Seed dormancy and germination ecology of Johnsongrass (Sorghum halepense) in eastern Australia

Abstract Johnsongrass [ Sorghum halepense (L.) Pers.] is a highly invasive, persistent, and problematic perennial weed in Australian cropping systems; however, its germination ecology has largely been inferred from studies conducted outside eastern Australia, where environmental conditions differ markedly. This limits accurate prediction of emergence timing and optimization of management strategies. The objectives of this study were to characterize seed dormancy mechanisms and to quantify the germination and emergence response of two populations of S. halepense from central Queensland to temperature, light, salinity, osmotic stress, and burial depth under controlled conditions. Seeds from both populations exhibited strong primary dormancy, which was partially alleviated by sodium hypochlorite immersion and more effectively by mechanical scarification using sandpaper, indicating that seed coat–related dormancy is the principal barrier to germination. Temperature significantly influenced germination, with no germination at 15/5 C and high germination (>90%) at 25/15 C to 35/25 C under both light/dark and dark conditions, demonstrating that warm temperatures largely override light requirements. Germination declined steadily with increasing sodium chloride (NaCl) concentrations, and the NaCl concentration required to reduce maximum germination by 50% was approximately 173 mM. Moderate water stress −0.2 to −0.4 MPa produced less germination in comparison to the control, while −0.8 MPa greatly inhibited germination (11%). Emergence was highest from shallow burial depths of 1 to 4 cm and declined sharply beyond 8 cm. These results demonstrate that S. halepense recruitment occurs in a range of environmental conditions; however, environmental stresses or deep soil burial may help manage this weed. This study provides regionally relevant information to enhance emergence prediction and inform integrated weed management strategies in eastern Australian cropping systems.