Dry storage effects on germinability of Scotch thistle (Onopordum acanthium) cypselas

Effects of dry storage under various conditions and durations were determined on the germinability of Scotch thistle (Onopordum acanthium) cypselas. Freshly-matured cypselas of O. acanthium were collected from four and two populations in 1996 and 1997, respectively, and germinated at 25 °C for 14 h in light and 10 °C for 10 h in darkness. Cypselas from the 1996 collection were stored dry under laboratory conditions (20-25 °C) and tested for germination as above after periods of 5, 50, 97, 109 and 170 days. At the end of each germination test, remaining non-germinated cypselas were tested for viability. Cypselas from the 1997 collection were stored dry under laboratory conditions (20-25 °C), outside in an unheated shed (-16 to 33 °C), in a seed room (5 °C) and in a freezer (-20 °C) and then tested for germination under alternating light/dark conditions as above and in constant darkness (25 °C for 14 h and 10 °C for 10 h) after 7, 14, 28, 56 and 112 days. In both years, germination percentages increased with storage duration, with the maximum percentage after 97 days in 1996 and after 56 days in 1997. There were differences in germination percentage and coefficient of germination rate among populations in both years. In 1996, the coefficient of germination rate increased with storage duration until 97 days and then decreased, while in 1997, it decreased with increased storage duration. More than 98% of the cypselas were viable in both years.