Improving seed quality in large-scale production of native seed

The use of native species has been increasingly advocated to achieve the sustainable recovery of degraded areas and in Europe considerable effort has also been invested into grassland restoration using such species. However, little attention has been paid to the evaluation and significance of aspects of the seed quality of native species, which may have implications for the success of these projects. The current research examined three aspects of seed quality in the context of commercial seed production and the use of seed in the restoration of vegetation. Firstly, the effect of plant and seed responses to a range of maternal environments during seed production was examined using the perennial herb Primula vulgaris as a model. Different shading conditions, imposed in the field over two seasons during seed maturation, produced a range of red : far-red light ratios (R:FR) received by the parent plants. The competitiveness of P. vulgaris plants grown in the different environments was evaluated though measurements of plant gas exchange, membrane integrity, leaf chlorophyll concentration, photosynthetic efficiency, specific leaf area and above ground plant biomass; the weight and number of seeds produced was also assessed. This revealed the phenotypic plasticity of P. vulgaris and that growth, competitiveness and seed production were favoured in shaded conditions. Subsequent germination of the harvested seeds at five temperatures (5 – 25oC) and high to low R:FR revealed that there was no effect of shading of the maternal plant on seed quality, either the rate of germination or final germination. In addition, the maternal environment did not affect the subsequent light and temperature requirements for germination. An increased germination capacity in response to a higher R:FR for all maternal environments suggested the potential for seedling establishment under vegetative shade only in the presence of canopy gaps. Secondly, the germination potential and dormancy-breaking requirements of 113 commercially available seed lots of eight European native species was examined. This revealed a wide range in the germination of seed lots within a species and surprisingly low levels of dormancy. Alternative and more rapid methods to the routine germination methods were subsequently developed. A tetrazolium testing protocol was developed that predicted germination of each of the eight native species in only two days. In addition, the electrical conductivity (EC) of seed soak water provided a quick and inexpensive measure of final germination in a day and even within a day. However, its application may be limited to large and exalbuminous seeds, such as Cyanus segetum, which are dominated by the embryo and lack an endosperm. The third aspect of seed quality investigated was its impact on establishment and growth of Rhinanthus minor, a hemi-parasite. Ten seed lots from commercial sources were sown in the field and their germination characteristics were investigated in the laboratory. Field emergence was influenced by both the radicle emergence of each lot and the mean germination time, which is indicative of seed vigour. Seeds from four lots with >90% radicle emergence were then germinated to radicle emergence and sown in pots alongside plants of two host species, Lotus corniculatus and Holcus lanatus. Plant establishment, height and flowering density were evaluated for the hemi-parasite, while plant biomass was measured for both R. minor and its host. A longer lag period (lower vigour) was associated with higher levels of seedling mortality and lower plant vigour, in terms of plant height and biomass accumulation, and was also reflected in the parasitic impact of the seed lots, with the least vigorous seed lot having no impact on the biomass of its host, Lotus corniculatus. These observations highlight that the quality of the seed is significant to the potential use of R. minor as a hemi-parasite.