Optimizing Sowing Dates to Mitigate Covered Kernel Smut (Sporisorium sorghi) Severity and Yield Loss in Grain Sorghum Genotypes

Abstract

Covered kernel smut (CKS), caused by Sporisorium sorghi, is a major constraint to sorghum (Sorghum bicolor) production in hyper-arid regions. This study evaluated the interactive effects of three sowing dates corresponding to the first day of three consecutive months (May, June, and July) and six sorghum genotypes (Giza-15, Dorado, Giza-113, Mecca, Horus and Ahmos) on disease epidemiology, yield stability and economic returns under artificial inoculation during 2023 and 2024. Sowing date significantly influenced disease severity and yield performance. Under inoculated conditions, the optimal sowing date (1st June) resulted in year-specific disease severity index values of 17.28% (2024) and 17.67% (2023), grain yields of 2328.20-2633.85 Kg feddan-1, yield losses of 6.81–9.54% and economic losses of 4170.29-5780.13 EGP feddan-1, consistently outperforming early (1st May) and delayed (1st July) sowings. Significant genotypic variation in resistance was observed. The hybrid Horus exhibited the highest resistance, recording the lowest values of disease incidence (DI; 19.04-19.56%), disease severity index (DSI; 4.58–5.05%) and yield losses (2.79-4.07%). Whereas Giza-15 was highly susceptible, displaying the highest values of DI (38.86-39.24%), DSI (15.69-16.56%) and yield losses (6.18-7.85%). Three-way interaction revealed that combining June sowing with resistant genotypes reduced economic losses by 91.4% compared with susceptible genotypes sown in July, recording 825.73 vs. 9613.89 EGP feddan-1 in 2024. Correlation analyses showed strong negative relationships between DSI and grain yield in 2024 and a near-perfect positive correlation between yield loss and economic loss, indicating that disease severity is an excellent predictor of economic impact. These findings establish that synchronizing sowing dates with favorable environmental windows, alongside the deployment of resistant hybrids, constitutes a highly effective, low-cost strategy for CKS mitigation in arid agricultural systems.