Variation amongEucalyptus species in resistance to eucalyptus longhorned borer in Southern California

Eucalyptus L'Héritier (Myrtaceae: Leptospermoideae) species are native to the Austro-Malaysian region, but have been widely planted in temperate and subtropical regions around the world. In most regions whereEucalyptus have been imported, the Eucalyptus Longhorned Borer (Phoracantha semipunctata F.) (Coleoptera: Cerambycidae) has been accidently introduced. Larvae of the beetle bore through the bark and mine along the cambium of stressed trees, usually killing their host. We report here the relative susceptibilities of 12Eucalyptus species in two mixed-species plantations in California, USA. These trees were stressed by water deficit resulting from a prolonged drought.Eucalyptus species that appeared resistant to the borer includedE. camaldulensis Dehnhardt,E. cladocalyx F. Muller,e. sideroxylon A. Cunn. ex Woolls, andE. trabutii (anE. camaldulensis hybrid). Species that were more susceptible to attack wereE. diversicolor F. Mueller,E. globulus LaBillardière,E. grandis Hill ex Maiden,E. nitens (Deane & Maiden),E. saligna Sm., andE. viminalis LaBillardière. Survival of trees was influenced by fine-scale moisture variation resulting from slope and irrigation effects. Resistance characteristics of theseEucalyptus species did not correlate with taxonomic relatedness or bark characteristics, but did correspond to drought tolerance traits in their native habitat.Eucalyptus species that were resistant to attack byP. semipunctata were those that are most tolerant of drought in Australia.     

Sensitivity of Aedes aegypti adults (Diptera: Culicidae) to the vapors of Eucalyptus essential oils

Vapors of essential oils extracted from various species of Eucalyptus (E. gunnii, E. tereticornis, E. grandis, E. camaldulensis, E. dunnii, E. cinerea, E. saligna, E. sideroxylon, E. globulus ssp. globulus, E. globulus ssp. maidenii, E. viminalis and the hybrids E. grandis × E. tereticornis and E. grandis × E. camaldulensis) and their major components were found to be toxic to Aedes aegypti adults, the yellow fever mosquito.An aliquot of each oil was placed in a cylindrical test chamber and the number of knocked-down mosquitoes was recorded as function of time. Knockdown time 50% was then calculated. Results showed that E. viminalis had the fastest knockdown time at of 4.2 min, on the same order as dichlorvos, a standard knockdown agent. A correlation was observed between the content of 1,8-cineole in the Eucalyptus essential oils and the corresponding toxic effect.The correlation between KT₅₀ values and calculated vapor pressures of the essential oil components showed that the fumigant activity of simple organic compounds in insects is correlated with their volatility.     

Comparative genetic linkage maps of <Emphasis Type="Italic">Eucalyptus grandis</Emphasis>, <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> and their F<Subscript>1</Subscript> hybrid based on a double pseudo-backcross mapping approach

Comparative genetic mapping in interspecific pedigrees presents a powerful approach to study genetic differentiation, genome evolution and reproductive isolation in diverging species. We used this approach for genetic analysis of an F₁ hybrid of two Eucalyptus tree species, Eucalyptus grandis (W. Hill ex Maiden.) and Eucalyptus globulus (Labill.). This wide interspecific cross is characterized by hybrid inviability and hybrid abnormality. Approximately 20% of loci in the genome of the F₁ hybrid are expected to be hemizygous due to a difference in genome size between E. grandis (640 Mbp) and E. globulus (530 Mbp). We investigated the extent of colinearity between the two genomes and the distribution of hemizygous loci in the F₁ hybrid using high-throughput, semi-automated AFLP marker analysis. Two pseudo-backcross families (backcrosses of an F₁ individual to non-parental individuals of the parental species) were each genotyped with more than 800 AFLP markers. This allowed construction of de novo comparative genetic linkage maps of the F₁ hybrid and the two backcross parents. All shared AFLP marker loci in the three single-tree parental maps were found to be colinear and little evidence was found for gross chromosomal rearrangements. Our results suggest that hemizygous AFLP loci are dispersed throughout the E. grandis chromosomes of the F₁ hybrid.Communicated by O. Savolainen     

Pollen dispersal from exotic eucalypt plantations

The introgression of genes from exotic species or populations into gene pools of native species is a widespread concern in agricultural systems. This is also an issue of increasing importance in forest systems as there has been a dramatic expansion of tree plantations, which have now reached 180 million ha globally. This has recently occurred in Australia with eucalypts. To help assess the risk of genetic pollution, we assess the pattern of realised pollen dispersal from exotic Eucalyptus nitens plantations into native E. ovata forest in Tasmania. We assessed the frequency of F₁ hybrids in open-pollinated seed collected from native E. ovata trees located at varying distance from three exotic E. nitens plantations in Tasmania. Over 119,000 seedlings were screened for morphological markers diagnostic of each species and the F₁ hybrid. F₁ hybridisation averaged 7.2% within 100 m of the exotic E. nitens, with one native tree reaching 56%, but diminished to 0.7% by 200–300 m and continued at this low level to the limits of the sampling at 1.6 km. The decay in the percentage of interspecific F₁ hybridisation with distance followed a power function with a negative exponent (%F₁ = 91.435distance^–0.789; R²=0.84). Eucalyptus nitens is exclusively pollinated by small insects (smaller than honeybees), which the study shows can disperse pollen over 1.6 km. However, the restriction of most exotic F₁ hybridisation to within 200 m of exotic plantations presents clear opportunities to manage the genetic impacts of plantations on native forests.     

Photosynthetic responses to overnight frost in Eucalyptus nitens and E. globulus

Significant expansion in the area of eucalypt plantations in Tasmania has led to their establishment at altitudes that are close to the upper limits of the planting distributions of Eucalyptus nitens and E. globulus, the main species planted. This has implications for plantation productivity. We investigated the processes that limit productivity in these environments through a study of freezing-induced depression of photosynthesis of E. nitens saplings in the field and plantlets of E. nitens and E. globulus clones in a controlled environment cabinet. In the field consecutive frosts of around –4.6°C had a cumulative effect, reducing maximum net photosynthesis ( A _max) by 17%, and then a further 9%, respectively, compared with saplings insulated from the frosts. Shading saplings pre-dawn had no effect on A _max measured after 1030 hours indicating that the reduction in A _max at this time was independent of photoinhibition. Recovery of A _max to pre-frost levels required at least two consecutive frost-free nights and was dependent on the severity of frost. Photosynthetic light response curves indicated that reduced A _max was associated also with decreased quantum yield and stomatal conductance. Similar intracellular carbon dioxide concentration between exposed and insulated saplings indicated that low stomatal conductance did not limit photosynthesis through carbon dioxide limitation. The timing of frost events was critical: E. nitens saplings took less time to recover from reduced A _max in the field when they were hardened. Unhardened plantlets of E. nitens and E. globulus clones had greater reduction of A _max and took longer to recover from frost events than hardened plantlets. E. globulus was more susceptible to frost-induced reduction of A _max than E. nitens. This is consistent with its planting range which is restricted to mild sites compared with that of E. nitens.     

Root-promoting rhizobacteria in <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> cuttings

Cloned Eucalyptus spp. plantations are based in greenhouse production of plants generated by vegetative propagation. Diverse studies have demonstrated that rhizospheric bacteria can stimulate plant growth, and more recently that they can increase rooting in vegetative material. Considering this potential, the objective of this study was to verify the effect of bacterial strains on rooting Eucalyptus globulus. A total of 132 bacterial strains isolated from the rhizosphere of E. globulus and Eucalyptus nitens were studied. The bacterial inoculums in a concentration of 4 × 10⁸ cfu/ml were applied to the rooting substrate at the cutting installation and 45 days after by irrigation. Rooting was evaluated on days 60 and 75 after cutting installation, considering the number of roots as well as their fibrosity and roots biomass. Of the 132 strains evaluated, 26 significantly increased cutting rooting in a range of 191.4–69.4% with respect to the control. Additionally, some strains stimulated the development of fine roots and incremented the roots biomass. The strains identificated that produced a rooting effect were: Bacillus firmus, Bacillus mycoides, Bacillus stearothermophilus, Bacillus subtilis, B. subtilis/amyloliquefaciens, Bacillus circulans, Brevibacillus brevis, Paenibacillus lautus and Stenotrophomona maltophilia. These first trials suggest the potential of these bacteria to be used in clonal production programs for E. globulus.     

A comparison of genetic information from open-pollinated and control-pollinated progeny tests in two eucalypt species

Genetic-parameter estimates and parental breeding-value predictions were compared from open-pollinated and control-pollinated progeny populations of Eucalyptus globulus and two populations of E. nitens. For E. globulus there were two types of open-pollinated populations (native stand open-pollinated and seed orchard open-pollinated) and two types of control-pollinated populations (intra-provenance and interprovenance full-sib families). For E. nitens there were two populations, a seed orchard open-pollinated population and intra-provenance full-sib families. Progeny tests were established across multiple sites and 2-year height and diameter were measured and volume calculated. Genetic parameters from native stand open-pollinated E. globulus were unlike the parameters from the other three E. globulus populations; heritability estimates were severely inflated, presumably due to high levels, and possibly differential levels, of inbreeding depression relative to the other populations. Estimates of dominance variance in the E. globulus full-sib populations were high, but were zero in the E. nitens population. Correlations among parental breeding values, predicted using data from the different populations, were generally low and non-significant, with two exceptions: predictions from the two E. globulus full-sib populations were significantly correlated (r=0.54, P = 0.001), as were predictions from the E. nitens seed orchard OP and full-sib population (r = 0.61, P = 0.08). There was some indication that superior parents of E. globulus native stand open-pollinated families also tended to have above-average breeding values based on the performance of intra-provenance full-sib offspring. The consequences of these results for exploitation of base-population collections from native stands are discussed.     

Genetic parameters of intra- and inter-specific hybrids of Eucalyptus globulus and E. nitens

Intra-specific hybrids within Eucalyptus nitens and E. globulus were compared directly with inter-specific E. nitens × globulus using common parents. Diameter (age 2, 4, 6, 10 years) and Pilodyn (age 6 years) were used as indirect measures of growth and wood density, respectively. Genetic parameters were estimated for all cross types and traits. A direct comparison of the general combining ability with the general hybridising ability was made. Heterosis was estimated for intra- and inter-specific hybrids. The intra-specific hybrids in both species exhibit intermediate heritabilities and levels of additive genetic variance. The inter-specific F1 E. nitens × globulus exhibited high incidence of abnormalities at young ages and high levels of later age mortality. The mean performance of surviving inter-specific F1 hybrids was generally intermediate for all traits, to varying degrees, between the parental intra-specific crosses, and there is little evidence for significant heterosis. Different provenances of E. globulus may exhibit different responses to hybridisation. In this case, the inter-specific F1 hybrids, using Taranna E. globulus, appear to perform worse on average than those using King Island provenance for growth traits. There is evidence that specific hybrid families are produced that outperform most of the pure species families for one or other of the traits examined; however, there is no reliable quantitative genetic method of predicting which parents should be used.     

Discovery, validation, and in silico functional characterization of EST-SSR markers in Eucalyptus globulus

Eucalyptus globulus is the most commonly planted hardwood species for pulpwood in temperate regions. We aimed to develop and characterize functional molecular markers for population genetic analyses and molecular breeding in this model tree species. Public expressed sequence tag (EST) databases were screened for nonredundant sequences to predict putative gene functions and to discover simple sequence repeats (EST-SSRs), which were then validated in E. globulus and six other Eucalyptus species. A total of 4,924 nonredundant sequences were identified from 12,690 updated E. globulus ESTs. Approximately 19.3% (952) were unigenes and contained 1,140 EST-SSR markers, which were mainly trimeric (58.6%). A set of 979 primers for putative SSR markers was designed after bioinformatic analysis. The predicted functions of these ESTs containing SSR were classified according to their gene ontology (GO) categories (biological process, molecular function, and cellular component). GO categories were assigned to 226 ESTs (30.2%). Most ESTs containing SSR (78.7%) had significant matches (E ≤ 10⁻⁵) with the nonredundant protein database using BLASTX. From a set of 56 random primer pairs, 37 could be validated in eight E. globulus genotypes and were also tested for cross-transferability to other six Eucalyptus species (Eucalyptus grandis, Eucalyptus saligna, Eucalyptus dunnii, Eucalyptus viminalis, Eucalyptus camaldulensis, Eucalyptus tereticornis). Seventeen polymorphic EST-SSR markers for E. globulus were evaluated in 60 unrelated trees, being representative of the species’ natural distribution. As a result, six highly informative markers were proposed for genetic diversity analyses, fingerprinting, and comparative population studies, between different species of E. globulus.     

Analysis of leaf oils from a Eucalyptus species trial

The volatile leaf oils were analysed from adult leaves of five Eucalyptus species growing in a common environment. The trial consisted of two provenances of the species E. globulus and one provenance each of E. nitens and E. denticulata from the southern blue gum group and two provenances each of the species E. delegatensis and E. regnans from the ash group. Oil yields from adult leaves of E. nitens (0.7% dry wt.) and E. denticulata (0.8%) were markedly lower than those from the other three species (3.0–6.1%). Volatile leaf oils of E. delegatensis and E. regnans were rich in α- and β-phellandrene, cis- and trans-p-menth-2-en-1-ol, while E. regnans was also rich in α-, β- and γ-eudesmol. In contrast, volatile leaf oils of E. globulus were rich in 1,8-cineole and α-pinene and E. denticulata rich in γ-terpinene and p-cymene. Oil composition of E. nitens was intermediate between E. globulus and E. denticulata. Differences in oil yield and oil composition between species indicated a strong genetic basis for these variables.     

Thermoregulation in three species of Afrotropical subterranean mole-rats (Rodentia: Bathyergidae) from Zambia and Angola and scaling within the genus Cryptomys

The thermoregulatory characteristics of three species of Cryptomys from Zambia and Angola are examined and, together with published data on four other species of Cryptomys from southern Africa, used to determine whether scaling occurs in this genus of subterranean rodents. The thermoregulatory properties of acclimated giant Zambian mole-rats, Cryptomys mechowi ( =267 g), Angolan mole-rats, Cryptomys bocagei ( =94 g) and Zambian common mole-rats Cryptomys hottentotus amatus ( =77 g) are as follows. Mean resting metabolic rates (RMRs) within the respective thermoneutral zones were 0.60±0.08 cm³ O₂ g^-1 h^-1 (n=12) for C. mechowi; 0.74±0.06 cm³ O₂ g^-1 h^-1 (n=8) for C. bocagei and 0.63±0.06 cm³O₂ g^-1 h^-1 (n=21) for C. h. amatus. The thermoneutral zones (TNZs) of all three species are narrow: 29–30°C for C. mechowi; 31.5–32.5°C for C. bocagei and 28–32° C for C. h. amatus. The increase in mean RMR at the lowest temperatures tested (15° C for C. mechowi, 18° C for C. bocagei and C. h. amatus) was 2.35, 2.2 and 3.82 times their RMR in the TNZ respectively. Body temperatures are low, 34±0.53° C (n=24) for C. mechowi, 33.7±0.32° C (n=20) for C. bocagei and 33.8±0.43° C (n=40) for C. h amatus. At the lower limit of thermoneutrality, conductances are 0.09±0.01 cm³ O₂ g^-1 h^-1 °C^-1 (n=30) in C. mechowi; 0.12±0.01 cm³ O₂ g^-1 h^-1 °C^-1 (n=20) in C. bocagei and 0.12±0.03 cm³ O₂ g^-1 h^-1 °C^-1 (n=32) in C. h. amatus. The range in mean body mass among the seven species of Cryptomys examined for scaling was 60 g (C. darlingi) to 267 g (C. mechowi). There is no clear relationship between RMR within the TNZ and body mass. The resultant relationship is represented by the power curve RMR=2.45 mass^-0.259.     

Moderate-density molecular maps of Eucalyptus urophylla S. T. Blake and E. tereticornis Smith genomes based on RAPD markers

Moderate-density molecular maps were constructed for the genomes of Eucalyptus urophylla S. T. Blake and E. tereticornis Smith using RAPD markers and an interspecific cross between the two species. One hundred and eighty-three primers were employed to generate 245 and 264 parent-specific markers in E. urophylla and E. tereticornis, respectively, as well as 49 parent-shared markers. The normally segregating markers, including 208 (84.9%) specific to maternal E. urophylla, 175 (66.3%) to paternal E. tereticornis, and 48 shared by both parents, were used for framework map construction for each parental species. For maternal E. urophylla, the linkage map consisted of 23 linkage groups, 160 framework markers, and 60 accessory markers, defining a total map distance of 1504.6 cM and an average interval of 11.0 ± 8.07 cM. For paternal E. tereticornis, the linkage map contained 23 linkage groups, 126 framework markers, and 92 accessory markers, defining a total map distance of 1035.7 cM and an average interval of 10.1 ± 7.23 cM. Genome length was estimated at 1585.7 and 1507.5 cM for E. urophylla and E. tereticornis, respectively, indicating map coverage of 94.9 and 68.7% of the corresponding genomes. Construction of such maps will be valuable for quantitative trait loci (QTLs) detection, marker-assisted selection (MAS), comparative mapping, and whole genome based fingerprint characterization in Eucalyptus breeding programs.     

Non-volatile components of the essential oil secretory cavities of Eucalyptus leaves: Discovery of two glucose monoterpene esters, cuniloside B and froggattiside A

The essential oils extracted from the embedded foliar secretory cavities of many Eucalyptus species are of economic value as pharmaceuticals and fragrance additives. Recent studies have indicated that Eucalyptus secretory cavities may not be exclusively involved in the biosynthesis and storage of essential oils. Therefore, we selected three species upon which to perform an examination of the contents of foliar secretory cavities: Eucalyptus froggattii, E. polybractea and E. globulus. This paper describes the isolation and structural characterization of two non-volatile glucose monoterpene esters, which we have named cuniloside B and froggattiside A, from within the secretory cavities of these species, and shows the presence of these compounds in solvent extracts of the leaves from two other species of Eucalyptus. Both compounds were found in high proportions relative to the essential oils extracted from the leaves. We propose that many other carbohydrate monoterpene esters previously isolated from bulk leaf extracts of various Eucalyptus species may also be localized within the non-volatile fraction of foliar secretory cavities.     

A chloroplast DNA hypervariable region in eucalypts

Eucalypt chloroplast DNA (cpDNA) provides useful markers for phylogenetic and population research including gene flow and maternity studies. All cpDNA studies in Eucalyptus to date have been based on the RFLP technique, which requires relatively large amounts of clean DNA. The objective of this study was to develop PCR-based cpDNA markers for Eucalyptus. The chloroplast genome of Eucalyptus, like that of most angiosperms, possesses inverted repeats (IR). The two junctions between the IRs and the large single copy (LSC) regions are defined as J_LA andJ_LB. The region surrounding the J_LA junction was sequenced from 26 Eucalyptus DNA samples (21 of E. globulus, plus 5 other species), andtheJ_LB region was sequenced using 5 of these samples. The samples were chosen to represent all major haplotypes identified in previous cpDNA RFLP studies. The J_LA products were 150–210 bp in size, while those fromJ_LB were approximately 500 bp in size. Eighteen mutations were scored in total. Extensive variation was found in the IR within the intergenic spacer between rpl2 and the IR/LSC junctions. Many of these characters were complex indels. One sample of E. globulus possessed a relatively large (38 bp) insertion which caused displacement of the IR/LSC junctions. This is the first report of intraspecific variation in the position of IR/LSC junctions; interspecific variation was also found. The LSC region near J_LB had a low rate of mutation and none were informative. The LSC region near J_LA possessed 2 informative mutations. The variation revealed from these sequences reflects the differentiation previously uncovered in an extensive RLFP analysis on the same samples. These results suggest that the J_LA region will provide very useful cpDNA polymorphisms for future studies in Eucalyptus. Received: 20 March 1999 / Accepted: 16 December 1999     

混交比例对桉树-乡土树种混交林优势树种叶片资源获取性状的影响

桉树-乡土树种混交林在提高林分生产力和生态系统功能等方面具有较大潜力。该研究以南亚热带4种桉树-乡土树种混交林(桉树与乡土树种混交比例分别为5:5、6:4、7:3、8:2)和桉树纯林为研究对象,研究了3种优势乡土树种华润楠(Machilus chinensis)、阴香(Cinnamomum burmannii)、灰木莲(Manglietia glauca)和速生树种尾叶桉(Eucalyptus urophylla)的叶片生理、结构和化学性状在不同比例混交林中的差异。结果表明,4优势造林树种的叶片性状存在明显的种间差异,其中灰木莲的比叶面积(SLA)、光合磷利用效率(PPUE)、单位质量叶片最大光合速率(A_mass)和蒸腾速率(T_mass)以及叶片养分含量最高,说明灰木莲采取资源获取型的生态策略;尾叶桉的SLA、A_mass、T_mass及叶片养分含量最低,但具有最高的PPUE,说明尾叶桉兼顾了资源获取型和保守型的物种特征。灰木莲与尾叶桉在SLA、A_mass、T_mass     

桉树杂交种对桉树枝瘿姬小蜂的抗性变异分析

植物种间杂交是一种普遍自然现象,杂交往往造成植物表型及生理变异,从而改变杂种抗虫性。与亲本种相比,杂种抗虫性可能增强或减弱,也有可能处于与亲本相似水平。初生、次生代谢物的质变与量变是引起杂种抗虫性变异的重要原因。近年来,桉树杂交育种已在世界范围内广泛应用并取得了显著成效,桉树杂交种间抗虫性表现参差不齐,因此,桉树是研究杂交种抗虫性变异机制的理想材料。以2个桉树杂交种巨细桉DH201-2、巨尾桉G9及桉树重要害虫桉树枝瘿姬小蜂为研究对象,比较了2个杂交种与其纯亲本种[(巨桉×细叶桉),(巨桉×尾叶桉)]间的抗虫性差异;同时,综合比较了品系间叶片性状(叶片厚度、含水率、比叶面积)、初生化合物(C、N、可溶性糖、可溶性蛋白)及次生化合物(总酚、单宁)差异,以研究桉树杂交种抗虫性变异的理化机制。结果表明:DH201-2感染桉树枝瘿姬小蜂的虫瘿数目显著高于其双亲本种,而G9上虫瘿数目显著低于其双亲本种。DH201-2与G9的叶片厚度与巨桉相近,而显著薄于另一亲本种。DH201-2叶片含水率显著高于细叶桉、与巨桉相近;G9叶片含水率则显著低于其双亲本种。相似的是,DH201-2和G9的比叶面积均显著高于其双亲本种。初生化合物方面,DH201-2叶片可溶性糖和可溶性蛋白含量均显著高于其亲本种,N含量则仅高于细叶桉;而G9叶片可溶性蛋白含量虽高于其双亲本种,可溶性糖含量则无显著差异,N含量显著低于其双亲本种。次生化合物方面,DH201-2叶片总酚和单宁含量显著低于其双亲本种,而G9则显著高于其双亲本种。因此,与其亲本种相比,DH201-2感虫性增加,而G9抗虫性增加;与桉树枝瘿姬小蜂发育相关的营养指标(如含水率、可溶性糖、N含量)及次生防御物质(如总酚、缩合单宁)在桉树杂交种组织内的含量差异影响了桉树杂交种对桉树枝瘿姬小蜂的抗性。在全球推行桉树杂交育种且桉树害虫数量逐年增加的大背景下,应加强对桉树杂交种抗虫性机制研究,为选育高抗品系及桉树产业可持续发展提供理论指导。     

Cold-induced photoinhibition affects establishment of Eucalyptus nitens (Deane and Maiden) Maiden and Eucalyptus globulus Labill

The effects of cold-induced photoinhibition on Eucalyptus globulus and Eucalyptus nitens seedlings were assessed between planting and age 23 weeks. The seedlings were subjected to four treatments before planting: non-hardened (NH) E. globulus and E. nitens, cold-hardened (CH) E. nitens, and nutrient-starved (NS) E. nitens. Seedlings were planted alongside established 1-year-old E. nitens saplings. The experimental site was at 350 m above sea level, which is considered marginal for the establishment of E. globulus plantations due to low mean minimum temperatures. Cold and sunny conditions after frost increased photoinhibition in the order: NH E. globulus > NH and CH E. nitens > NS and established E. nitens. As a result there was 20% mortality of NH E. globulus seedlings. NS E. nitens seedlings were severely photoinhibited and had high anthocyanin levels at planting; levels of photoinhibition decreased after planting, anthocyanin levels remained high and there was no mortality. Carotenoid levels were low in E. globulus compared to E. nitens treatments. It was concluded that cold-induced photoinhibition is a factor determining the range of environments where E. globulus can be successfully planted, and not frost tolerance alone. Anthocyanin was synthesised in response to increased photoinhibition. Anthocyanin levels were correlated to the severity of the photoinhibition. Thus, E. nitens seedlings nutrient starved in the nursery are pre-conditioned to photoinhibitory conditions experienced soon after planting. This treatment is a useful risk-management tool where cold-induced photoinhibition is likely to occur during seedling establishment.     

The influence of drought on the relationship between leaf and conducting sapwood area in Eucalyptus globulus and Eucalyptus nitens

 Development of the relationship between leaf area (A _l ) and sapwood area (A _s ) was investigated in two important hardwoods, Eucalyptus globulus (Labill) and E. nitens (Deane and Maiden) Maiden, growing in an experimental plantation established in a low rainfall zone (approx. 515 mm year^–1) of Tasmania. The experiment compared irrigated controls and a rainfed treatment which was subjected to cyclical summer droughts from age 1 to 6 years old. Leaf area and sapwood area were determined by destructive sampling at ages 2, 3 and 6 years old. There was no effect of stand age on A _l :A _s when sapwood area was measured at crown break. At age 3 years old A _l :A _s was significantly greater in the rainfed than the irrigated trees. It was concluded that this difference was due to earlier canopy closure in the irrigated trees. When the plantation was 6 years old A _l :A _s was significantly greater in the irrigated than the rainfed treatment. An analysis based on an equation which links A _l :A _s with transpiration and volumetric flow rate (Whitehead et al. 1984) was used to infer a positive correlation between stem hydraulic conductivity (k _h ) and water availability. Independent of water availability E. globulus maintained a higher A _l :A _s than E. nitens at all ages. Received: 20 March 1997 / Accepted: 30 December 1997     

Puccinia psidii infecting cultivated Eucalyptus and native myrtaceae in Uruguay

Eucalyptus or guava rust caused by Puccinia psidii is a serious disease of Eucalyptus and other Myrtaceae. In Uruguay, it has been previously found on Eucalyptus globulus and Psidium brasiliensis. Almost nothing is known regarding the occurrence of this pathogen on other Eucalyptus species or native Myrtaceae in that country. In this study, we determined the presence of P. psidii on Eucalyptus species and native Myrtaceae trees in Uruguay and evaluated the pathogenicity of specimens from native myrtaceous hosts on E. globulus and E. grandis. Phylogenetic analyses based on the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA operon were used to confirm pathogen identity. Comparisons of ITS sequences confirmed the identity of P. psidii on Eucalyptus globulus, E. grandis, Myrcianthes pungens, and Myrrhinium atropurpureum var. octandrum. This is the first report of P. psidii on M. atropurpureum var. octandrum. Pathogenicity tests showed that isolates from native Myrtaceae could infect both Eucalyptus species tested, indicating a strong biological relationship between both introduced and native Myrtaceae. This study supplies relevant field data, morphological information, molecular phylogenetic analyses and infection studies that contribute to a better understanding of an important and little studied pathogen.