MORTALITY AMONG HYBRID POPLAR CLONES IN A STOOL BED FOLLOWING LEAF RUST CAUSED BY MELAMPSORA-MEDUSAE F SP DELTOIDAE

Melampsora medusae Thuem. f.sp. deltoidae was found to be the primary cause of leaf rust in a stool bed, in Westport, Oregon, on 41 hybrid p oplar clones. Each clone was represented by approximately 1000 ramets planted in a block in spring of 1992. Rust severity was rated, using t he Schreiner scale (0-100), on three dates in the fall of 1999: August 28, September 18, and October 28, 1992. Of the 41 clones, 1, 12, and 21 scored 100 (i.e., maximal rust) on the three rating dates, respecti vely. Percent mortality the following spring was estimated for each cl one on May 19. Correlation coefficients for rust severity versus morta lity on the three rating dates were 0.89 (p < 0.0001), 0.85 (p < 0.000 1), and 0.63 (p < 0.0001), respectively. Thus, rust severity and subse quent mortality were highly correlated, especially on the first rating date characterized by maximal infection of the most susceptible clone .