Different plant provenance same seed tolerance to abiotic stress: implications for ex situ germplasm conservation of a widely distributed coastal dune grass (Uniola paniculata L.)

Preservation of genetic diversity within germplasm repositories represents an important tool for plant conservation. However, seeds must tolerate extreme levels of post-harvest desiccation and cold to realize benefits of ex situ storage. Factors including local climate and habitat impact expression of desiccation and freezing tolerance especially for widely distributed species. Our aim here was to understand the influence of a latitudinal gradient on seed desiccation and cryo-freezing tolerance. We sampled mature U. paniculata seeds from two geographically and genetically distinct populations then examined seed-water relations and germination following desiccation via equilibrium drying assays (0.5 to 91% RH; -797 to -12.9 MPa). Germination ability after drying and subsequent cryo-freezing treatments (-196 A degrees C, 1 to 1440 min) was also evaluated. Seeds of both populations displayed similar reverse sigmoid moisture sorption isotherms characteristic of desiccation tolerant tissues. Furthermore, initial seed water potential (-63 and -90 MPa) was considerably lower than the lethal limit (-20 MPa) identified for desiccation sensitive tissues. Final germination (range 58-93%) and temporal patterns differed significantly between populations following desiccation and cryo-freezing stress, but these germination responses were similar to initial germination. A higher proportion of non-germinated, yet viable seeds remained for the northern compared to southern population. Location does influence germination response, but differential germination is related to seed dormancy rather than desiccation or cryo-freezing sensitivity. Ex situ conservation of U. paniculata is therefore feasible across the latitudinal gradient studied here.