Effects of blast on components of wheat physiology and grain yield as influenced by fungicide treatment and host resistance

Two field experiments (Exp. 1 and Exp. 2) were carried out to assess the physiological performance and grain yield of wheat cultivars BR‐18 (moderately resistant) and Guamirim (susceptible) inoculated with Pyricularia oryzae in plots treated or untreated with Ópera (fungicide 13.3% epoxiconazole + 5% pyraclostrobin). Results from regression analyses indicated that spike and leaf blast severity at 10–14 days after inoculation (dai) were associated with greater yield losses (highest negative slope) than severity at 18–22 dai. Relative to untreated Guamirim, there were 0.3% and 16% increases in Exp. 1 and 2, respectively, for untreated BR‐18 (resistance alone). For fungicide treatment alone, the mean yield of Guamirim increased by 20% and 61% in Exp. 1 and 2, respectively, relative to the untreated fungicide control, whereas for the fungicide treated BR‐18, the mean yield increased by 26% and 83% in Exp. 1 and 2, respectively. Fungicide application and cultivar resistance resulted in higher measures of leaf health and photosynthetic performance in both spikes and leaves than in the untreated susceptible reference treatment. The results from this study may be useful in future efforts to develop crop loss models and management guidelines for wheat blast.