Stability of fungicide-variety management strategies for Septoria tritici blotch in wheat: insights from AMMI and GGE biplot analyses across multiple environments.

Wheat is a vital cereal crop globally, and over one-third of the world's population consumes it as a staple food. However, Septoria tritici blotch (STB) (Zymoseptoria tritici), which is among the top ten ranked diseases in wheat, poses a significant threat to global wheat production, particularly in southern Ethiopia, where effective management strategies are scarce. The disease limits wheat productivity, necessitating exploration of alternatives due to limited fungicides and resistant varieties. The interaction between management strategies and environmental factors during the host's growing period is crucial for judicious decision-making in STB management. Normal ANOVA assesses main effects but does not capture management by environment interactions (MEI), necessitating the use of AMMI and GGE models to identify reliable strategies. The study areas, despite variable conditions, remain hotspots for STB epidemics, underscoring urgent intervention needs. The objectives of this study were to evaluate the combined effects of wheat varieties and fungicide application on STB development, agronomic traits, and yield loss while examining MEI across multiple environments. Field experiments were conducted in southern Ethiopia (Burji, Bonke, and Chencha areas) across cropping years (2018-2019). The study employed a factorial arrangement with a randomized block design that included four wheat varieties (Shorima, Hidase, Ogolcho, and Kubsa), three fungicides (epoxiconazole + thiophanate-methyl (EPX + TPM), tebuconazole, and propiconazole) and unsprayed controls, and it was replicated three times. Disease severity, relative area under disease progress curve (rAUDPC), and agronomic traits were analyzed using normal ANOVA and biplot models. Key findings indicated that Shorima + EPX+TPM consistently showed the lowest STB severity (9.41%), rAUDPC (1.58%-days), and highest yield (6.45 t ha⁻¹). AMMI analyses for disease and yield responses across environments exhibited 62.05% and 76.83% of the total variation attributed to management, 27.97% and 2.79% to environmental effects, and 4.51% and 8.33% to MEI effects, highlighting the dominant role of management strategies. GGE biplots identified Shorima + EPX+TPM as the most consistent and responsive tactics across environments. EPX + TPM fungicide spray provided yield advantages of Shorima, Hidase, Ogolcho and Kubsa varieties by 149.76%, 175.65%, 255.74% and 263.28% over unsprayed plots of each variety, respectively. Economic analysis confirmed Shorima + EPX+TPM as the most profitable, with a net benefit of $2678.20 ha⁻¹ and a marginal rate of return of 27.53. In conclusion, integrating Shorima (or Hidase/Ogolcho) with EPX + TPM or Tebuconazole is optimal for STB management, yield enhancement, reducing yield losses, and achieving the highest economic returns in southern Ethiopia and elsewhere with similar agro-ecological conditions. However, the study's limitations include geographic restrictions, a narrow focus on specific wheat varieties and fungicides, and reliance on uncharacterized natural infections, necessitating further extensive research across diverse conditions to provide concrete recommendations for the wider farming community. This work provides a template for sustainable STB management, emphasizing the need for context-specific, integrated approaches in wheat production systems.