Application of a Rank-Based Method for Improved Cultivar Selection in Soft Red Winter Wheat

Lackermann, K. V., and Esker, P. D. 2011. Application of a rank-based method for improved cultivar selection in soft red winter wheat. Plant Dis. 95:1407-1413. Both grain yield and disease performance are important factors to consider for winter wheat (Triticum aestivum) cultivar selection. However, disease severity and yield data are often presented separately, making it difficult to compare values across multiple environments. The objective of this study was to use a rank-based method to compare cultivars based on yield and disease performance combined across multiple environments. Thirty-six wheat cultivars were planted at each of four Wisconsin locations (Arlington, Chilton, Janesville, and Lancaster) in 2009 and 2010. Plots were assessed four times during the growing season for powdery mildew, Septoria/Stagonospora leaf blotch, and leaf rust. Incidence and severity of Fusarium head blight were assessed at Zadoks growth stage 85 (soft dough). Within each location–year, cultivars were ranked for severity of each disease and for grain yield. One-way analysis of variance was performed to calculate an overall rank value that incorporated data for all four diseases and yield across the eight location–years. There was an effect of cultivar on overall rank (P < 0.0001). Powdery mildew rank was strongly correlated with overall rank (Spearman’s rho = 0.485, P = 0.005), as was yield rank (Spearman’s rho = 0.674, P < 0.0001). Cultivars described as “best” or “worst” cultivars were generally more consistent in their rankings across different measures. The use of a rank-based method provides an approach that will allow growers to base cultivar selection on multiple performance measures across multiple environments. In Wisconsin, soft red winter wheat (Triticum aestivum L.) production has more than doubled over the past 10 years in response to increasing monetary value and greater worldwide demand (24). Annually, global yield losses due to wheat diseases in the field or in storage are estimated to be 20% (3). Although, for many wheat producers, the primary method of disease management during the growing season is the application of a foliar fungicide, these applications carry both economic and environmental costs (4,13,25). For this reason, the primary tactic a producer should consider is the selection of high-performing cultivars, as measured by both grain yield and disease resistance. By planting wheat cultivars with excellent disease resistance, growers may be able to offset the need for fungicides during the growing season. However, a number of factors may make it difficult for growers to assess the quality of available cultivars. First, there is insufficient data about the importance of wheat diseases and their impact on cultivar performance. Second, the incidence of disease is unpredictable and highly variable from year to year. Although wheat diseases commonly occur in Wisconsin, the severity of each disease varies from year to year and across locations (18) Finally, although location and local environmental conditions have been shown to influence disease severity and cultivar performance, environmental conditions are also unpredictable and highly variable among years, even within the same location (10,18,29). Due to the variation in disease pressure in different locations, it is important for growers to know which cultivars perform well against a variety of common diseases across multiple environments. Cultivar selection is often based primarily on the yield performance of the cultivar. If disease performance is considered, typically only one or two diseases are included in the evaluation of the cultivar and it may be the disease that was most problematic in the previous growing season. However, overall performance is a function of both the genetic potential of the cultivar and the unpredictable physical characteristics of the field environment. When growers make cultivar selections based on performance at only one location or look at the reaction of the cultivar to only one disease, they are betting that environmental conditions will be the same and