Two Components of Slow-Rusting in Asparagus Infected withPuccinia asparagi

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Abstract
Slow-rusting resistance in the field and latent period and number of uredinia per square centimeter of stem surface in the greenhouse were evaluated on several asparagus lines. In two years of observation in the field, rust development (as measured by the area under the disease progress curve) was less on lines 277E .times. 22-8, Jersey Centennial, Delmonte 361, 56 .times. 22-8, and UC 157 than on Mary Washington, Wash T2, and WSU-1. Lines with less rust in the field had longer latent periods and fewer uredinia per square centimeter of stem when inoculated uniformly with urediniospores of Puccinia asparagi in the greenhouse than lines that had more rust in the field. The area under the disease progress curve was negatively correlated with length of latent period (correlation coefficients ranged from -0.60 to -0.91) and positively correlated with number of uredinia per square centimeter of stem (correlation coefficients ranged from 0.71 to 0.92). Asparagus shoots of both slow- and fast-rusting cultivars became more resistant to rust, as indicated by a longer latent period and fewer uredinia per square centimeter of stem, as they matured.