Epidemiology of the septoria disease complex of wheat: effect of cultivar, crop rotation and weather on disease development

The complex of the septoria diseases of wheat, septoria nodorum blotch, septoria tritici blotch and septoria avenae blotch, is economically important in the Parkland region of Saskatchewan. Cultural practices are the only economic means of control. Thus, the objectives of this study were to examine the epidemiology of the septoria disease complex on spring wheat grown in the Parkland region of Saskatchewan and to determine the effects of cultivar, crop rotation and weather conditions on disease development. Cultivars used in this study possessed only low levels of resistance to the septoria complex. However some cultivars were more resistant than others. HY320 and Oslo had the highest levels of resistance, while Park, Kenyon and Roblin had the lowest. Katepwa, Neepawa, Pembina and Columbus had intermediate levels of resistance. Weather conditions were favorable for disease development in July and August of 1987 and severe septoria epidemics occurred. A rotation with one year of summerfallow between wheat crops showed little reduction of disease development compared to continuous wheat. However, a rotation of two years between wheat crops significantly reduced the area under the disease progress curve (ADPC) and significantly increased the time to 50% disease severity (T50) of all cultivars. In 1988, weather conditions were much less favorable for disease development and septaria epidemics were light to moderately severe. Under this lower disease pressure a rotation of one year between wheat crops adequately controlled the disease complex. Crop rotation had a small and inconsistent effect on the apparent infection rates of cultivars in both years. The Septoria species involved in the disease complex were examined by identifying and counting lesions produced by each pathogen. Lesions of S. tritici were rarely observed on the cultivar Oslo indicating that Oslo possesses a fairly high level of resistance to this pathogen. A rotation of two years between wheat crops significantly reduced the number of lesions of S.nodorum. The relative occurrence of S. nonodorum and S. tritici varied with location and year. Few lesions of S.avenae f.sp. triticea were observed. Grain yield and kernel weight at the continuous wheat site was lower than that at the barley or canola stubble sites in 1987. In 1988, the low level of disease and the drought conditions at Shellbrook resulted in little useful yield and kernel weight data. At Weirdale in 1988, a significant yield loss of 12 to 19% occurred with a rotation of continuous wheat or one year between wheat crops. No significant yield loss occurred at the site with a rotation of two years between wheat crops. Kernel weight loss at the Weirdale sites did not appear to be related to disease