When does hard coat impose dormancy in legume seeds? Lotus and Scorpiurus case-study.

In many legumes, the germination ability of newly harvested seeds is controlled by two contrasting processes, the maturation process and the establishment of seed coat dormancy, which prevents the germination of mature seeds. These two processes are often staggered, so that seeds may achieve a transitory ability to germinate long before the establishment of seed coat dormancy. To clarify these issues, a field and laboratory experiment was conducted on two Mediterranean legume species, Lotus ornithopodioides L. and Scorpiurus muricatus L. subsp. subvillosus (L.) Thell. [syn. Scorpiurus muricatus L. var. subvillosus (L.) Lam.]. Pods were collected from mother plants at regular intervals from the beginning of seed filling to complete maturation. The seeds harvested at different times were weighed and submitted to germination assays to evaluate their germination ability. The results show that the seeds of L. ornithopodioides and S. muricatus acquired a good germination ability (>70%) already at 27 and 23 d after anthesis (DAA) before reaching their maximum dry weight, while seed coat dormancy was imposed much later for the two species, at 40 and 32 DAA. Based on pod and seed morphology, seed weight, and germination ability, three distinct stages were defined during maturation, which might help identify when seeds achieve their maximum germination ability. This may be a first step in overcoming the problem of seed coat dormancy alongside studies on postharvest treatment of freshly harvested seeds.