Characterization of new sources of resistance to Uromyces viciae-fabae in a germplasm collection of Vicia faba

A collection of 648 accessions of Vicia faba was screened for resistance to faba bean rust ( Uromyces viciae-fabae ). Two distinct types of resistance were identified, both resulting in reduced disease severity (DS) and area under the disease progress curve (AUDPC), but differing in the expression of hypersensitivity. One should be regarded as incomplete nonhypersensitive resistance and the other as incomplete resistance with late hypersensitivity. The hypersensitive resistance, which has not been reported before, was not dependent on temperature or plant age. These two types of resistance were characterized by three macroscopic components of resistance: increased latent period (LP), decreased colony size (CS) and a relatively reduced infection frequency (IF), both on seedlings and on adult plants. LP and CS were the components of nonhypersensitive resistance most highly correlated with DS and AUDPC measured under field conditions. The presence of necrosis was an additional component in the hypersensitive resistant response.