistance to Leaf Rust in Pacific Northwest Wheats

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Abstract
Seven types of resistance to 2 local cultures of P. recondita were identified by determining numbers of uredia/cm2 of leaf surface, length of latent period, number of spores per uredium and infection type (size of uredia and lesions) on seedling and adult plants of 9 Pacific Northwest wheat cultivars. Two cultivars were fully susceptible to both cultures. One cultivar had hypersensitive resistance to one of the P. recondita cultures. The remaining 6 cultivars had various degrees of slow rusting in the field. As measured by the above components, 2 cultivars expressed resistance only in the adult plant stage and 4 expressed resistance in both adult and seedling stages. These 4 cultivars also showed culture .times. cultivar interactions for the above components of resistance, which indicates that slow rusting in them is culture-specific. When cultivars had fewer uredia, longer latent periods and fewer spores per uredium they also had a range of high to low infection types (large to small uredia and lesions). The association between a range of infection types and other components of resistance may be useful for selecting breeding lines that are slow rusting.