Variation for Rust Resistance Within Asparagus Cultivars. Dennis A. Johnson, Associate and Extension Plant Pathologist, Washington State University, Research and Extension Center, Prosser 99350. . Plant Dis. 73:309-312. Accepted for publication 31 October 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0309.

Nine to 15 individual asparagus plants from each of five cultivars and one breeding line were selected for differences in latent period when infected with Puccinia asparagi. Plants were increased by crown division. Clones of five cultivars were tested for length of latent period and number of uredinia per linear centimeter of stem after being inoculated uniformly with P. asparagi in the greenhouse. Clones of six cultivars were tested for resistance as measured by the area under the disease progress curve (AUDPC) 2 yr in the field. Latent period varied significantly for clones within four cultivars, number of uredinia per linear centimeter of stem varied significantly for clones within only one cultivar, and AUDPC varied significantly for clones within all six cultivars both years. Latent periods of individual juvenile plants and AUDPC were not correlated, but mean latent periods of mature clones were negatively correlated with AUDPC in two of five cultivars and the combined cultivars. Number of uredinia per linear centimeter of stem was positively correlated with AUDPC in one of five cultivars. Values for AUDPC were significantly (P = 0.01) correlated the 2 yr. Considerable heterogeneity for rust resistance existed within open-pollinated and clonal hybrid asparagus cultivars. Progress in developing more highly resistant cultivars should be possible using selected germ plasm from commercial asparagus cultivars. The AUDPC of replicated asparagus clones in the field during severe rust epidemics would be beneficial in selecting for resistance.