Variability of germination response of European populations of Abuliton theophrasti as a function of seed maturing season.

Inter-population variability regarding dormancy and germination has been considered as part of the adaptive strategy of weeds to spread across areas with different environmental conditions or with frequent anthropic disturbances. Intra-specific variability has been observed among weed populations within the same climatic region as a consequence of specific local environmental and agronomic conditions. Acquiring knowledge about intra-specific variability of the main weeds species could contribute to develop effective and transferable IWM strategies. Seeds of three populations of Abutilon theophrasti Medik. were collected in summer 2008 at three locations: Legnaro (Padova, Italy), Tapada da Ajuda (Lisbon, Portugal) and Arganda del Rey (Madrid, Spain). The three seed batches were sown in autumn 2008 at the CSIC-experimental farm located in Arganda del Rey, so all emerged plants experienced the same maternal environment during their life cycle. Seeds were collected in 2009 in three subsequent moments, called Collection Times (CT 1, 2 and 3), i.e. 9th July, 27th August and 16th October, to compare germination response of seeds produced under different maturing season (i.e., environmental conditions). Nine seed batches were obtained. Mechanical scarification was performed on seeds to facilitate imbibition. Seeds were incubated at different constant temperatures (8, 12, 18 and 22 °C) with 12 h of light. Three 50-seed replicates were included for each treatment. Germinated seeds were counted and removed daily and at the end of the experiment viability of nongerminated seeds was checked with a seed-crushing test. The germination percentage of each replicate was calculated with the total number of viable seeds as a basis. The germination percentage reached maximum values at the central incubation temperatures (12 and 18 °C) while it decreased at 8 or 22 °C. The mean total germination percentages of the three populations reached similar values close to 90 % if results of seed batches with different CT were averaged. Instead, significant differences were detected among the germination responses of seed batches derived from the same populations but collected at different moments. Seed batches CT3 of the Italian population and CT1 of the Spanish one presented lower total percentages of germination (78.1 % ± 2.34 SE and 81.5 % ± 4.55 SE respectively) than the other seed batches from the same populations. These differences increased at the lower and higher incubation temperature with germination percentages of around 70 % for both seed batches. The seed batches CT3 Italian and CT1 Spanish were therefore probably characterized by a higher level of dormancy than the other seed batches produced at different moments by the same populations or at the same moment by different populations. The highest and most constant germination response was obtained by CT2 for the Italian and Portuguese population and by CT3 for the Spanish one. Further studies are required to asses if the observed variability represents part of the adaptive response of the three populations to their specific local environmental conditions.