Cytogenetical test to predict the vigour potential in brassica seeds under long-term storage.

Preservation of intraspecific diversity in seed banks is a common strategy to frontier the loss of biodi- versity, however long-term storage inevitably results in the loss of a certain percentage of seeds, there- fore causing the genetic erosion of a seed collection. For this reason seed quality monitoring is of out- standing importance to ensure that the regenerated genetic material is representative of the endemic nat- ural diversity once reintroduced in the environment, as well as to preserve the genetic biodiversity of species economically relevant for modern agriculture. Ageing amplification tests, in which seeds under- go osmotic stresses, enable to detect little differences in the vigour of seeds with high germination per- centage (%G) thereby allowing to predict precociously damages induced by long-term storage. In the present research the quality of Brassica villosa subsp. drepanensis seeds stored in a genebank (at - 20°C for sixteen years) was compared to seeds at harvest (control) by combining %G and mean germina- tion time (MGT) measurements, ageing amplification tests and cytogenetic changes in primary roots. Comparison of %G and MGT between control and stored seeds showed no significant differences. Conversely ageing amplification tests where a saline shock (NaCl -0.9 MPa) was given for six hours to control seeds or after storage, evidenced no significant influence on %G of control seeds, but sig- nificantly reduced the % G of stored seeds. The treatment with 1.4 MPa osmotic potential significant- ly reduced %G of control and stored seeds (50 and 4% respectively). Cytogenetic analysis clearly showed significant reductions of the mitotic index, the appearance of c – metaphases, chromosomes laggings and bridges in stored seeds in respect to control seeds germinat- ed in water. While the treatment with -0.9 MPa osmotic potential had no significant effects in both groups, the treatment with -1.4 MPa osmotic potential had inhibitory effects in root apices of control seeds and completely prevented cell division in stored ones. The results presented in this study indicate that despite a comparable germinative response of seeds, long-term storage induces cytogenetical damages and increase susceptibility to salt stress, therefore lowering the seed quality. We suggest the use of the ageing amplification test and cytogenetical parameters as more sensi- tive, reliable and inexpensive methods compared to germination percentage tests, allowing an early prediction of genetic erosion events in germplasm banks and representing a valuable alternative tool for seed producers