The Race-Specific Resistance Gene to Powdery Mildew, MlRE, Has a Residual Effect on Adult Plant Resistance of Winter Wheat Line RE714

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Abstract
Race-specific resistance genes to powdery mildew have been extensively used in wheat breeding programs, but the complete resistance they provide breaks down when confronted by pathogen isolates with matching virulence. However, when overcome, some race-specific genes have a residual action leading to a reduction of the symptoms. Our objective was to determine if the resistance genes MlRE and Pm4b have a residual effect on adult plant resistance (APR) and on vernalized seedling plant resistance (VPR) in the line RE714. Individuals from two populations (double haploid [DH] and F(3) families) were genotyped for the race-specific genes MlRE and Pm4b and assessed for their resistance under field conditions at the adult plant stage (in 1996 and 1997 for the DH lines and in 1997 for the F(3) families). Vernalized seedlings of the DH population were tested with four powdery mildew isolates. Only the MlRE gene had a significant effect (dominant type) on APR. Neither MlRE nor Pm4b had a significant effect on VPR. The dominant residual effect of the defeated race-specific gene MlRE was a component of APR in the line RE714.