Seed dormancy in Amaranthus retroflexus L. collected from natural populations

Amaranthus retroflexus L. is one of the most common weed species in agricultural fields in Turkey. In this study, the dormancy status of seeds of A. retroflexus was investigated. Mature seeds were collected from naturally occuring populations in Bandırma/ Balıkesir, Bursa, Kütahya and Ulubey/Uşak in 2014. Seed dormancy and germination potential were tested on H2O (at 25, 30, 35 and 40 °C) and GA3, GA4+7, KNO2 (at 25 and 35 °C) in both continuous dark and light conditions. Seeds remained dormant at all tempertaures in the dark on H2O. In the light, dormancy was only released when seeds were incubated at 35 °C. This indicates a requirement for both light and high temperature (35 °C) to release dormacy. GA4+7 was more effective than GA3 in releasing dormancy. In the presence of GA4+7 germination at 25 °C in the light was higher than in the dark and showed differences between populations. The highest germination at 25 °C was recorded in seeds from Uşak. In the dark at 35 °C, GA4+7 replaced the light requirement with all populations germinating more than 80%. The response to KNO2 at 25 °C in the dark also revealed differences between populations. The Kütahya population was the most responsive to KNO2. Germination in all populations in the presence of KNO2 was over 80% at 25 °C in the light and at 35 °C in the darkness. In addition, dry after ripening of seeds was also effective in releasing dormancy. 2014 was one of the hottest years of the 21st century in Turkey and globaly. The annual local temperature data for 2014 allows the localities, where seeds were collected, to be ranked from low to high average temperature (Uşak < Kütahya < Bandırma < Bursa). The differences in seed dormancy level of the A. retroflexus populations are discussed in relation to the climate conditions experienced by the mother plants. Key words: Amaranth sp, dormancy, global warming, redroot pigweed, weed.