In the field
Seeds use dormancy to hold off germination until the environment becomes suitable, that is, when the surrounding conditions are going to give the seed the best chance at life. This might mean, for example, that there is water present, that a sunlight gap has formed in the canopy, that nutrients are suddenly available such as after a fire or when the seed is defecated after being eaten by an animal. Sometimes dormancy occurs to prevent all the seeds from germinating at once! Dormancy may reduce the proportion of viable seeds that germinate at any one time, increase how long germination takes to begin, or prevent the seeds from germinating entirely. We need to understand what type of dormancy a seed has so that when we want to germinate seeds we know how to break it.
In the laboratory
In the laboratory, we use a number of different techniques to break seed dormancy which include scarifying (cutting/scratching) the seed coat, temporary cold or warm stratification (storage), repeatedly rinsing seeds, soaking the seed in hot water or concentrated acid, soaking the seeds or germinating them in the presence of the plant hormone gibberellic acid or smoke water. One technique alone may be suitable, or two or three may be used together, but multiple things are tried until the highest proportion of germination is found. Below is a graph of germination results from an experiment in which groups of seeds of Hibbertia glabrescences subsp puberula were each treated differently.
Germination of Hibbertia glabrescences subsp puberula following different pre-treatments and incubation conditions. Seeds were germinated on either water agar (WA) or gibberellic acid agar (GA) and then incubated at either a constant temperature of 20°C, or alternating day and night temperatures of 25 then 10°C. Some groups also had a 2% solution of smoke water added to the agar. Seeds were inspected every few days with cumulative germination (germination %) recorded.
Our viability and germination testing hopefully results in the production of new rainforest seedlings. As seeds germinate they are removed from experiments, potted up and grown on in the nursery. These plants can then serve new roles, forming the basis for tissue culture material or living collections. Material can be planted into our Gardens or even donated to other organisations.
Seedlings generated during the Rainforest Conservation Project donated to Illawarra Landcare.