Puccinia sorghi virulent on sweet corn with the Rp1-D gene in southern France.

The Rp1-D gene, which conveys a chlorotic-fleck resistant reaction to Puccinia sorghi, effectively controlled common rust on sweet corn in North America for nearly 15 years. Biotypes of P. sorghi virulent on plants with the Rp1-D gene were widespread in North America for the first time in 1999 and again in 2000 (1,2). Many Rp-resistant sweet corn hybrids that are developed and grown in North America also are grown in Europe, including France where virulence against the Rp1-D gene has not been reported previously. In September 2000, uredinia of common rust were observed on and collected from sweet corn hybrids with the Rp1-D gene in commercial fields and hybrid trials in the Landes and Pyrenees Atlantiques departments of the Aquitaine region of southwestern France. Severity of rust generally was below 5% on these plants except for a few hybrids for which severity was about 20 to 30%. Common rust was not observed on hybrids with the Rp-G gene. Urediniospores were increased as a bulk population on the suscep...