The effect of various after-ripening temperature regimens on the germination behaviour of Ambrosia artemisiifolia

Abstract

Ambrosia artemisiifolia (common ragweed) is an annual weed known to infest crops and disturbed areas, and cause human pollinosis. To examine the effect of different thermal regimens on seed germination, during seed after-ripening, a study was conducted for two years. In 2012 (year 1) and 2013 (year 2), ragweed seeds collected from a single wheat stubble field were divided and stored under one of the five temperature regimens: constant −20 °C, +5 °C, room temperature (18 °C), +25 °C, and field conditions. Germination tests were performed every 15 days of storage from day 17 to day 213. Storage conditions showed a strong influence on ragweed seed germination duration. At constant low temperatures (−20 °C), seed behaved in an opposite manner depending on the year; in year 1 germination was inhibited while it was stimulated in year 2. At higher temperatures, seed dormancy was unbroken due to a lack of exposure to low temperatures. Under field conditions, seeds reached a high level of germination after a few days of storage due to temperature fluctuations. The different behaviours of ragweed seeds shown at constant temperatures revealed different dormancy depths in the two years that might be due to population variability and maternal environment differences during seed maturation.