Fungicide strategies and modeling yield losses for managing septoria leaf blotch and brown rust on durum and bread wheat in Moroccan arid and semi-arid regions

Septoria leaf blotch (SLB) and brown rust (BR) are the major wheat diseases in Morocco. This study aimed to estimate yield losses due to these diseases and develop a simple and easy-to-use yield loss model in wheat based on AUDPC, fungicide and genetic resistance. The experiment was conducted during two cropping seasons at two experimental sites and included trials to develop and validate yield loss models. Treatments included A0 (control), A1 (single fungicide application), and A2 (two applications) of propiconazole (1 L/ha). SLB predominated in the first cropping season, while BR was predominant in the second. The fungicide treatments effectively reduced disease severity, with A2 consistently outperforming A1. Disease severity reductions were more pronounced in susceptible varieties, and resistant varieties exhibited minimal yield losses despite significant disease reductions. Yield losses caused by SLB were 19% and 28% compared to A1 and A2, respectively, while those caused by BR were 16% and 19% compared to A1 and A2, respectively. The yield loss models developed herein related grain yield (GY) Y to disease development X as the Area Under the Disease Progression Curve (AUDPC). During the first cropping season, SLB models were Y = 39.74–6.80e-10 X³ (R²=97%) at Sidi El Aidi and Y = 29.43–5.08e-9 X³ (R²=94%) at Jemaat Shaim. In the second season, the BR model was Y = 35.65–1.69e-9 X³ (R²=91%). Disease severity assessed at GS 53 in Jemaat Shaim, GS 70 in Sidi El Aidi for SLB, and GS 71 for BR, were the most predictive stages for estimating yield losses. These findings emphasize integrated management strategies combining fungicides and genetic resistance to reduce yield losses. The models provide practical tools for managing SLB and BR in Moroccan wheat systems.