Seed Pre-Treatments of Native Species for Optimal Germination and Establishment in in-situ Restoration Programmes

(continues from previous...) To conclude, the main results from this study demonstrate that seed performance and responsiveness to treatments among species and more importantly different seed batches of a single species are highly variable. This heterogeneity among seeds can be due to the genetic make-up of the species, the seed maturity stage at collection and the impact of the environment during seed development, maturation and storage, among others. However, seed treatments can in some cases be applied in order to improve seed quality.

In this work I investigate seed quality of wild species and explore seed pre-treatments with the potential to enhance seed performance by assessing seed viability, seed germination and seedling establishment under optimum and stress conditions. Detailed germination experiments have been performed on a range of wild species at seed batch level. Seed were tested under a number of conditions with a set of temperatures, light conditions and additives (active ingredients). Characteristics that were evaluated were final germination, germination speed, uniformity of germination and seedling establishment. Following this, seed treatments with the potential to improve seed and seedling quality were studied to understand the relationship between responsiveness to treatments and the ecology of the species and the provenance and seed maturity of the seed batches. Different compounds with the potential to stimulate seed germination were tested using priming and coating. Primed and coated seeds were tested in various substrates (paper, low nutrient and high nutrient soil) to investigate the suitability of these techniques to improve seed quality of species to be used in restoration. Little is known on tetrazolium testing of wildflower seeds. Therefore, in Chapter 2 a tetrazolium based method was developed in order to quickly assess the viability of seed batches. Moreover, the usefulness of this method for cultivated and wildflower seeds was determined. The number of non-viable seeds in a seed batch plays a large role in the final number of germinated seeds and will determine if seed improving treatments are sensible to be implemented, therefore, assessing seed viability is of remarkable importance. The method demonstrates that grinded seeds are able to reduce tetrazolium if seeds are viable. Hence the intensity of the colouring, generated by a homogenate of seeds is related to the proportion of viable seeds present in the sample. Chapter 3 describes the responses of 23 wildflower species to a wide range of germination conditions. The hypothesis was that species from different habitats will have different germination requirements while species from a similar habitats have comparable ecological requirements. The conditions considered were: variation in light conditions and the absence or presence of nitrate, karrikins or gibberellic acid. The conclusion of this study was that the hypothesis had to be rejected. However, it was observed that species could be grouped by their light response and responsiveness to compounds, which suggested that the habitat required for seeds to germinate may differ from habitat required for plants to complete their life cycle. Seed quality and characteristics are not only determined by genetics (in other words species) but also by time of harvest, production location and after ripening (storage). Hence in Chapter 4 the impact of production locations on seed characteristics is studied. Seed batches of Arabis alpina harvested at different locations are characterised and the effect of priming treatments on germination of the different batches is assessed. The main conclusion is that the germination characteristics of a single seed batch of a species are not representative for the other seed batches obtained for that species and that there is no single treatment that enhances all seed batches of a single species. While in Chapter 4 variations in provenance were considered, in Chapter 5 the impact of harvest time and storage on the quality of primed, coated or untreated seeds is studied. Priming and coating were studied because of their proved usefulness in the seed industry and, thus, their potential in wildflowers. From the results obtained, priming and coating techniques are shown to be able to enhance germination of the wild species studied under optimal and stress conditions; however effectiveness of the treatments varies among seed batches. (continues below...)