The germination of seeds is the ultimate measure of viability of any seed collection. It can also be argued that there is little point storing seeds for the future if we don’t know how to germinate them. Therefore successful germination testing is critical to the function of any seed bank. For this reason the TSCC, like other seed bank programs, aims to determine and record the germination requirements for each seed collection it receives (fig. 1).
Petri dishes and agar
The majority of germination tests performed by the TSCC are carried out in 9 cm diameter plastic Petri dishes containing 1% agar-water (a gel of 99% water, fig. 1&2). Petri dishes are stacked inside plastic bags to avoid water evaporation, and these bags are then placed in germination incubators.
Occasionally other compounds are added to the agar gels. Most commonly a very small amount of Potassium Nitrate is added. Very infrequently we have added gibberellins to the germination media. Gibberellins are a group of plant growth regulators (colloquially referred to as plant hormones) that are strongly implicated in the germination process. Our usage of gibberellins is sparing as they are expensive with a limited value in resolving dormancy requirements and are only been used where time/mission critical seedlings of problematic taxa have been required for research purposes.
As of February 2015 the TSCC has ten germination incubators. Six incubators run at 5°C, 10°C, 15°C, 20°C, 25°C and 30°C constant temperatures and the remaining four run at alternating temperature regimes of 12/0°C, 17/05°C, 22/10°C and 27/15°C. Alternating temperature regimes simply attempt to mimic natural day/night temperature fluctuations. Light is provided by fluorescent tubes for 10 hours each day, and in the case of alternating temperature regimes, light will coincide with the warmest temperature. The choice of a 10 hours light /14 hours dark photoperiod was made to roughly approximate day length during the Tasmanian Autumn and Spring period; when we would expect the bulk of seed germination in Tasmania to take place.
To learn more about germination testing read “Germinating seeds for the first time“.
Every seven days the number of germinated seeds is recorded and the percentage germination calculated. This is known as ‘scoring’ and enables germination curves to be plotted at the end of the germination test (fig. 3). On average, a TSCC germination test will run for 56 days, but about 40 % of tests run for up to 112 days, and the occasional test has been known to run for over 20 months.
At the end of a germination test, any non-germinated seeds are assessed using the cut test. Empty or infested seeds are excluded when calculating the overall percentage germination.
In theory, germination percentages should not be significantly different to estimated viability percentages. Viable seeds that do not germinate may possess dormancy.
Once the TSCC have uncovered germination requirements of a collection to achieve greater than 75% germination, the germination test can be repeated approximately every ten years to ensure that the seeds in the seed bank are maintaining their viability.
Once germination tests have been completed all the data is transferred from the paper test sheets to the TSCC database system and the test sheets are then archived. This data is publicly available from the TSCC Germination Database. The germination database is designed to provide you with a summary of all the tests that have been conducted on a collection and their respective successfullness. Searches can be conducted by selecting a plant family or genus.
For information on using our laboratory results in a non-laboratory setting, see interpreting the Germination Database for home use.