Performance and Stability of Winter Wheat Cultivars to Stagonospora Nodorum Blotch Epidemics in Multi-Environment Trials

Field performance of winter wheat genotypes with quantitative resistance to Stagonospora nodorum blotch is influenced by genotype-by-environment interactions (GEI). This phenomenon explains why cultivars may perform inconsistently across environments, affecting decisions on locally adapted varieties. Further, GEI can also impact risk assessment when cultivar reaction is used as a model predictor under the assumption of stability of responses across environments. Thus, this study investigated GEI effects on four disease metrics; final disease severity (SEV), relative area under disease progress stairs (rAUDPS), time to 50% disease incidence (T 50 ) and the apparent rate of disease increase (ω), describing SNB epidemics of 18 commercial soft red winter wheat cultivars planted in 18 environments in North Carolina from 2021 to 2024. Linear mixed models with various variance-covariance structures for random effects were used to analyze the disease data and a 3rd order factor analytic model provided the best fit to the data across the metrics examined. Type B genetic correlation (r g ), broad-sense heritability (Hb^2), overall cultivar performance (OP), and global stability (RMSD), were estimated using model outputs and the factor analytic selection tool method. For SEV, rAUDPS and T 50 , values of r g ranged from -0.15 to 0.99 with most environment pairs exhibiting high r g values indicating an agreement in cultivar rankings. Cultivar ‘USG 3230’ was the top-performing and most stable, while ‘TURBO’ and ‘SH7200’ were more unstable cultivars. Cultivar reaction classes derived from OP exhibited consistent class-level means of marginal predictions supporting their utility as stable indicators of SNB susceptibility in risk assessment models.