Slow rusting and tolerance to rusts in wheat I. The progress and effects of epidemics of Puccinia graminis tritici in selected wheat cultivars

Abstract

The effectiveness of vertical resistance to rusts in wheat as generally employed is short-lived and a more durable form of resistance is required. To examine slow rusting and tolerance, the progress and effects of epidemics of stem rust (Puccinia graminis Pers, f. sp. tritici Erikss. & Henn.) in 45 wheat cultivars have been followed during two seasons. The epidemics in each cultivar have been compared by means of the average disease assessment, area below the disease progress curve, apparent infection rate, and intercept of the logit line, and by pattern analysis. Of these measures, the infection rate was the least valuable, whilst pattern analysis allowed useful grouping of cuItivars with similar epidemic patterns. The cultivars were arrayed on a resistance spectrum and ranged from highly resistant to extremely susceptible, those between possessing various levels of slow-rusting ability. Slow rusting was at a comparatively high level in cvv. Hopps, Dural, Lawrence and Celebration. In contrast cv. Mengavi was shown to be a fast ruster. The danger of developing cultivars, such as Mengavi, with a fast-rusting tendency masked by initially effective vertical resistance is discussed. The effects of the epidemics in each cultivar have also been determined to provide a tolerance index. The percentage reduction in grain-filling period, the logit-line intercept value and the delay to 10% disease relative to a susceptible reference cultivar were the main factors associated with the effect of the epidemics on grain yield.