Robust needlegrass Achnatherum robustum (native to the central Rocky Mountains, USA) is a perennial reaching 1.5 m in height. It has great potential for use in erosion control and restoration plantings. Overcoming seed dormancy can however be a problem in Achnatherum species. This study investigated germination in the laboratory of robust needlegrass at various constant and alternating incubation temperatures.
Seeds were collected from populations in Utah (1998 and 1999) and Nevada (1999). Trials were conducted in the dark (robust needlegrass seeds are adapted for self burial, suggesting germination occurs in darkness). Seeds were placed on germination paper in Petri dishes and kept moist with tap water.
Treatments (4 replications of 25 seeds each) comprised 55 constant or alternating incubation temperature regimes:
1) Constant incubation temperatures of 0, 2 and 5° C, and 5° increments up to 40° C.
2) Alternating regimes of 16 h at each constant temperature, plus 8 h at each higher temperature per 24 h (e.g. 35° C alternated with 40° C only; 0º C alternated with 2, 5, 10, 15, 20, 25, 30, 35 and 40° C).
Germination counts (seeds were considered germinated when the radical emerged 5 mm) were made at 1, 2 and 4 weeks incubation.
Seeds were found to germinate at a wide range of constant and alternating temperatures. At least some germination occurred in 76% (Nevada seed) to 89% (Utah seed) of the temperature regimes tested.
Highest germination occurred at 15 to 20°C warm periods alternating with 0 to 20°C cool periods (46% Utah 1998; 76% Utah 1999; and 78% Nevada seed). These are considered ‘moderate’ seedbed temperatures. The only constant temperature to produce similarly high germination was 20°C.