Molecular biology and pollination as a tool to enhance the long-term viability of the Sunshine Diuris orchid, Diuris fragrantissima.

A project undertaken at the Zoological Parks & Gardens Board, Melbourne, Victoria, and supervised by P Temple-Smith

Background

Now critically endangered, the Sunshine Diuris, an endemic to Victoria, was once abundant on the grassy plains west of Melbourne (Fig.1). The virtual wild extinction of this species (only one plant remains in the wild), has been caused by habitat destruction and degradation (Fig.2).  The remaining population faces threats from weed invasion, predation by introduced herbivores, lack of or wrongly timed fire and illegal collection (Fig.3). 

A key objective identified in the revised Recovery Plan was the establishment of several self-sustaining populations of this orchid in the wild. The ex situ population of Sunshine Diuris at Melbourne Zoo and the Royal Melbourne Botanic Gardens was established for re-introductions of this species to the wild.

The research program outlined below was commissioned to determine the genetic fitness of the ex situ population to meet this objective (Fig.4).

Significance of problem

Prior to this research, approximately 200 plants were held and propagated by institutions, including Melbourne Zoo, and community based growers. However with no provenance records readily available, and a limited founder population, the relatedness of the plants was not clear.

This genetic information is key to the successful recovery of this species because of our complete reliance on an artificial breeding program to provide new stock.

Description of project action

The aim of this project is to contribute knowledge that will increase the likelihood of successful reintroduction of the Sunshine Diuris and other native orchid species by:  

1. identifying the genetic relatedness and variability of the current managed population and using this information to maximise long-term viability through careful reproductive strategies.
2. using genetically selected stock of the Sunshine Diuris to increase diversity within the current population.
3. investigating the effects of relatedness on reproductive success.

Cooperation with other institutions and local communities

• Royal Botanic Gardens Melbourne
• University of Melbourne
• Australasian Native Orchid Society
• Native Orchid Growers Network
• Endangered Victorian Orchids Recovery Team

The Royal Botanic Gardens Melbourne is a joint research partner in this project.

Project results and ongoing commitment

Genetic Analysis

Morphological measurements and genetic analysis using allozymes and AFLP’s have all identified a higher than expected level of genetic diversity (Fig.5).  This data has been used to devise a breeding program to increase plant numbers while minimising the risk of inbreeding.  These techniques are also applicable to other ex situ populations of threatened orchids.

Breeding system

The results of this study demonstrate that the Sunshine Diuris is self-compatible, so fruit set is not limited by self-pollination (Fig.6).  It remains to be seen whether this seed has a lower viability or seedlings resulting from self pollination are less successful than those resulting from cross-pollination.  The lack of fruit set in unpollinated plants confirms that flowers do not mechanically self-pollinate and that a pollen vector is required.  This is an extremely important finding because it has implications that need to be taken into account for the re-establishment of a self-sustaining wild population.

Morphology

Morphological analysis found a striking diversity of morphological traits within the flowers of Sunshine Diuris (Fig.7).

Implications & ongoing commitment

The genetic information obtained in this study is important for the species recovery program because of the reliance on artificial breeding to provide new stock. Genetically significant plants have been identified and breeding strategies implemented to maximise their representation in the population.

The genetic diversity that is still present in the ex situ population provides a good base for the breeding program and future translocation of the Sunshine Diuris.  This, combined with knowledge of the composition and ecology of its former locations, will help to improve the recovery of this species. 

Zoos Victoria will continue to implement the breeding program for the Sunshine Diuris and develop strategies, with the Orchid Recovery Team, for the successful reintroduction of this species to the wild.