Heart rots in plantation hardwoods in Indonesia and southeast Australia

• Gadjah Mada University, Indonesia
• Centre for Forest Biotechnology and Tree Improvement, Indonesia
• Institut Pertanian Bogor, Indonesia
• Forest and Nature Conservation Research and Development Centre, Indonesia
• CSIRO Forestry and Forest Products, Australia

Fast-growing hardwood plantations are increasingly important to the economies of many countries around the Pacific Rim, including Australia, Indonesia and the Philippines. Although initial emphasis in most countries has been on the market for fibre pulp and paper, there is a significant trend in Australia and other countries (e.g. Brazil) to grow eucalypts for a mix of high- and low-value products.
Acacia mangium plantations throughout Southeast Asia have had limited appeal as a source of higher value products, due to stem defects including extensive heart rot of unknown cause that has resulted in a temporary ban on further plantations of this species in Peninsular Malaysia. Although the impact is primarily on utilisation as sawn products, brown rot fungi (which preferentially degrade cellulose) can also affect pulp yield and market acceptability.
In Indonesia, there are large areas with high capacities for production of wood for sawn products, including timber framing, plywood and veneer. Mills are typically small and labour-intensive and make major contributions to employment in provincial centres. With more than 700,000 ha of recently planted plantations of acacia species already established and much of the native forest resource depleted, it is likely that acacias will be the most widely planted species available to fill the demand for sawn products. The heart-rot problem will be a major impediment to a switch from pulp-log-only harvesting to integration of pulp logs with sawn products. There are also losses due to root rot fungi.
Plantations of Eucalyptus species in southeast Australia mainly comprise E. nitens and E. globulus grown for woodchip export. However, in Tasmania and increasingly elsewhere in Australia, there is a commitment to direct a proportion of the resource toward higher value solid products by thinning and pruning. Initial pruning trials with both eucalypt species have been disappointing at some sites in Tasmania, due to a high level of pruning-associated decay. In southeast Australia experimental farm forestry plantations of A. melanoxylon (blackwood), grown with nurse crops (to enforce apical dominance) and pruned early, have also been subject to discoloration and decay originating from pruned stubs. Research showed that blackwood form and timber quality is very site-dependent, and that provenances must be selected for a particular environment. Thus the factors determining the extent of acacia rot in Southeast Asia and in Australian hardwood plantation trees have much in common.

This project sought to establish the means to minimise impacts of decay on the potential of selected plantation species to produce high-value products.

This project assessed the incidence of root and heart rots in different Indonesian environments. Scientists sought to establish the relationship between silvicultural practices (especially singling multistemmed trees and pruning of A. mangium) and the incidence of heart rot in Indonesian plantations. They also wanted to determine how the incidence/risk of heart rot in pruned and non-pruned stems varied in different environments, also variations between A. mangium provenances, A. crassicarpa and A. mangium x A. auriculiformis hybrids, and between eucalypts selected for other traits such as leaf pathogen/insect resistance and form (single stemming and small branch diameter).
The team developed DNA-based methods coupled with traditional taxonomical and pathological methods to identify and characterise fungi causing rot (in the absence of fruiting bodies) in acacias and eucalypts and to detect their presence in symptomless wood as an aid to the above objective. They also developed guidelines to assist plantation managers in Indonesia to reduce heart and root rot incidence in plantations. Revised selection criteria for tree improvement projects in Indonesia would reflect outcomes of the research.

In developing techniques for the direct detection of fungi from symptomless or rotten wood, approximately 200 new fungal isolates were sequenced using molecular techniques developed during the project - expanding the Fungal Sequence Database and including important decay fungi of the genera Ganoderma, Postia, Trametes etc. Sequences were gained from fungal fruitbodies and isolates collected from both Australia and Indonesia. This populated sequence database increases the likelihood of finding a matching sequence and hence identifying unknown fungi, particularly those isolated from rooted roots, wood or symptomless wood, without needing to locate a fruitbody.
Australian researchers assisted Indonesian staff at the CBFTI laboratory in Yogyakarta with DNA sequencing methodology. Approximately 20 cultures isolated from trees inoculated during a 'wounding trial' were sequenced. A subset sequenced by both the Indonesian and Australian laboratories confirmed the accuracy of the sequencing procedure. The cultures of most interest were isolates of Oudemansiella canarii and Pycnoporus sanguineus - known wood rotters that may be involved in heartrot disease.
Testing the sequence database to identify unknown isolates from rooted and symptomless wood required extraction of DNA from rotting timber. Three different techniques for the direct detection of fungi from wood were attempted, but none produced DNA from the preserved A. mangium wood that was clean enough to amplify and gain a fungal sequence. Recently developed cloning techniques have produced clean fungal DNA from fresh Eucalyptus wood samples, and efforts are under way to adapt the techniques to the preserved A. mangium wood block samples.
A root rot evaluation assessed the increase and spread in root rot over time at the Wonogiri family trial in Central Java. In June 2005, the incidence of root rot at the site had increased by 5.24% since the previous survey in September 2004 and increased by 11.54% since 2003. The increase appears to be linear. It was also noted that 93% of trees classed as alive with Ganoderma sp. fruitbodies in 2003 were dead at the time of the 2005 survey and that the cumulative percentage of trees with fruitbodies is increasing exponentially. If a similar rate of root rot spread was observed in commercial plantations as has been monitored over the last 3 years at this site, preventative and/or early disease management would be considered critical to avoid massive tree and hence economic loss. Results of incompatibility tests that can provide evidence of the means of disease dispersal at a site (due to spore or vegetative growth) indicate that the root rot disease at Wonogiri is currently spreading predominantly via the production of sexual spores.
A workshop titled 'Heart rot and root rot in Acacia plantations: a synthesis of research progress' held at Yogyakarta Indonesia on 7-9 February 2006 attracted a mixture of managers, researchers and technical staff. The workshop enabled casual and formal discussions on the impact and management of heart rot and root rot in Acacia plantations, current research direction and future research priorities.

Laboratory and field manuals in both English and Bahasa were prepared to accompany the laboratory and field sessions of the workshop. During the half-day laboratory session participants learnt to recognise wood rot fungi and undertook fungal isolation and other scientific techniques that assist in fungal identification. During the field visit to the Wonogiri family trial, participants gained experience in scoring logs for heartrot, learnt to recognise both above- and below-ground symptoms of root rot and practiced root rot survey techniques.

Findings of the first 3 years of the project were presented as summary papers at the workshop. These papers, as well as other invited papers, are to be published in both English and Bahasa for circulation to workshop participants and other interested parties.