Variation in germination response within Scotch thistle, Onopordum acanthium L., populations matured under greenhouse and field conditions

The effects of two maturation conditions (greenhouse and field) on germination percentages and rates were determined for cypselas (seeds) of Scotch thistle, Onopordum acanthium L. Four collections from each of three populations were tested in 1996 and 1997 (one of the same 1996 populations was used again in 1997, but two were different). Cypselas from all collections were incubated within three days of collection at 25°C and 10°C, for 14 hours light, and 10 hours dark, respectively. In general, cypselas that matured under warmer temperatures (greenhouse) germinated at higher percentages than those that matured under cooler temperatures (field). For example, in the Environmental Sciences Western (ESW) population at least five times as many cypselas from each greenhouse collection germinated than from the comparable field collection. Cypselas that matured early in the season were usually more germinable than those that matured later. However, field-produced cypselas from half of the populations had the opposite trend. Overall, all populations that matured under warmer conditions germinated at higher percentages than those matured under cooler conditions. Germination rates showed no clear trends among collections or between greenhouse- and field-matured cypselas.