Environmental factors regulating Cenchrus spinifex seed germination

Cenchrus spinifex is a problematic summer weed of semi-arid and sandy soils from Argentina. The objective was to determine conditions (temperature, water potential, soil type and water content) and seed status (burs and caryopses fresh recently dispersed and stored) favouring C. spinifex germination. Fresh burs germinated only at 10/24 degrees C (38%), while stored at 10/24 (38%) and 20/35 degrees C (15%) and any water potential. In sandy soils, fresh burs germinated (78 to 83%) under all water contents, while in loamy soils germinated more under field capacity (92%) than saturation (28%). Fresh caryopses germinated at 10/24 (87%) and 20/35 degrees C (82%) and stored caryopses at any temperature regime (constant or alternate) or water potential. Fresh caryopses germinated on sandy (86%) and loamy (95%) soils at different water contents. Stored caryopses germinated more (89%) than stored burs (21%), independently of temperature or water regime. Fresh caryopses germinated more than fresh burs independently of soil type and water content, indicating the importance of covers on dormancy. Loamy and saturated soils are the worst germination conditions, while limited water availability allows C. spinifex germination, explaining its importance under arid and sandy environments.