Ex situ conservation of Caladenia: photoautotrophic micropropagation of Caladenia – Progress Report

Progress report on the grant:

Rob Cross of the Royal Botanic Gardens Melbourne, supervising Honours students Gayle Marven and Anne Lucas Department of Ecology and Evolutionary Biology, Monash University

Progress Report November 1997

As a part of an integrated conservation project, the Royal Botanic Gardens has been able to propagate threatened Caladenia species using in vitro symbiotic germination techniques, with the ultimate aim to reintroduce these plants Into their natural habitat. However, the survival rate of plantlets ex vitro has been less than ten percent. Many studies offer explanations for poor survival rates of micropropagated plants, including the effect that the micropropagation environment has on the anatomy, physiology and biochemistry of the plant.

Changing the in vitro environmental conditions in which the plantlets are grown, may offer a solution to this problem. Increasing light levels and maintaining carbon dioxide levels in the atmosphere for the in vitro plants (that is, photoautotrophic micropropagation), and using different support media In the flask, have been shown to Increase plantlet survival for some species.

Assessment of modified in vitro conditions for symbiotically germinating Caladenia species is continuing. Unexpectedly, it has been found that photoautotrophic conditions reduced the percentage germination for Caladenia seed when compared with non-photoautotrophic conditions. Trials have indicated that this was due to the Inhibitory effect of light on the growth of the associated mycorrhizal fungus. Trials assessing modifications to the flask environment that allow adequate light for the growing plantlets, but shield the fungi from the light have been undertaken. Further trials are planned to complete this appraisal.

The Fog house
In the light of the Australian Flora Foundation Board’s concern that a research area in the foghouse may be overtaken by other non-research projects, a different approach to providing glasshouse conditions for in vitro propagated plants was taken resulting in a better outcome than was originally proposed.

With the grant from the Society for Growing Australian Plants Maroondah Group through the Australian Flora Foundation we have been able to complete the following works:

Minor changes to the existing foghouse, which included the ability to divide the house into two areas one where fog is constantly maintained by the central system, and the other where fog levels can be kept at a lower level This was achieved by the fitting of stopcocks in the supply line to the fogger nozzle, and by reinstalling the sensor in the foghouse in a more appropriate position.

The purchase of a fog tent from C & M Innovations including an ultrasonic fogger. The overall result is:

1. that we can now provide three different fog levels in the foghouse where originally we could only provide one;

2. that the conditions In the fog tent can be varied – for example we can reduce relative humidity levels slowly over time which may assist in the acclimatisation of ex vitro plants

3. that the fog tent very clearly defines an area for research in the foghouse.

We are very pleased with the outcome, and wish to thank the Society for Growing Australian Plants and the Australian Flora Foundation for their support and ideas.