Breaking physical dormancy in seeds – focussing on the lens

Abstract

○The influence of seasonal factors on the germination of impermeable seeds of Fabaceae was studied. Seeds of 14 herbaceous species were buried for up to 2.5 yr and exposed to natural seasons. At regular intervals, seeds were exhumed and germination was tested in four different temperature regimes. Some species had a very low percentage germination regardless of season, others germinated predominantly in the autumn. Six species showed a marked seasonal cycle with high germination percentages in spring and very low percentages in other seasons. The results of the burial experiment were similar to the pattern of seedling emergence in field conditions. ○ High percentage germination in spring could be simulated in controlled conditions for Melilotus albus, Medicago lupulina, Lotus corniculatus, Trifolium pratense and T repens. Seeds of T. pratense had a high percentage germination after cold treatment, whereas seeds of the other four species were brought to germination by chilling for 8 wk followed by exposure to daily alternating temperatures (15/6°C or 20/10°C). Without previous chilling, these seeds did not respond to the alternating temperatures. ○At least for some legume species, a combination of temperature treatments may act as a signal for seeds and induce water uptake and germination. If the temperature requirements are not fulfilled, seeds remain impermeable and dormant until the next favourable season.