Variability of physical dormancy in relation to seed mechanical properties of three legume species

Many Fabaceae species have a hard and impermeable seed coat that requires scarification for germination. The variability within a batch and between batches of the same species can be very high, resulting in inefficient dormancy breaking. The main objectives of this study were to investigate the variability in hardseededness among four populations of the legume species Medicago polymorpha, Trifolium glomeratum and T. subterraneum, and to evaluate the effect of the best scarification treatments on the mechanical properties of the seed coat. These species have very small seeds that hinder scarification procedures. Different treatments, including sanding and temperature changes, were studied. Results varied among species, and the most efficient treatment for breaking dormancy was determined for each one. For each species, wide variability was observed in the best scarification treatment within and among populations. The effect of the best scarification treatment on the seed coat of each species was examined by means of scanning electronic microscopy (SEM). Evident differences were found in T. glomeratum, as the treatment used was sanding. In T. subterraneum, scarified seeds (by thermal treatment) showed wider hilum opening. No differences were observed in M. polymorpha seeds