Selection of Barley for Slow Rusting Resistance to Leaf Rust in Epidemics in Different Severity1

Abstract

Slow rusting resistance is of great potential value because it may be more stable than resistance recognized by infection types. However, the conditions necessary for most effective selection for slow rusting resistance are not well defined. The barley (Hordeum vulgare L.) cultivars Gus, Larker, Vada, Volla, Gold, and the lines MN9062, MN7572 and MN7544, known to differ in slow rusting resistance, were evaluated in the field during severe and mild epidemics of race 4 of Puccinia hordei. The area under the disease progress curve (AUDPC), used to estimate slow rusting, was larger for all cultivars and lines in a severe epidemic than in a mild one. The differences among the eight cultivars and lines for AUDPC were more distinct in the severe epidemic. The ranking of the cultivars and lines according to AUDPC was similar in both epidemics as indicated by Spearman's coefficient of rank correlation (0.86, significant at P = 0.01). It is suggested that selection for slow rusting resistance preferably be done in severe epidemics with the inclusion as controls, cultivars that are known to rust slowly or rapidly.