Genetic diversity and propagation of mangroves

• Royal Forest Department, Thailand
• Vietnam National University, Vietnam

Mangrove forests are a well known feature of coastlines in the tropics and subtropics. They are very important in protecting and stabilising coasts in cyclone-prone areas. They act as a nursery for many fish species of economic importance and a habitat for other fauna. They can also be an important resource for local people, providing them with wood and other products. Mangroves are now heavily exploited in many parts of the world. Wood-gathering and fishpond operations are the main threats. Other pressures are mining and mineral extraction, diversion of freshwater (which damages mangrove roots), the development of coastal areas with associated silt and pollution, the construction of channels and harbours, and the disposal of wastes.

About 80 higher plant species, from several different groups, are considered as mangroves. There is thus considerable variety in mangrove forests. This diversity is generally reduced by exploitation or other damaging pressures. Once damaged or destroyed, it is hard to re-establish mangrove forests. The survival rate of seedlings is naturally low, and this difficulty is compounded by a lack of seed availability to establish re-planting programs. It's also important to know what types of mangroves to plant where. If reforestation of degraded mangrove areas is to be successful and appropriate conservation strategies defined, it will be necessary to improve the collection, storage and transport of mangrove germplasm (the seeds) and to understand better the intricacies of mangrove genetics.

Several developing countries have asked ACIAR to help with the problem of obtaining adequate supplies of desirable germplasm to set up mangrove plantations. These requests were the origins of this project.

This project aims to improve our knowledge of the genetic variation existing in selected species of mangroves, and then to produce and disseminate germplasm of high quality varieties. The work is expected to benefit mangrove conservation and reforestation in South and Southeast Asia.

The researchers will assess the amount of genetic variation that exists within and between populations of mangroves. They will then find out to what extent desirable traits are genetically determined, and develop screening and selection procedures to identify desirable mangrove genotypes. In the process they hope to improve existing procedures for propagating mangroves and their germplasm. In conjunction with CIFOR, this project also aims to study the effects of disturbance and habitat fragmentation on the genetic diversity and structure of mangroves. Finally, the research staff will help national authorities transfer results of the project to relevant agencies and communities.

A species readily available to all partner organisations, probably Avicennia marina, will be used for working up the skills necessary for DNA analysis and micropropagation. Once perfected, DNA derived from the leaves of selected mangrove species (most belonging to a genus that is widespread throughout the tropics) will be sequenced to improve knowledge of genetic variation. Distinctive genetic markers will be identified to differentiate provenances and varieties. A specialist will develop the best technique for obtaining aseptic plant tissue samples.

Once all techniques are perfected, germplasm of desirable trees from partner countries will be genetically tested. Micropropagation will produce cloned 'plantlets' which will be distributed for field testing in a range of sites.

Mangrove communities have been heavily exploited for their wood, and disturbed by other activities including aquaculture, mining, and disposal of chemical wastes. This project was established with Thailand to undertake molecular biological studies on genetic variation in mangroves, and Vietnam to develop methods for micropropagation of mangrove through tissue culture.

After two and a half years excellent progress was made in achieving the objectives related to the application of DNA marker techniques to the mangrove Avicennia marina. This research was conducted at Southern Cross University, and was given a head start when important groundwork for the molecular studies of genetic diversity in this species was initiated and supported by Southern Cross University in 1997. The results have been disseminated in several publications in refereed journals, and have raised important questions about population structure, mating systems and gene flow that are currently being addressed in Australia (A. marina) and Thailand (R. apiculata). In Thailand, the collaborators have succeeded in establishing new techniques of DNA analysis with support and training from Southern Cross University. The project has thus clearly contributed to building research capacity in Thailand.

Glasshouse trials of A. marina from different provenances have shown that plants maintain differences in morphological and growth characters when grown in the same environment. This is an important result as it demonstrates that these traits are genetically determined. It still needs to be determined what characteristics are considered desirable for re-establishment of new plantations in specific locations, and the extent to which these can be sought out in natural populations.

A major aspect of the project has been to develop micropropagation of mangroves using tissue culture techniques. However, it has become evident that mangroves (A. marina and Rhizophora spp.) do not respond well in tissue culture. Satisfactory progress has been made at Burringbar NSW and Yen Lap, Vietnam, yet much work remains ahead before routine and efficient micropropagation of desirable genotypes can be achieved. The project has received an 18-month extension.