Seed dormancy and germination of Heliotropium europaeum L. (Boraginaceae), a Widespread Summer-annual weed

Abstract

Heliotropium europaeum L. (Boraginaceae) is a summer-annual weed of European origin. The aim of this study was to investigate the germination requirements of H. europaeum and to determine if seeds present some type of dormancy. Cold stratification and soaking in gibberellic acid (GA3) were used as pre-sowing treatments for breaking dormancy in H. europaeum seeds. Untreated seeds showed an extremely high dormancy at all tested incubation temperatures (only ≤ 2% of them germinated after 8 weeks of incubation), and GA3 and cold stratification drastically improved germination percentages (≥ 80%). The highest germination percentages of H. europaeum seeds soaked in GA3 were achieved at the highest constant temperature (30ºC) and alternating temperatures (25/15ºC and 30/20ºC). Moreover, the lowest germination rates were observed at the two lowest constant temperatures (15ºC and 20ºC). Germination of seeds soaked in GA3 increased as concentration of acid increased (from 10 to 1000 mg L -1 ). Similarly, cold stratification increased germination at all tested stratification periods (from 7 to 360 days). Since embryos are fully developed and seed mass increased 52% after 24 hours of imbibition, showing that seed coat is water permeable, we conclude that H. europaeum seeds present physiological dormancy. Cold stratification and treatment with GA3 were two effective methods for overcoming the physiological dormancy in seeds of H. europaeum. Knowledge of germination requirements may aid in developing tools and strategies for management of this weed.