Figure 1. Acacia seeds incubated with TZT; good viability in this sample, most seeds have stained bright red indicating metabolic activity, see sectioned seeds and emerging root in intact seeds.
Figure 2. Saltbush Atriplex semilunaris seeds germinating on agar plate, note extending white root from healthy seeds.
Seed viability and germination testing
Native seeds are an expensive and limited resource, and the investments of time and resources required for revegetation and rehabilitation are very substantial. Expensive rehabilitation efforts are wasted if the viability of seeds is sub-standard. We can test seed batches to ensure that they meet the viability and germination rate standards that are required for revegetation projects.
From each batch of seed, replicate samples of 50 to 100 seeds are taken. Seeds are examined and evaluated for physical criteria such as physical damage, insect damage, size, size range and other criteria related to seed health. For viability testing, the standard tetrazolium (TZT) test used for many agricultural seeds can be used. Alternatively, or in addition to this, there will be actual germination testing, this is the best method that gives results most relevant to rehabilitation applications.
Tetrazolium Test (TZT) methodology
The Tetrazolium test (TZT) is used to indicate the percentage of seeds in a sample that are potentially viable and likely to germinate. This is a useful and reliable method that gives a quick result of the theoretical viability and potential for germination. Seeds for testing are hydrated, and then soaked in a solution of TZT for 48 hours. Seeds are scored as viable if they have turned red, indicating biological activity within the seed and embryo tissues. See image.
Germination testing is used to indicate the percentage of seeds that are able to germinate under defined conditions and within a specified time, normally 14-days. Germination is considered to have taken place when there is clear emergence of the seed root radicle from the seed coat.
Germination testing takes 2-4 weeks to complete.
This test is carried out by hydrating a specified number of seeds and then placing them on sterilised agar plates, under controlled temperature and light cycle conditions for the selected testing duration. The healthy seeds will germinate and the percentage of germinated seeds can be calculated by counting germinated seeds compared to non-germinated seeds.
Seeds are scored as having successfully germinated based on emergence of root radicle from the seed, see image.
Figure 3. Higher magnification image of Saltbush Atriplex seeds germinating on agar plate.
Figure 4. Acacia coolgardiensis seeds germinating on agar plate, see white roots emerging from seed tip.
Figure 5. Image of Acacia seeds germinating on agar plate, note small non-viable seeds.