Maturation temperature regulates germinability and chemical constituents of Scotch thistle (Onopordum acanthium) cypselas

The effects of maturation temperature on germinability and chemical constituents of Scotch thistle (Onopordum acanthium L.) cypselas ( fruits) were determined as part of our ongoing investigation into the causes of intermittent germination in this species. Mature cypselas were collected from plants that were grown under higher (28 or 30 degrees C) and lower (20 or 22 degrees C) temperature regimes in greenhouses in 2000 and 2001. Two collections were made, from early- and late-ripening capitula. Germinability and the amounts of moisture, wax, phenolic compounds, and lignin were determined for cypselas from all collections. Cypselas that matured in the first year had lower amounts of moisture and wax than second-year cypselas, but did not differ in amounts of other components. Cypselas that matured under the higher temperatures generally had lower amounts of moisture, wax, and phenolic compounds, faster germination, and higher germination percentages. Early-matured cypselas had higher amounts of moisture and wax, faster germination, and higher germination percentages, but lower amounts of phenolic compounds. However, maturation temperature and collection date did not affect lignin content. Consistent and significant differences in germination patterns and chemical constituents between cypselas that matured under contrasting temperatures confirmed that maturation temperature altered the germinability of O. acanthium cypselas. Thus, under field conditions, cypselas that mature under low temperatures can have stronger dormancy and exhibit greater intermittency in germination/emergence patterns than those that mature under high temperatures.