Effects of planting date on phenotypic plasticity of Amaranthus retroflexus L.

Amaranthus retroflexus L. is one the most economicaly important invasive weeds in agricultural fields in Turkey. In this work, phenotypic plasticity in A. retroflexus populations grown in common garden environments were investigated. Mature seeds were collected from four naturally occuring populations and the production of F1 progeny were conducted under natural field conditions in Kütahya. Seedlings were planted using a random block design on four separate planting dates; between May and July. Growth and phenological development were recorded, and at harvest the dry weight of vegetative and reproductive tissues were determined. Dormancy and germination potential of mother and F1 seeds were tested on H2O and Gibberellin at 25 and 35 °C. Different planting date revealed phenotypic plasticity in morphological characteristics. Seedlings planted in July had a reduced time to flowering than the ones planted in May. Delayed planting resulted in reduced plant hight, above ground vegetative and reproductive biomass. F1 seeds, like mother populations, showed similar response to temperature and light. Seeds were dormant at 25 °C and dormancy was only released at 35 °C in the light. In addition, dormancy in F1 seeds was effected by the temperature experienced by the mother plant during the generative period. Dormancy level was increased as the mean temperature decreased from flowering to harvest. Amaranthus retroflexus plants showed high plasticity in growth and seed germination behavior in response to different planting date. These results will help to predict how this species will adapt to future climate change.