Wood properties and processing outcomes for plantation grown African mahogany (Khaya senegalensis) trees from Clare, Queensland (18 and 20 year-old trees) and Katherine, Northern Territory (14 year-old trees).

Khaya senegalensis, African mahogany, a high-value hardwood, was introduced in the Northern Territory (NT) in the 1950s; included in various trials there and at Weipa, Q in the 1960s-1970s; planted on ex mine sites at Weipa (160 ha) until 1985; revived in farm plantings in Queensland and in trials in the NT in the 1990s; adopted for large-scale, annual planting in the Douglas-Daly region, NT from 2006 and is to have the planted area in the NT extended to at least 20,000 ha. The recent serious interest from plantation growers, including Forest Enterprises Australia Ltd (FEA), has seen the establishment of some large scale commercial plantations. FEA initiated the current study to process relatively young plantation stands from both Northern Territory and Queensland plantations to investigate the sawn wood and veneer recovery and quality from trees ranging from 14 years (NT – 36 trees) to 18-20 years (North Queensland – 31 trees). Field measures of tree size and straightness were complemented with log end splitting assessment and cross-sectional disc sample collection for laboratory wood properties measurements including colour and shrinkage. End-splitting scores assessed on sawn logs were relatively low compared to fast grown plantation eucalypts and did not impact processing negatively. Heartwood proportion in individual trees ranged from 50% up to 92 % of butt cross-sectional disc area for the visually-assessed dark coloured central heartwood and lighter coloured transition wood combined. Dark central heartwood proportion was positively related to tree size (R2 = 0.57). Chemical tests failed to assist in determining heartwood – sapwood boundary. Mean basic density of whole disc samples was 658 kg/m3 and ranged among trees from 603 to 712 kg/m3. When freshly sawn, the heartwood of African mahogany was orange-red to red. Transition wood appeared to be pinkish and the sapwood was a pale yellow colour. Once air dried the heartwood colour generally darkens to pinkish-brown or orange-brown and the effect of prolonged time and sun exposure is to darken and change the heartwood to a red-brown colour. A portable colour measurement spectrophotometer was used to objectively assess colour variation in CIE L*, a* and b* values over time with drying and exposure to sunlight. Capacity to predict standard colour values accurately after varying periods of direct sunlight exposure using results obtained on initial air-dried surfaces decreased with increasing time to sun exposure. The predictions are more accurate for L* values which represent brightness than for variation in the a* values (red spectrum). Selection of superior breeding trees for colour is likely to be based on dried samples exposed to sunlight to reliably highlight wood colour differences. A generally low ratio between tangential and radial shrinkages was found, which was reflected in a low incidence of board distortion (particularly cupping) during drying. A preliminary experiment was carried out to investigate the quality of NIR models to predict shrinkage and density. NIR spectra correlated reasonably well with radial shrinkage and air dried density. When calibration models were applied to their validation sets, radial shrinkage was predicted to an accuracy of 76% with Standard Error of Prediction of 0.21%. There was also a strong predictive power for wood density. These are encouraging results suggesting that NIR spectroscopy has good potential to be used as a non-destructive method to predict shrinkage and wood density using 12mm diameter increment core samples. Average green off saw recovery was 49.5% (range 40 to 69%) for Burdekin Agricultural College (BAC) logs and 41.9% (range 20 to 61%) for Katherine (NT) logs. These figures are about 10% higher than compared to 30-year-old Khaya study by Armstrong et al. (2007) however they are inflated as the green boards were not docked to remove wane prior to being tallied. Of the recovered sawn, dried and dressed volume from the BAC logs, based on the cambial face of boards, 27% could potentially be used for select grade, 40% for medium feature grade and 26% for high feature grades. The heart faces had a slightly higher recovery of select (30%) and medium feature (43%) grade boards with a reduction in the volume of high feature (22%) and reject (6%) grade boards. Distribution of board grades for the NT site aged 14 years followed very similar trends to those of the BAC site boards with an average (between facial and cambial face) 27% could potentially be used for select grade, 42% for medium feature grade, 26% for high feature grade and 5% reject. Relatively to some other subtropical eucalypts, there was a low incidence of borer attack. The major grade limiting defects for both medium and high feature grade boards recovered from the BAC site were knots and wane. The presence of large knots may reflect both management practices and the nature of the genetic material at the site. This stand was not managed for timber production with a very late pruning implemented at about age 12 years. The large amount of wane affected boards is indicative of logs with a large taper and the presence of significant sweep. Wane, knots and skip were the major grade limiting defects for the NT site reflecting considerable amounts of sweep with large taper as might be expected in younger trees. The green veneer recovered from billets of seven Khaya trees rotary peeled on a spindleless lathe produced a recovery of 83% of green billet volume. Dried veneer recovery ranged from 40 to 74 % per billet with an average of 64%. All of the recovered grades were suitable for use in structural ply in accordance to AS/NZ 2269: 2008. The majority of veneer sheets recovered from all billets was C grade (27%) with 20% making D grade and 13% B grade. Total dry sliced veneer recovery from the logs of the two largest logs from each location was estimated to be 41.1%. Very positive results have been recorded in this small scale study. The amount of colour development observed and the very reasonable recoveries of both sawn and veneer products, with a good representation of higher grades in the product distribution, is encouraging. The prospects for significant improvement in these results from well managed and productive stands grown for high quality timber should be high. Additionally, the study has shown the utility of non-destructive evaluation techniques for use in tree improvement programs to improve the quality of future plantations. A few trees combined several of the traits desired of individuals for a first breeding population. Fortunately, the two most promising trees (32, 19) had already been selected for breeding on external traits, and grafts of them are established in the seed orchard.

Preservation of encapsulated shoot tips and nodes of the tropical hardwoods Corymbia torelliana × C. citriodora and Khaya senegalensis

Alginate encapsulation is a simple and cost-effective technique to preserve plant germplasm but there are only a few reports available on preservation of encapsulated explants of two highly valuable groups of tropical trees, the eucalypts (Myrtaceae) and mahoganies (Meliaceae). This study investigated alginate encapsulation for preservation of the eucalypt hybrid, Corymbia torelliana × C. citriodora, and the African mahogany, Khaya senegalensis. We assessed shoot regrowth of encapsulated shoot tips and nodes after storage for 0, 3, 6 and 12 months on media varying in sucrose and nutrient content, under storage conditions of 14°C and zero-irradiance. Encapsulated explants of both trees were preserved most effectively on high-nutrient (half-strength Murashige and Skoog) medium containing 1% sucrose, which provided very high frequencies of shoot regrowth (92–100% for Corymbia and 71–98% for Khaya) and excellent shoot development after 12 months’ storage. This technique provides an extremely efficient means for storage and exchange of eucalypts and mahoganies, ideally suited for incorporation into plant breeding and germplasm conservation programs.

Cane Weevil Borer, Rhabdoscelus obscurus (Coleoptera: Curculionidae), a pest of palms in Northern Queensland, Australia

In recent years the cultivation of ornamental palms (Arecaceae) has increased markedly in northern Queensland. Consequently, several insects have become important pests, particularly Rhabdoscelus obscurus (Boisduval), the cane weevil borer. The larvae of this beetle feed on various species of palms, making the plants unsaleable. Death or lodging of the trees may also result. This paper documents its pest status, derived from information in the literature and from consultation with local growers.

The domestication of African mahogany (Khaya senegalensis) in northern Australia.

African mahogany has demonstrated much potential, in many field trials spanning several decades and in furniture manufacturers' evaluations, as a high-value timber species for plantations in northern Australia. It is in the early stages of domestication via a low-intensity, informally-collaborative, mostly-public-sector program of conservation and genetic improvement begun 5 y ago. Silvicultural techniques are being developed through experience in both 'small grower' and larger-scale plantings. See this issue's cover for photographs.

Developing African mahogany (Khaya senegalensis) germplasm and its management for a sustainable forest plantation industry in northern Australia: Progress and needs.

The demonstrated wide adaptability, substantial yield potential and proven timber quality of African mahogany (Khaya senegalensis) from plantings of the late 1960s and early 1970s in northern Australia have led to a resurgence of interest in this high-value species. New plantations or trials have been established in several regions since the early 1990s -in four regions in north Queensland, two in the Northern Territory and one in Western Australia. Overall, more than 1500 ha had been planted by early 2007, and the national annual planting from 2007-2008 as currently planned will exceed 2400 ha. Proceedings of two workshops have summarised information available on the species in northern Australia, and suggested research and development (R&D) needs and directions. After an unsustained first phase of domestication of K. senegalensis in the late 1960s to the early 1970s, a second phase began in northern Australia in 2001 focused on conservation and tree improvement that is expected to provide improved planting stock by 2010. Work on other aspects of domestication is also described in this paper: the current estate and plans for extension; site suitability, soils and nutrition; silviculture and management; productivity; pests and diseases; and log and wood properties of a sample of superior trees from two mature plantations of unselected material near Darwin. Some constraints on sustainable plantation development in all these fields are identified and R&D needs proposed. A sustained R&D effort will require a strategic coordinated approach, cooperative implementation and extra funding. Large gains in plantation profitability can be expected to flow from such inputs.

Gene interactions constrain the course of evolution of phosphine resistance in the lesser grain borer, Rhyzopertha dominica

Phosphine, a widely used fumigant for the protection of stored grain from insect pests, kills organisms indirectly by inducing oxidative stress. High levels of heritable resistance to phosphine in the insect pest of stored grain, Rhyzopertha dominica have been detected in Asia, Australia and South America. In order to understand the evolution of phosphine resistance and to isolate the responsible genes, we have undertaken genetic linkage analysis of fully sensitive (QRD14), moderately resistant (QRD369) and highly resistant (QRD569) strains of R. dominica collected in Australia. We previously determined that two loci, rph1 and rph2, confer high-level resistance on strain QRD569, which was collected in 1997. We have now confirmed that rph1 is responsible for the moderate resistance of strain QRD369, which was collected in 1990, and is shared with a highly resistant strain from the same geographical region, QRD569. In contrast, rph2 by itself confers only very weak resistance, either as a heterozygote or as a homozygote and was not discovered in the field until weak resistance (probably due to rph1) had become ubiquitous. Thus, high-level resistance against phosphine has evolved via stepwise acquisition of resistance alleles, first at rph1 and thereafter at rph2. The semi-dominance of rph2 together with the synergistic interaction between rph1 and rph2 would have led to rapid selection for homozygosity. A lack of visible fitness cost associated with alleles at either locus suggests that the resistance phenotype will persist in the field.

African mahogany. Abstracts from 'Darwin 2011 - African Mahogany Plantation Industry Forum'

This publication summarises the talks presented at ‘Darwin 2011 – African Mahogany Plantation Industry Forum’ held at the Department of Resources Research Facility, Berrimah, Darwin, 31st August and 1st September 2011. The forum brought together a vast amount of experience and knowledge about African mahogany and its prospects as a plantation timber tree in the dry tropics of northern Australia. The abstracts and references represent a valuable body of knowledge building on that recorded in previous African mahogany workshops in Mareeba (2004) and Townsville (2006). Besides the presenters’ abstracts, this publication provides a list of all the authors and their contact details and a complete list of all the cited references and further reading.

Rapid microsatellite marker development for African mahogany ( Khaya senegalensis, Meliaceae) using next-generation sequencing and assessment of its intra-specific genetic diversity.

Khaya senegalensis (African mahogany or dry-zone mahogany) is a high-value hardwood timber species with great potential for forest plantations in northern Australia. The species is distributed across the sub-Saharan belt from Senegal to Sudan and Uganda. Because of heavy exploitation and constraints on natural regeneration and sustainable planting, it is now classified as a vulnerable species. Here, we describe the development of microsatellite markers for K. senegalensis using next-generation sequencing to assess its intra-specific diversity across its natural range, which is a key for successful breeding programs and effective conservation management of the species. Next-generation sequencing yielded 93943 sequences with an average read length of 234bp. The assembled sequences contained 1030 simple sequence repeats, with primers designed for 522 microsatellite loci. Twenty-one microsatellite loci were tested with 11 showing reliable amplification and polymorphism in K. senegalensis. The 11 novel microsatellites, together with one previously published, were used to assess 73 accessions belonging to the Australian K. senegalensis domestication program, sampled from across the natural range of the species. STRUCTURE analysis shows two major clusters, one comprising mainly accessions from west Africa (Senegal to Benin) and the second based in the far eastern limits of the range in Sudan and Uganda. Higher levels of genetic diversity were found in material from western Africa. This suggests that new seed collections from this region may yield more diverse genotypes than those originating from Sudan and Uganda in eastern Africa.

African mahogany (Khaya senegalensis) plantations in Australia - status, needs and progress

The Australian African mahogany estate comprises over 12,000 ha of industrial plantations, farm-forestry plots and trials, virtually all derived from Africa-sourced wild seed. However, the better trees have given high-value products such as veneers, high-grade boards and award-winning furniture. Collaborative conservation and improvement by the Northern Territory (NT) and Queensland governments since 2000 realised seed orchards, hedge gardens and genetic tests revealing promising clones and families. Private sector R&D since the mid 2000s includes silvicultural-management and wood studies, participatory testing of government material and establishing over 90 African provenances and many single-tree seedlots in multisite provenance and family trials. Recent, mainly public sector research included a 5-agency project of 2009-12 resulting in advanced propagation technologies and greater knowledge of biology, wood properties and processing. Operational priority in the short term should focus on developing seed production areas and ‘rolling front’ clonal seed orchards. R&D priorities should include: developing and implementing a collaborative improvement strategy based on pooled resources; developing non-destructive evaluation of select-tree wood properties, micropropagation (including field testing of material from this source) to ‘industry ready’ and a select-tree index; optimising seed production in orchards; advancing controlled pollination techniques; and maximising benefits from the progeny, clone and provenance trials. Australia leads the world in improvement and ex situ conservation of African mahogany based on the governments’ 13-year program and more recent industry inputs such that accumulated genetic resources total over 120 provenances and many families from 15 of the 19 African countries of its range. Having built valuable genetic resources, expertise, technologies and knowledge, the species is almost ‘industry ready’. The industry will benefit if it exploits the comparative advantage these assets provide. However the status of much of the diverse germplasm introduced since the mid 2000s is uncertain due to changes in ownership. Further, recent reductions of government investment in forestry R&D will be detrimental unless the industry fills the funding gaps. Expansion and sustainability of the embryonic industry must capitalise on past and current R&D, while initiating and sustaining critical new work through all-stakeholder collaboration.

First report of shoot blight of persimmon caused by Diaporthe neotheicola in Australia

Shoot blight symptom was found on persimmon (Diospyros kaki) in southern Western Australia in December 2010. The pathogen was isolated and identified as Diaporthe neotheicola on the basis of morphology, sequence analysis of the internal transcribed spacer (ITS) and the translation elongation factor 1-α (TEF). A pathogenicity test was conducted and Koch's postulates were fulfilled by re-isolation of the fungus from diseased tissues. This is the first report of D. neotheicola causing shoot blight on persimmon in Australia and worldwide. © 2012 Australasian Plant Pathology Society Inc.

Individual-based modelling of the efficacy of fumigation tactics to control lesser grain borer (Rhyzopertha dominica) in stored grain

Increasing resistance to phosphine (PH 3) in insect pests, including lesser grain borer (Rhyzopertha dominica) has become a critical issue, and development of effective and sustainable strategies to manage resistance is crucial. In practice, the same grain store may be fumigated multiple times, but usually for the same exposure period and concentration. Simulating a single fumigation allows us to look more closely at the effects of this standard treatment.We used an individual-based, two-locus model to investigate three key questions about the use of phosphine fumigant in relation to the development of PH 3 resistance. First, which is more effective for insect control; long exposure time with a low concentration or short exposure period with a high concentration? Our results showed that extending exposure duration is a much more efficient control tactic than increasing the phosphine concentration. Second, how long should the fumigation period be extended to deal with higher frequencies of resistant insects in the grain? Our results indicated that if the original frequency of resistant insects is increased n times, then the fumigation needs to be extended, at most, n days to achieve the same level of insect control. The third question is how does the presence of varying numbers of insects inside grain storages impact the effectiveness of phosphine fumigation? We found that, for a given fumigation, as the initial population number was increased, the final survival of resistant insects increased proportionally. To control initial populations of insects that were n times larger, it was necessary to increase the fumigation time by about n days. Our results indicate that, in a 2-gene mediated resistance where dilution of resistance gene frequencies through immigration of susceptibles has greater effect, extending fumigation times to reduce survival of homozygous resistant insects will have a significant impact on delaying the development of resistance. © 2012 Elsevier Ltd.

Constructing a new individual-based model of phosphine resistance in lesser grain borer (Rhyzopertha dominica): do we need to include two loci rather than one?

In this article, we describe and compare two individual-based models constructed to investigate how genetic factors influence the development of phosphine resistance in lesser grain borer (R. dominica). One model is based on the simplifying assumption that resistance is conferred by alleles at a single locus, while the other is based on the more realistic assumption that resistance is conferred by alleles at two separate loci. We simulated the population dynamic of R. dominica in the absence of phosphine fumigation, and under high and low dose phosphine treatments, and found important differences between the predictions of the two models in all three cases. In the absence of fumigation, starting from the same initial frequencies of genotypes, the two models tended to different stable frequencies, although both reached Hardy-Weinberg equilibrium. The one-locus model exaggerated the equilibrium proportion of strongly resistant beetles by 3.6 times, compared to the aggregated predictions of the two-locus model. Under a low dose treatment the one-locus model overestimated the proportion of strongly resistant individuals within the population and underestimated the total population numbers compared to the two-locus model. These results show the importance of basing resistance evolution models on realistic genetics and that using oversimplified one-locus models to develop pest control strategies runs the risk of not correctly identifying tactics to minimise the incidence of pest infestation.

Red mahogany (plantations)

Red mahogany produces a hard, durable and attractive timber. In the past, small quantities of timber harvested from native forest has been used in construction, engineering and for appearance products and round timbers. It has well-established national markets, particularly in Queensland and NSW. It is also known in the international market as it is grown in plantations in other tropical regions.

Alginate encapsulation of shoot tips and nodal segments for short-term storage and distribution of the eucalypt Corymbia torelliana × C. citriodora

A protocol was developed for short-term preservation and distribution of the plantation eucalypt, Corymbia torelliana × C. citriodora, using alginate-encapsulated shoot tips and nodes as synthetic seeds. Effects of sowing medium, auxin concentration, storage temperature and planting substrate on shoot regrowth or conversion into plantlets were assessed for four different clones. High frequencies of shoot regrowth (76–100%) from encapsulated explants were consistently obtained in hormone-free half- and full-strength Murashige and Skoog (MS) sowing media. Conversion into plantlets from synthetic seeds was achieved on half-strength MS medium by treating shoot tips or nodes with 4.9–78.4 μM IBA prior to encapsulation. Pre-treatment with 19.6 μM IBA provided 62–100% conversion, and 95–100% of plantlets survived after acclimatisation under nursery conditions. Synthetic seeds containing explants pre-treated with IBA were stored for 8 weeks much more effectively at 25°C than at 4°C, with regrowth frequencies of 50–84% at 25°C compared with 0–4% at 4°C. To eliminate the in vitro culture step after encapsulation, synthetic seeds were allowed to pre-convert before sowing directly onto a range of ex vitro non-sterile planting substrates. Highest frequencies (46–90%) of plantlet formation from pre-converted synthetic seeds were obtained by transferring shoot tip-derived synthetic seeds onto an organic compost substrate. These plantlets exhibited almost 100% survival in the nursery without mist irrigation. Pre-conversion of non-embryonic synthetic seeds is a novel technique that provides a convenient alternative to somatic embryo-derived artificial seeds.

Corymbia phloem phenolics, tannins and terpenoids: interactions with a cerambycid borer

Plant secondary chemistry mediates the ability of herbivores to locate, accept and survive on potential host plants. We examined the relationship between attack by the cerambycid beetle Phoracantha solida and the chemistry of the secondary phloem (inner bark) of two differentially attacked plantation forestry taxa, Corymbia variegata and its hybrid with C. torelliana. We hypothesised that this differential rate of attack may have to do with differences in secondary chemistry between the taxa. We found differences in the bark chemistry of the taxa, both with respect to phenolic compounds and terpenoids. We could detect no difference between bored and non-bored C. variegata trees (the less preferred, but co-evolved host). Hybrid trees were not different in levels of total polyphenols, flavanols or terpenes according to attack status, but acetone extracts were significantly different between bored and non-bored trees. We propose that variations in the bark chemistry explain the differential attack rate between C. variegata and the hybrid hosts.