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OBJECTIVES To compare the mechanical properties of monofilament nylon leader and orthopaedic wire for median sternotomy closure in the dog. MATERIALS AND METHODS Median sternotomy was performed in 14 canine cadaver sternums with the manubrium intact. The sternotomy was closed with either 80 lb monofilament nylon leader or 20G orthopaedic stainless steel wire in a peristernal figure of 8 pattern. Constructs were loaded in a servohydraulic material testing machine. Load at yield, maximum load, stiffness, displacement and mode of failure were compared between constructs subjected to a single cycle load to failure. RESULTS No significant differences were found in load at yield, maximum load, stiffness or displacement between the monofilament nylon leader and the stainless steel wire constructs. No implant failure was evident in the stainless steel wire constructs. Four of the monofilament nylon leader constructs failed by pulling of the nylon through the crimp. CLINICAL SIGNIFICANCE Monofilament nylon leader is mechanically comparable to stainless steel wire and potentially a suitable alternative for closure of median sternotomy in the dog.

Tree growth and vegetative propagation are complex but important traits under selection in many tree improvement programmes. To understand the genetic control of these traits, we conducted a quantitative trait locus (QTL) study in three full-sib families of Eucalyptus nitens growing at two different sites. One family growing at Ridgley, Tasmania had 300 progeny and two clonally replicated families growing at Mt. Gambier, South Australia had 327 and 210 progeny. Tree growth was measured over several years at both sites and percentages of roots produced by either stem cuttings or tissue culture were assessed in the two Mt. Gambier families. Linkage analysis of growth traits revealed several QTLs for later year traits but few for early year traits, reflecting temporal differences in the heritabilities of these traits. Two growth QTL positions, one on LG8 and another on LG11 were common between the Ridgley and Mt. Gambier families. Four QTLs were observed for each of the two vegetative propagation methods. Two QTLs for vegetative propagation on LG7 and LG11 were validated in the second family at Mt. Gambier. These results suggest that growth and vegetative propagation traits are controlled by several small effect loci. The QTLs identified in this study are useful starting points for identifying candidate genes using the Eucalyptus grandis genome sequence.

We used association studies to identify allelic variation in genes that influence wood fibre development in Eucalyptus nitens (Deane and Maiden). Genes selected for analysis were differentially expressed in wood with contrasting properties such as cellulose and lignin content, pulp yield and microfibril angle (MFA). Single nucleotide polymorphisms (SNPs) were identified by sequencing the candidate genes in a number of unrelated individuals. Selected SNPs were genotyped across 420 unrelated E. nitens trees from central Victorian populations and growing in a provenance trial at Meunna in north-western Tasmania. Significantly associated SNPs were genotyped across two other populations in northern Tasmania in order to validate associated SNPs. We have compiled a database of phenotypic information relating particularly to wood fibre properties for each individual in the association and validation populations. Associations between SNPs and wood properties were identified by comparing trait means in different SNP genotype classes. Several significantly associated SNPs identified in the Meunna population were validated in the other populations. The direction of the allele effect was reversed for two SNPs that were associated with kraft pulp yield. DNA markers identified in this research may be used to complement existing selection methods in breeding programs.

Most conifer species occur in large continuous populations, but radiata pine, Pinus radiata, occurs only in five disjunctive natural populations in California and Mexico. The Mexican island populations were presumably colonized from the mainland millions of years ago. According to Axelrod (1981), the mainland populations are relicts of an earlier much wider distribution, reduced some 8,000 years ago, whereas according to Millar (1997, 2000), the patchy metapopulation-like structure is typical of the long-term population demography of the species. We used 19 highly polymorphic microsatellite loci to describe population structure and to search for signs of the dynamics of population demography over space and time. Frequencies of null alleles at microsatellite loci were estimated using an approach based on the probability of identity by descent. Microsatellite genetic diversities were high in all populations [expected heterozygosity (H(e)) = 0.68-0.77], but the island populations had significantly lower estimates. Variation between loci in genetic differentiation (F(ST)) was high, but no locus deviated statistically significantly from the rest at an experiment wide level of 0.05. Thus, all loci were included in subsequent analysis. The average differentiation was measured as F(ST) = 0.14 (SD 0.012), comparable with earlier allozyme results. The island populations were more diverged from the other populations and from an inferred common ancestral gene pool than the mainland ones. All populations showed a deficiency of expected heterozygosity given the number of alleles, the mainland populations more so than the island ones. The results thus do not support a recent important contraction in the mainland range of radiata pine.

Ten microsatellite loci were used to DNA profile 215 first and second generation breeding clones in the Australian radiata pine breeding program. The clones were essentially unique from one another and these DNA profiles were used to examine the sexual and asexual phases in the breeding program. Only 2.6% of ramets from 25 breeding clones were incorrect whereas 8.4% of progeny from 10 families were genetically incorrect. The lineages of second generation clones were checked for DNA profiles that were available for putative parents. Some parents appear to be incorrect on the basis of the DNA profiles and further sampling will be required to confirm these results across the breeding program. Microsatellite markers can now enable most questions to be resolved in breeding programs and also will allow novel breeding strategies to be used in the future.

There are several practically important engineering systems that fail by scuffing long after the initial running-in has been completed. A common feature of these systems is repeated contact between the same points on the mating surfaces. The processes leading up to such mid-life scuffing failures have been examined by monitoring the development of cam follower surface roughness and wear at regular intervals during a series of valve train wear tests in a fired engine. By the application of both statistical and numerical models for the elastic contact of rough surfaces, the following stages in the scuffing process have been identified: (a) surface roughening in the mild-wear regime, which progressively increased maximum asperity contact pressures until (b) the elastic shakedown limit was exceeded, causing plastic deformation wear, accelerated roughening and enlargement of valleys, leading eventually to (c) a transition to high rates of wear, probably resulting from hydrodynamic pressure loss and oil-film collapse.

The ability of motor oils to control valve train wear adequately is ensured by the evaluation of new formulations in a variety of standard industry tests. The most critical of these tests have single-overhead-cam valve train systems with pivoted (rocker- or finger-type) followers. Although many vehicles in service have these types of valve train, there is a strong trend towards the use of roller-follower and direct-acting tappet (DAT) systems in recently introduced passenger car engine designs. Roller designs virtually eliminate sliding between the cam and follower and in gasoline engines reduce wear and friction to low levels. Practical experience indicates that DAT systems also give lower wear and friction than pivoted systems do. The parameters affecting wear in the pivoted-follower valve trains of the Sequence VE and Peugeot TU-3 tests are analysed in comparison with equivalent DAT systems. The friction and wear benefits observed with DAT systems are shown to be inherent in the geometry and kinematics of this type of valve train. The consequences of this finding are discussed in relation to the requirements for antiwear protection provided by future motor oils.

Analysis of used oils from a series of Peugeot TU-3 engine tests has been performed to investigate the effect of engine operating temperature on valve train wear in this engine. Iron content of intermediate and end-of-test used oil samples has been used as a monitor of valve train wear during the test and has indicated that a significant proportion of the wear occurs during the initial low-temperature phase of the test. Analysis of used oils using 31phosphorus nuclear magnetic resonance spectroscopy (3lP NMR) suggests that this is associated with low rates of zinc dialkyldithiophosphate (ZDTP) degradation during low-temperature operation, resulting in levels of extreme-pressure (e.p.)/anti-wear materials which are insufficient to provide the necessary wear protection. Modification of the TU-3 test procedure, such that the high operating temperature phase precedes the low-temperature phase, results in very much lower observed levels of valve train wear.31 P NMR analysis indicates that this is associated with a much more rapid buildup of active ZDTP degradation products during initial high-temperature operation, which can then provide the necessary anti-wear protection during subsequent low-temperature operation.

The positions of maximum wear on the surfaces of automotive cams and followers have been found to be characterized by low velocities of the point of contact over the surface in question, in combination with significant sliding velocities and thin oil films. The modelling of these critical conditions has now been extended to examine the significance of low contact velocities in two internationally accepted engine tests for the evaluation of the anti-wear properties of lubricants in valve train systems. Calculations of the contact dwell times and the corresponding sliding distances against the opposing surfaces indicate that the particular susceptibility to wear and surface distress in these systems arises from the extreme values of these parameters experienced by particular points on the surfaces during each rotation of the cam. The conditions on the follower surfaces appear to be more severe than on the cams in this respect. It is shown that kinematic conditions representative of the more severe parts of the operating cycles of the engine tests can be reproduced in a modified Amsler two-disc machine, thus enabling the use of small, flat test specimens, which are accessible to a wide range of advanced surface analysis instruments, to facilitate the study of lubricant anti-wear additive film formation.

A genetic linkage map for radiata pine (Pinus radiata D. Don) has been constructed using segregation data from a three-generation outbred pedigree. A total of 208 loci were analyzed including 165 restriction fragment length polymorphism (RFLP), 41 random amplified polymorphic DNA (RAPD) and 2 microsatellite markers. The markers were assembled into 22 linkage groups of 2 or more loci and covered a total distance of 1382 cM. Thirteen loci were unlinked to any other marker. Of the RFLP loci that were mapped, 93 were detected by loblolly pine (P. taeda L.) cDNA probes that had been previously mapped or evaluated in that species. The remaining 72 RFLP loci were detected by radiata pine probes from a PstI genomic DNA library. Two hundred and eighty RAPD primers were evaluated, and 41 loci which were segregating in a 1∶1 ratio were mapped. Two microsatellite markers were also placed on the map. This map and the markers derived from it will have wide applicability to genetic studies in P. radiata and other pine species.

We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of T(RAD)=300 eV and a symmetric implosion to a 100 μm diameter hot core.

Experimental studies have been carried out with two different coupled electrochemical oscillators. The First study was described in the preceding article. In this present paper we consider cobalt electrodes in hydrochloric acid chromic acid electrolytes, Two electrodes, one of which was embedded in a rotating disk and the other of which was in a nonrotating disk parallel to the first, were used. Several types of phenomena due to coupling were observed. Each electrode can drive the other. Phase-locked oscillations were observed when neither, either, or both of the electrodes were held at a potential where oscillations occur independently

The 5S RNA genes inPinus radiata occur in two size classes of about 850 and 525 bp in length. Representatives from both the long and short size classes were cloned and sequenced. The primary difference in the two size classes was shown to be a 330 bp insertion in the spacer region of the long units. Within an individual breeding clone ofP. radiata there was some sequence heterogeneity between representatives of the short class. The 5S RNA genes in thirty pine species were characterised using either a clone of the short size class or a subclone of the 330 bp insertion characterizing the long size class. Eleven species of subg.Strobus were examined and all lacked the long type of unit of radiata pine. The New World species of subg.Pinus all had both short and long units whereas the Old World species had long units. The implications of these results for the evolution of the 5S DNA sequences and the phylogenetic relationships withinPinus are discussed.

Pollen of acacias is transported by insects as polyads, composite pollen grains. The polyad has enough pollen grains to fertilize all ovules within a flower and hence all seed within a pod may be full sibs. Isozyme markers were used to test this hypothesis in two populations of Acacia melanoxylon R.Br. The proportions of fruit pods with multiple paternity detected in two populations were 0.08 and 0.15. The proportions of fullsib pairs within pods estimated by the sibling pair method were 1 and 0.63 for the two populations. Comparison of the diploid paternal genotypes of pods of single paternity showed that the probability of a common pollen source for a pair of pods was high within globular clusters (0.35) or within inflorescences (0.46) but declined to 0.10 or 0.25 within the tree at random. Thus the reproductive system acted to reinforce a hierarchy of paternal correlation within each tree.

Patients with high-risk bladder cancer who do not respond to bacillus Calmette-Guerin (BCG) immunotherapy represent a significant therapeutic challenge. The addition of interferon to BCG has recently evolved as a second-line treatment option; however, many high-grade tumors are nonresponsive to interferon. Thus, replication-competent oncolytic vesicular stomatitis viruses (VSV) that selectively target interferon-refractory tumors are promising intravesical agents. In vitro, wild-type VSV as well as a mutant variant (AV3) that has an impaired ability to shut down innate immunity preferentially killed undifferentiated, interferon-nonresponsive bladder cancer cells. Testing of these viruses in an orthotopic murine model of high-grade bladder cancer, which we have recently validated, revealed that both AV3 and wild-type VSV significantly inhibited orthotopic tumor growth. Despite the use of immunocompromised nude mice, there was no evidence of toxicity. In conclusion, VSV instillation therapy demonstrated strong antitumor activity and safety in an orthotopic model of high-risk disease. These findings provide preclinical proof-of-principle for the intravesical use of VSV, especially in interferon-refractory patients.

Phylogenetic relationships among the 12 species of the “green ash” group of eucalypts were examined using allozyme data, to investigate the causes of rarity in three localized endemics of the group. The relationships suggested by the allozyme data showed both similarities to and differences from those estimated from morphological data byLadiges and coworkers. The phylogenetic relationships suggest that rarity inEucalyptus burgessiana may be related to recent divergence, whileE. paliformis andE. rupicola are relatively old species, more likely to be relicts, and/or restricted to a rare habitat.

SummaryThe purpose of this study was to compare the holding powers of 2.7 mm pre-tapped and self-tapped screws placed closely together and tightened in small bones. Pairs of metatarsals were collected from healthy, skeletally mature Greyhounds and part of a 2.7 mm dynamic compression plate was fixed to the dorsal surface of each bone using three 2.7 mm screws. Identical screws were used throughout but only one of each pair of bones had threads pre-cut using a tap prior to insertion. All of the screws were tightened before the constructs were mounted in a materials testing machine and the centrally placed screw was loaded incrementally until failure. Load-deformation curves were plotted and yield point, ultimate load to failure, stiffness and energy prior to yield point were measured. Mean values were recorded for each parameter and Student's T-test was used to test the null hypothesis that there is no difference in holding power between pre-tapped and self-tapped screws. Significant mechanical differences were not found between pre-tapped and self-tapped screws placed closely together and tightened into small bones. Self-tapped screws can be considered for use in small animal surgery even when multiple screws are to be placed closely together in relatively small pieces of bone.

Six related radiata pine ( Pinus radiata) full-sib families were used to detect and independently verify quantitative trait loci (QTLs) for resistance to Dothistroma needle blight, caused by Dothistroma septospora. The detection families had from 26 to 30 individuals each, and had either a common maternal (31053) or paternal (31032) parent; one family (cross 4) consisted of progeny from both parents, 31053 x 31032. Approximately 200 additional progeny from cross 4 were clonally replicated and planted at two sites, with at least five to seven ramets of each individual per site. Marker segregation data were collected from a total of 250 RFLP and microsatellite markers, and single factor ANOVAs were conducted separately for each family and marker. A number of putative associations were observed, some across more than one family. Permutation tests were used to confirm expected probabilities of multiple associations based on chance alone. Seven markers representing at least four QTLs for resistance to Dothistroma were identified as being significant in more than one family; one of these was significant at P0.05 in three families and highly significant at P0.01 in a fourth. Further confirmation was obtained by testing those markers that were significant in more than one of the detection families (or highly significant in cross 4) in the clonally replicated progeny from cross 4. Four QTL positions were verified in the clonal populations, with a total percent variation accounted for of 12.5.

Fifty microsatellite markers were developed and characterized in Pinus radiata, and from among these, a subset of 10 easily scored and highly polymorphic markers was selected for use in fingerprinting, quality control, and breeding applications. The markers were characterized based on reliable and reproducible amplification, observed and expected heterozygosities, number of alleles, a low frequency of null alleles, and a lack of close linkage with other selected markers. Allele numbers and frequencies were estimated using 24 first-generation breeding clones from Australia and New Zealand. Observed heterozygosities for the selected markers were all greater than 0.67, and there was an average of 10.5 alleles/locus. The occurrence of null alleles was checked with megagametophytes from mother trees for loci that appeared to be homozygous. The 10 markers are not closely linked (r < 0.20 and LOD > 3) to each other. The selected microsatellites fall into three discrete size classes, and with appropriate selection of fluorescent dyes for 5' end labeling, can be multiplexed with up to 6 markers/sample on an ABI PRISM 310 or similar instrument.Key words: pine microsatellites, multiplexing, null alleles.

The management of choledocholithiasis has changed radically since the introduction of laparoscopic cholecystectomy. However, perceived technical difficulties have deterred many surgeons from treating common bile duct stones laparoscopically at the time of cholecystectomy. This has lead to reliance on endoscopic retrograde cholangiopancreatography followed by endoscopic sphincterotomy to deal with common bile duct stones. We retrospectively reviewed the charts of patients who had laparoscopic common bile duct exploration at Downe Hospital between December 1999 and August 2001. Among 149 laparoscopic cholecystectomies done by our group in this period, 10 patients (6.7%) underwent laparoscopic CBD exploration, three by the transcystic technique and seven by choledochotomy. Three patients (2%) had unsuspected stones found on routine per- operative cholangiogram. The mean operative time was 2.34hrs (range 1.50-3.30hrs). The mean hospital post- operative stay was 3 days (range 1-6 days). Post-operative morbidity was zero. Stone clearance was achieved in all cases. We conclude, laparoscopic exploration of the common bile duct is relatively safe and straightforward method. The key skill required is the ability to perform laparoscopic suturing with confidence.

AIMSTo investigate the relation between haemoglobin in children followed longitudinally from 8 to 18 months, and developmental outcome at 18 months.METHODSThe Avon Longitudinal Study of Pregnancy and Childhood (ALSPAC) is a longitudinal survey of a geographically defined population of children born in 1991–92. In a randomly selected subsample, blood samples were assayed for Hb at 8, 12, and 18 months; a developmental assessment was carried out at 18 months on 1141 children using the Griffiths Scales of Mental Development.RESULTSThere was a strong quadratic association between Hb at 8 months and performance on the locomotor subscale at 18 months. Average scores increased with increasing Hb up to 95 g/l; there was little additional developmental benefit in Hb levels beyond 95 g/l. Infants with Hb CONCLUSIONSLow Hb concentrations (⩽ 95 g/l) in 8 month old children are associated with impaired motor development at 18 months. This cut off point corresponds to the 5th centile of Hb at 8 months. The results indicate that if there is an adverse effect of low Hb on developmental outcome, screening may be more effective at 8 months or earlier, rather than after this age. We propose to examine the importance of infant anaemia in relation to more accurate and detailed long term outcomes as the children get older.

The eukaryotic genome codes for most of its proteins though discontinuous coding sequences called exons, which are separated by noncoding sequences known as introns. Following transcription of a gene, these exons must be spliced precisely, removing the intervening introns, to form meaningful mature messenger RNAs (mRNA) that are transported to the cytoplasm and translated by the ribosomal machinery. To add yet another level of complexity, a process known as alternative splicing exists, whereby a single pre-mRNA can give rise to two or more mature mRNAs depending on the combination of exons spliced together. Alternative splicing of pre-mRNAs is emerging as an important mechanism for gene regulation in many organisms. The classic example of splicing as a regulator of genetic information during a developmental process is sex determination in Drosophila. The now well-characterized cascade of sex-specific alternative splicing events demonstrates nicely how the control of splice site selection during pre-mRNA processing can have a profound effect on the development of an organism. The factors involved in pre-mRNA splicing and alternative splice site selection have been the subject of active study in recent years. Emerging from these studies is a picture of regulation based on protein-protein, protein-RNA, and RNA-RNA interactions. How the interaction of the various splicing constituents is controlled, however, is still poorly understood. One of the mechanisms of regulation that has received attention recently is that of posttranslational phosphorylation. In the following article, we cite the evidence for a role of phosphorylation in constitutive and alternative splicing and discuss some of the recent information on the biochemistry and biology of the enzymes involved.

The role of the nucleus in protein synthesis reprogramming during oocyte maturation was examined in immature or mature bovine oocytes, enucleated at the germinal vesicle (GV) stage or the metaphase II (MII) stage. Cumulusoocyte complexes (COCs) were denuded before or after maturationin vitro. Denuded oocytes were (i) enucleated at the GV or MII stage (after DNA staining and ultraviolet (UV) exposure), (ii) stained and exposed to UV but not enucleated, or (iii) used as controls. After treatment, oocytes were labelled for 4 h with35S-methionine or were matured for 24 h before labelling. GV- or MII- karyoplasts and small portions of cytoplasm (cytoplasts), removed during enucleation, were also labelled. Labelled oocytes, karyoplasts or cytoplasts were prepared for one-dimensional polyacrylamide gel electrophoresis. Incorporation of labelled methionine into oocyte protein was measured. Enucleation did not affect protein synthesis reprogramming, but incorporation of 35S-methionine in immature UV-stained oocytes was high-possibly due to nuclear repair mechanisms. Protein proles of GV- and MII- karyoplasts differed from those of immature and mature oocytes. In conclusion, normal protein synthesis reprogramming in the cytoplasm can occur in the absence of the nucleus, and specic proteins are synthesized in the nuclear region.

Myelin-associated glycoprotein (MAG) is a myelin-specific cell adhesion molecule of the immunoglobulin supergene family and is tyrosine-phosphorylated in the developing brain. To define the role of MAG in signal transduction, the tyrosine phosphorylation sites were analyzed. The major tyrosine phosphorylation residue was identified as Tyr-620, which was found to interact specifically with the SH2 domains of phospholipase C (PLC gamma). This domain may represent a novel protein binding motif that can be regulated by tyrosine phosphorylation. MAG also specifically bound the Fyn tyrosine kinase, suggesting that MAG serves as a docking protein that allows the interaction between different signaling molecules.

Pressure ulcer prevention and treatment are major issues in health care, with new products flooding the market constantly. This article presents the results of a clinical investigation of four pressure-reducing mattresses and a foam overlay used in five different nursing units (neurology, oncology, respiratory, medical/surgical intensive care, and cardiovascular surgery). A total of 246 patients were evaluated on the trial mattresses and 46 were evaluated on the foam overlay.

We have isolated cDNAs encoding kinases from a murine pre-B cell line by screening a lambda gt11 cDNA expression library with anti-phosphotyrosine antibodies. One cDNA was identified to encode the previously isolated tyrosine kinase c-lyn. Among the remaining clones, we have characterized a cDNA encoding a novel kinase which we have designated TIK. Sequence analysis of this cDNA indicates that the TIK enzyme lacks the features thought to be conserved among protein tyrosine kinases. Although isolated on the basis of its reactivity with the anti-phosphotyrosine antibody, the TIK enzyme was found to have only serine and threonine kinase activity. The amino-terminal portion of the TIK protein contains a cdc2 phosphorylation consensus sequence. Three mRNA transcripts derived from the TIK gene are detected in a variety of adult murine tissues.

Eucalyptus cladocalyx F.Muell. is a widely cultivated tree in dryland southern Australia. It is grown for firewood, timber production and as a windbreak and ornamental species. Natural populations of E. cladocalyx are endemic to South Australia where they occur in three disjunct regions. This study assessed the mating system and patterns of genetic diversity in natural populations of E. cladocalyx by using allozymes. Populations had relatively low levels of genetic diversity (HE = 0.148) and high levels of genetic divergence (θ = 0.26) among populations, similar to other regionally distributed eucalypts. Populations clustered into three distinct groups, which corresponded to its disjunct natural distribution. Genetic differentiation among populations and between regions was highly significant. Relatively high levels of inbreeding (tm = 0.57) were detected in natural populations of E.�cladocalyx. Outcrossing rates were highly variable among families, ranging from 0 to 100%. One-third of families from four populations had outcrossing rates that were not significantly different from zero. The origins of three commercially significant, cultivated stands of E. cladocalyx were also assessed. Allozyme profiles of cultivated stands from Wail and Lismore in western Victoria suggested origins in the Wirrabara region of the southern Flinders Ranges, while a cultivated stand of E. cladocalyx var. nana Hort. ex Yates had an allozyme profile consistent with origins in the Eyre Peninsula region. The results are discussed in relation to the species' morphological variation, biogeography and the implications for its domestication and conservation.

The distribution of genetic variation within and among species inCorymbia section‘Politaria’ was examined using allozymes.This section consists of four species,Corymbia citriodora (Hook.) K.D.Hill & L.A.S.Johnson, C. maculata (Hook.) K.D.Hill & L.A.S.Johnson, C. henryi (Blake) K.D.Hill & L.A.S.Johnson and C. variegata (F.Muell.) K.D.Hill & L.A.S.Johnson, which are of commercial interest for plantation and farmforestry. Thirty populations representing the species’ range-widedistributions were studied, extending from upland tropical regions of northQueensland, south to eastern Victoria. Despite relatively low allozymedivergence between species, there was a relationship between geographicdistribution patterns of populations and allozyme variation. The section wasshown to comprise very closely related species with only 15% of thetotal genetic diversity attributed to differences between species. Twodistinct genetic alliances were evident:C. maculata–C. henryi andC. citriodora–C. variegata.Corymbia citriodora andC. variegata, however, could not be distinguished bytheir allozyme profiles. The lack of genetic differentiation between thesetaxa suggests that they represent one species composed of two chemical races.Corymbia maculata and C. henryiwere shown to be closely allied but genetically distinct.Corymbia henryi had the highest genetic diversity in thegroup and lowest differentiation among populations, whileC. maculata had the lowest diversity but the highestgenetic differentiation among populations. There was evidence ofisolation-by-distance among populations ofC. citriodora, C. maculata andC. variegata but not in C. henryi,which has a smaller geographic range. The inclusion in the study ofC. torelliana (F.Muell.) K.D.Hill & L.A.S.Johnson asan outgroup accentuated the small genetic differences between species in thegroup. The patterns of genetic diversity are discussed in relation to thespecies’ taxonomic relationships, breeding systems and utilisation.

Acacia tumida F.Muell ex. Benth. is a morphologically variable species from north-western Australia. Variants range from low, multi-stemmed shrubs to single-stemmed trees. Acacia tumida is cultivated for firewood, windbreaks and sand stabilisation. To examine patterns of genetic variation that could be utilised in domestication programs, 22 populations representing its natural distribution were surveyed by using allozymes. Estimates of genetic diversity (HE = 0.149) were within the range of other tropical, widespread woody plants, but varied widely among populations (HE = 0.064–0.203). There were strong clinal trends in diversity estimates; A, P, HO, HE were correlated with longitude and declined from west to east. HE decreased as mean monthly maximum temperatures increased and allelic richness (A) increased with mean minimum monthly temperatures. There were also significant correlations between allele frequencies at certain loci and geographic and climatic parameters. Significant isolation-by-distance and relatively high levels of differentiation (θ = 0.176) were detected among populations. Populations of the narrow-phylloded form (Pilbara region) were the most genetically divergent, despite their geographic proximity to other populations. The low-shrub and tall-tree forms could not be distinguished by allozyme profiles. Slight genetic differences were detected between the non-pruinose and pruinose forms from within one population. Phylogenetic analysis supported morphological evidence of hybridisation between A. tumida and A. difficilis Maiden in their zone of overlap. The results are discussed in relation to the taxonomy and domestication of A. tumida.

The distribution of genetic variation within and among species inCorymbia section‘Politaria’ was examined using allozymes.This section consists of four species,Corymbia citriodora (Hook.) K.D.Hill & L.A.S.Johnson, C. maculata (Hook.) K.D.Hill & L.A.S.Johnson, C. henryi (Blake) K.D.Hill & L.A.S.Johnson and C. variegata (F.Muell.) K.D.Hill & L.A.S.Johnson, which are of commercial interest for plantation and farmforestry. Thirty populations representing the species’ range-widedistributions were studied, extending from upland tropical regions of northQueensland, south to eastern Victoria. Despite relatively low allozymedivergence between species, there was a relationship between geographicdistribution patterns of populations and allozyme variation. The section wasshown to comprise very closely related species with only 15% of thetotal genetic diversity attributed to differences between species. Twodistinct genetic alliances were evident:C. maculata–C. henryi andC. citriodora–C. variegata.Corymbia citriodora andC. variegata, however, could not be distinguished bytheir allozyme profiles. The lack of genetic differentiation between thesetaxa suggests that they represent one species composed of two chemical races.Corymbia maculata and C. henryiwere shown to be closely allied but genetically distinct.Corymbia henryi had the highest genetic diversity in thegroup and lowest differentiation among populations, whileC. maculata had the lowest diversity but the highestgenetic differentiation among populations. There was evidence ofisolation-by-distance among populations ofC. citriodora, C. maculata andC. variegata but not in C. henryi,which has a smaller geographic range. The inclusion in the study ofC. torelliana (F.Muell.) K.D.Hill & L.A.S.Johnson asan outgroup accentuated the small genetic differences between species in thegroup. The patterns of genetic diversity are discussed in relation to thespecies’ taxonomic relationships, breeding systems and utilisation.

Twenty-three isozyme loci were used to examine genetic diversity within and between 19 natural populations of Acacia mearnsii De Wild. selected to represent its entire geographic range. Acacia mearnsii was found to have moderate genetic diversity (species level gene diversity HT = 0.201) with the majority (89.2%) of variation occurring within populations. All measures of population diversity were higher in the northern (New South Wales) than the southern (Victoria, South Australia, Tasmania) populations. There was some evidence of differentiation between populations but no strong clustering at a regional level.

Genetic variation in 23 natural populations of Grevillea robusta A.Cunn. from across the natural range of the species was examined using 20 isozyme loci assayed in young seedlings. Mean expected heterozygosity per population, He , varied from 0.080 to 0.131 with an average of 0.105. The genetic diversity of individual populations did not appear to be related to their ecological characteristics (araucarian vine forest or riverine habitat types) or their geographic locations. A genetic distance analysis indicated a significant separation of the populations into two regional groups, eight from the northern part of the natural range and the remaining 15 from central and southern areas. Between-population differences accounted for 17.9% of the total genetic variation, one-third of which was attributable to the difference between the two regional groups. Most alleles at the 20 loci occurred across most or all of the geographic range. This, and the low level of genetic differentiation between populations, suggest that genetic exchange between populations has been maintained, despite the pattern of natural distribution of the species in small, separated populations.

Isozyme variation in two closely related red mahoganies (Eucalyptus pellita F. Muell. and E. scias L.A.S.Johnson and K.D.Hill) was examined in 17 populations of E. pellita from Australia, Papua New Guinea and Indonesia and 8 of E. scias (including all 3 subspecies) from south-eastern coastal Australia. Measures of genetic diversity and relationships between species and subspecies were based on 15 variable loci. Both E. pellita and E. scias had moderately high levels of genetic diversity, comparable to other similarly distributed species. Most genetic diversity within each species was found within populations (80% in E. pellita and 83% in E. scias). There were substantial allelic differences between the species at several loci; the populations clustered into groups corresponding to the two species. Yet genetic differentiation between the two species was relatively low, and the three subspecies of E. scias were not well separated. Outcrossing rates in E. pellita are variable, with low rates (

A study of allozyme variation in Acacia melanoxylon R. Br. in 27 populations from across the geographic range of the species indicated high genetic diversity compared to other Australian trees and plants generally. Clines of increasing genetic variability with increasing latitude were found for four measures of genetic diversity. Most of the genetic diversity is found within populations but there was an unusually high level of the variation between populations (37.7%). A distinct genetic separation between the northern and southern populations was located approximately at the Hunter River region, where there is also a disjunction in the distribution of the species. The Nei (1978) genetic distance between these populations within this species is larger than observed between some plant species. Clearly the species has evolved separately in the two regions for a considerable time.

Polymorphisme de 30 loci etudie chez 11 populations d'Acacia mangium du Nord de l'Australie et de la Papouasie et comparaison avec la diversite genetique d'autres especes d'acacia