The project aims to reduce the effects of diseases that limit productivity of Acacia plantations and build capacity and collaboration on forest health in Indonesia, Vietnam and neighbouring Southeast Asian countries.
Plantation forests of Australian hardwood species in Southeast Asia now exceed 7 million hectares. Diseases and pests threaten the viability of these plantations. Due to tree mortality, growth rates of Acacia mangium in Sumatra in those areas affected by fungal diseases (Ganoderma and Ceratocystis) have been reduced to less than 15 m3/ha/yr, while non-affected areas grow 22 to 35 m3/ha/yr. Ceratocystis is considered an extreme threat in both Vietnam and Malaysia, with up to 20% damage in some Vietnamese acacia plantations.
The research includes aspects of forest silviculture, genetics, biological disease control, forest health surveillance, information technology and extension. Screening for tolerant acacia germplasm and developing biocontrol agents will reduce mortality of acacias caused by Ceratocystis and Ganoderma. Diseases may influence the success of management strategies, so research into these diseases will support the activities.
The project initiation workshop in September 2015 explored the current base of scientific knowledge and the research required to underpin project objectives. This shared understanding of research priorities was further explored by the Ceratocystis workshop in February 2016. This latter workshop attracted 70 participants from 7 SE Asian countries, Australia and internationally renowned invited speakers from Brazil, South Africa and Hawaii. While visiting sites during the workshop field trip in Sumatra it became clear that while the impact of Ceratocystis in Acacia mangium has recently overshadowed that of Ganoderma, the damage caused by this pathogen is a significant component of mortalities. This clear field demonstration heightened the level of interest in finding a biological control agent for Ganoderma.
Both workshops were essential to understanding the risks involved in the screening and breeding activities planned to obtain Ceratocystis tolerant acacia germplasm i.e.
Given the low levels of resistance pure A. mangium may not be an option and it may be impossible to deploy very low levels of resistance in this species (which needs to be reproduced by seed). The initial estimates of resistance in Malaysia for pure A. mangium are low at 5% compared to reports for other acacia species and their hybrids. In Indonesia however A. mangium has the highest productivity and broad adaptability relative to all other acacias and their hybrids and is the preferred commercial species for mineral soils.
Tolerance to Ceratocystis demonstrated in early screening trials must be reflected by later performance in the field especially in A. mangium given that this species has to be planted by seed.
The screening trials in Indonesia will include the screening of A. auriculiformis, potentially to hybridize with A. mangium and increase its level of resistance. Acacia auriculiformis populations have been imported by CFBTI for sowing in late 2016. The A. hybrid seed from the September 2016 FOERDIA collection will be available for sowing in early 2017. Early screening experiments with A. mangium established by RAPP, Sinarmas and MHP in Sumatra, scheduled for artificial inoculation in September/October 2017 will confirm the level of resistance in A. mangium and provide resistant germplasm for subsequent breeding activities.
In Vietnam acacia hybrid acacia clones have been deployed for some time and their development is an integral part of this countries breeding program. Two screening trials with A. hybrid clones have been established in the field at Ceratocystis hot spots with another such trial planned. These field trials will support an early screening trial which has been established in an urban setting and will be artificially inoculated.
A standard operating procedure for artificial Ceratocystis inoculations in resistance screening trials has been agreed to by project partners although the wounding technique (needle or scalpel) may vary between Vietnam and Indonesia due to a difference in tree size to be inoculated.
Different systems of early and rapid screening tests have been tested. It has been demonstrated that the inoculation of phyllodes gives a similar ranking of Ceratocystis host tolerance as observed with pot inoculation trials. Phyllode screening may thus provide a potential early and very rapid screening test of significant interest.
The production methods for the spores of different biological control agents (BCAs) have been improved - we can now produce BCA inoculum reliably and in the quantities needed, although the most competitive BCAs in the laboratory still prove low spore producers. Spores are however more viable in oil but there is low yield when harvesting spores from cultures into oil compared to water.
Three BCA stump inoculation trials (with acacia and eucalypt stumps) have been established to follow the efficacy of spread within the stump and whether the BCA infests the lower part of the stump and associated root debris.
A five hectare compartment size trial with three BCA agents has been established and this activity has highlighted the potential problem of BCA application to stumps at harvest. It has proved very difficult to enter the plantations within 24 hours of harvesting and the stumps are hidden by debris, broken up or squashed into the ground. The only way we may realistically get BCA agents onto freshly cut stumps at a compartment scale is to get them into the chain saw oil or some other immediate delivery mechanism at harvest.
A project website and newsletter has been established. Training and communication activities undertaken during both workshops has had a significant impact and has led to increased networking and knowledge exchange between SE Asian countries. Another major biosecurity risk was presented at the Ceratocystis workshop in an evening session i.e. Puccinia psidii, a rust of Myrtaceous hosts such as eucalypts and a recent incursion into Indonesia. This was new and surprising knowledge for most workshop participants - an unrecognised threat.
The project has made considerable progress towards all of its three objectives during 2016-2017. The first of these objectives is to reduce the impact of Ganoderma root rot disease. The following summarises progress for the investigation of biocontrol-pathogen competition in the laboratory, the development of biocontrol inoculum and its field application and field experiments to test biocontrol efficacy.
Manipulating the BCA and pathogen for testing in the laboratory
Considerable progress has been made in the laboratory towards being able to artificially manipulate and investigate the “pathogen/biocontrol agent” system.
We have already carried out confrontations between the pathogen and candidate BCAs using each type of fungal organism in its mycelial form. This however does not mimic possible interactions on the surface of debris between spores of the pathogen and BCAs.
Unfortunately the pathogen does not reliably produce fruit bodies from which spores could be obtained either in the field or laboratory. But we have found that the pathogen (like the BCAs) can be made to produce asexual spores in culture in the laboratory. These pathogen asexual spores are able to colonise wood. Preliminary co-inoculations have been made on wood to simulate competition between BCAs and pathogens when they meet in nature as spores. This research underpins and informs field investigations.
Tracking BCA growth in stumps
Stump inoculations (acacia and eucalypt) have been set up at 3 field sites to test different BCAs of interest. BCA oidia were applied as aqueous suspensions within 2 hours of felling trees. Trials have been revisited and destructively sampled to track the growth of the BCA (two of the sites have been sampled twice). We are using a combination of culturing and PCR techniques to confirm the extent of stump colonization over time by the BCA species. Mycelia grown from the wood samples harvested has been stored in the freezer and will be identified by DNA analysis by the end of 2017.
Methods for producing, formulating and field application of the biocontrol agent
Progress has been made in reliably producing BCA inoculum in the laboratory and the harvest of oidia from culture into storage under oil.
The semi-commercial trial in which BCAs were applied directly after harvest to stumps has been assessed for root rot disease (and Ceratocystis wilt) when the replanted Acacia mangium was 6 months old. Both diseases were present at very low levels and the trial will be monitored a second time in August 2017.
This trial has raised considerable concerns about the feasibility of treating stumps in the field. This is due to cost and OH&S issues (stumps of manually felled trees have to be treated immediately after felling) and/or the burying of stumps during harvesting so that they cannot be treated with BCAs. Given the barriers to application in the field a third application method will be considered i.e. the potential rhizosphere and/or endophytic colonisation by BCAs of seedling roots in the nursery - before seedlings are planted.
In the previous ACIAR project which initiated the BCA research for Ganoderma root rot disease a trial was established to assess the effectiveness of different BCAs when applied as block inoculum in the planting hole. At two years there are no significant differences between different treatments in the levels of root rot incidence are detected. However there are clear trends that show that certain BCA agents have a lower root rot disease incidence than control treatments. Given that root rot disease does not usually escalate until about 2 years this trial will continue to be monitored.
The second objective of the project is to reduce the impact of Ceratocystis wilt disease. The following summarises progress of screening trials in Indonesia and Vietnam and discusses the development of screening protocols.
Screening A. mangium for tolerance to Ceratocystis
FOERDIA supplied 3 Indonesian industry partners with open pollinated seed from 50 families of A. mangium and the resulting seedlings were clonally replicated for screening. Data was provided from two of the three trials and was analysed simultaneously to provide breeding value estimates for parents, clonal value estimates for progeny and genetic parameter estimates.
In one trial, survival was low at 34.6% but clones with 100% survival were identified (15 resistant clones of 695 evaluated = 2.2%). The second trial presented much greater overall survival at 50.6% percent and 20 of 250 clones had 100% survival (20/250 = 8%).
The clonal replication allowed for a partitioning of additive genetic variance (useful for selection among parents) and total genetic variance (useful for selecting clones). Most of the genetic variance for survival is associated with additive effects, indicating that selection of parents that produce tolerant offspring will be effective in increasing survival ((h2 = 0.19 (+/- 0.04), H2 = 0.21 (+/- 0.04)). However parents selected for tolerance will always have some susceptible progeny.
The small increase in the level of genetic control indicates the repeatability of assessments is low and significant improvements to the screening system need to be made to ensure resistant material can be identified in a single screening. The correlation between parental breeding values was rather low (0.38 (+/- 0.27) and indicates either a low similarity between screening systems or that an interaction between the different inoculum and the parents is present. In summary, while there is a genetic signal for tolerance to Ceratocystis in A. mangium this may not be easily exploitable, its expression being masked during screening by the influence of factors such as plant age, inoculum type and size.
Screening Acacia hybrid for tolerance to Ceratocystis
The Vietnamese screening trial has provided some hope that there is resistance in its acacia hybrid production population, although it is at a very low level. The results have identified 6 tolerant (BV386, BV265, BV474, 33, CLT18, CLT43) and 6 susceptible (93/2, 102, 12, 233/3m BV71, BV73) clones for use in further protocol development experiments. Importantly, parameter estimates from the trial indicates the trial was effective in identifying material with differential levels of tolerance. The repeatability of clonal performance indicates there is some level of genetic control that may be exploited in resistance breeding.
In Indonesia FOERDIA is making progress towards a program for the development and screening of acacia hybrids.
Screening protocol development
Results with screening A. mangium indicate the importance of standardised screening protocols and understanding the influence that different factors such as seedling age and condition, inoculum size and type have on the expression of tolerance. A differential set of A. mangium clones selected from the screening trials is being held by FOERDIA. This material is invaluable and must be used for screening protocol development.
This project has established that phyllodes from different species and clones when inoculated with Ceratocystis demonstrate differential responses in terms of lesion size. This test can be undertaken at a young age, is very rapid and non-destructive, making it an excellent candidate for the early screening of resistance. In Indonesia a good correlation between tolerance and the phyllode test score has been demonstrated. However, in Vietnam the genetic correlation between the damage index and phyllode scores within hybrids was found to be rather low (-0.16) with a slight improvement (-0.21) when pure A. auriculiformis clones were included in the analysis. Further validation of this early screening protocol is taking place in Indonesia and will take place in Vietnam (using phyllode material from the 4 field screening trials established by VAFS).
The third objective of the project focuses on capability building in SE Asia in forest health management. The project still has two training workshops to deliver, one on biological control and another on the remote sensing of forest health information.
A scoping visit was carried out in August 2016 to prepare for the forest health remote sensing workshop in 2018/2019. A training seminar in remote sensing in forestry was given at each of the 3 companies by Christine Stone, NSW DPI followed by discussions with operational staff. We have agreed with RAPP to use the compartment-sized biological control trial site to develop the forest health remote sensing case study for the workshop in 2018/2019. We have acquired images of this sites that can be used to construct a fairly accurate DEM, essential to the success of the case study. In September 2017 a surveyor/UAV expert from UTAS will carry out the first flyover (with a Phantom 4 Pro) to acquire images and also to validate the accuracy of DEM data provided.
The Biological Control workshop will be held on 21-22nd July to coincide with the IUFRO Acacia conference “Towards a sustainable future for Acacia plantations”. Yogyakarta. Approximately 50 participants will attend from all over SE Asia and from Fiji. Crawford funding ($15K) was obtained to support this ACIAR workshop. The workshop will present training in the concepts of biocontrol and its application with specific information from two ACIAR forestry biocontrol projects; FST/2012/091 Biological control of galling insect pests of eucalypt plantations in the Mekong region, led by Simon Lawson and this project). We have also been able to invite an international expert in insect biocontrol Marc Kenis from CABI to present at the workshop.