Species of Mycosphaerellaceae and Teratosphaeriaceae on native Myrtaceae in Uruguay: evidence of fungal host jumps

Mycosphaerella species are well-known causal agents of leaf diseases on many economically and ecologically important plant species. In Uruguay, a relatively large number of Mycosphaerellaceae and Teratosphaeriaceae are found on Eucalyptus, but nothing is known of these fungi on native Myrtaceae. The aim of this study was to identify Mycosphaerellaceae and Teratosphaeriaceae species associated with leaf diseases on native Myrtaceae in Uruguay and to consider whether host jumps by the pathogen from introduced Eucalyptus to native Myrtaceae have occurred. Several native forests throughout the country were surveyed with special attention given to those located close to Eucalyptus plantations. Five species belonging to the Mycosphaerellaceae and Teratosphaeriaceae clades were found on native Myrtaceous trees and three of these had previously been reported on Eucalyptus in Uruguay. Those occurring both on Eucalyptus and native Myrtaceae included Pallidocercospora heimii, Pseudocercospora norchiensis, and Teratosphaeria aurantia. In addition, Mycosphaerella yunnanensis, a species known to occur on Eucalyptus but not previously recorded in Uruguay, was found on leaves of two native Myrtaceous hosts. Because most of these species occur on Eucalyptus in countries other than Uruguay, it appears that they were introduced in this country and have adapted to be able to infect native Myrtaceae. These apparent host jumps have the potential to result in serious disease problems and they should be carefully monitored.     

桉属植物非挥发性化学成分和药理活性研究进展

桉属(Eucalyptus L. Herit)是桃金娘科(Myrtaceae)的大属,该属约600余种,主要分布于世界各地热带亚热带地区。我国引入品种较多,主要分布于华南地区,其中广东和广西为桉树的主要种植基地。桉属植物具有较多的工业价值,其木材、叶、果实等是化学工业、香料、医药领域的重要原料,可用作开发高性能桉木重组材、竹桉复合材料、造浆与造纸等。桉属植物作为民间药材被使用,具有抑菌消炎、疏风解热、防腐止痒等功效,其药理研究表明,桉属植物具有良好的抗氧化、抗炎、抗菌、抗病毒、抗肿瘤、抗心血管疾病等药理活性。该研究通过查阅近三十年桉属植物相关的国内外文献报道,对桉属植物不同部位的421个非挥发性化学成分及其药理活性等进行了较详细的分类阐述,其中黄酮类化合物共73个、有机酸化合物共61个、萜类化合物共45个、多酚类化合物共229个、脂肪醇类化合物共13个,药理活性多集中在抗氧化、抗菌、抗病毒、抗肿瘤等,但相关机制仍需进一步阐明。该文重点关注桉属植物的药用部位,充分发掘其药用价值,开展临床转化和新药研究工作,为今后桉属植物的进一步研究、开发和利用提供科学依据。     

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.     

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.     

Gene flow of the canker pathogen Botryosphaeria australis between Eucalyptus globulus plantations and native eucalypt forests in Western Australia

Abstract The eucalypt plantation industry in Western Australia provides a unique opportunity to study the movement of pathogens between closely related host taxa. Eucalyptus globulus, a native to Tasmania and south‐eastern Australia, is the predominant species in Western Australian plantations, often being planted adjacent to native forest containing Eucalyptus marginata and Eucalyptus diversicolor. Since the commencement of the plantation industry 20 years ago, several fungal species, previously known only to eastern Australia or overseas, have been reported on E. globulus in Western Australia. Botryosphaeria australis is a newly described species, recently found causing cankers on Acacia spp. in eastern Australia. However, during a routine survey, B. australis was found to be the predominant species associated with E. globulus plantations and native Eucalyptus spp. in Western Australia. In this study, six short simple repeat markers were used to evaluate genetic diversity and gene flow between collections of B. australis from native eucalypt forest and E. globulus plantations at two locations in south‐western Australia. In both cases, there was no restriction to gene flow between the plantations and the adjacent native forest. Botryosphaeria australis has now been isolated from a wide range of hosts across south‐western Australia and was not isolated from E. globulus in Tasmania or South Australia. This extensive distribution and host range suggests B. australis is native to Western Australia. This study demonstrates the ability of a pathogen to move between plantation and forests.     

Rust disease of eucalypts,caused by Puccinia psidii,did not originate via host jump from guava in Brazil

The rust fungus, Puccinia psidii, is a devastating pathogen of introduced eucalypts (Eucalyptus spp.) in Brazil where it was first observed in 1912. This pathogen is hypothesized to be endemic to South and Central America and to have first infected eucalypts via a host jump from native guava (Psidium guajava). Ten microsatellite markers were used to genotype 148 P. psidii samples from eucalypts and guava plus five additional myrtaceous hosts across a wide geographic range of south‐eastern Brazil and Uruguay. Principal coordinates analysis, a Bayesian clustering analysis and a minimum‐spanning network revealed two major genetic clusters among the sampled isolates, one associated with guava and another associated with eucalypts and three additional hosts. Multilocus genotypes infecting guava differed by multiple mutational steps at eight loci compared with those infecting eucalypts. Approximate Bayesian computation revealed that evolutionary scenarios involving a coalescence event between guava‐ and eucalypt‐associated pathogen populations within the past 1000 years are highly unlikely. None of the analyses supported the hypothesis that eucalypt‐infecting P. psidii in Brazil originated via host jump from guava following the introduction of eucalypts to Brazil approximately 185 years ago. The existence of host‐associated biotypes of P. psidii in Brazil indicates that this diversity must be considered when assessing the invasive threat posed by this pathogen to myrtaceous hosts worldwide.     

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     

Contribution of the saprobic fungi Trametes versicolor and Trichoderma harzianum and the arbuscular mycorrhizal fungi Glomus deserticola and G. claroideum to arsenic tolerance of Eucalyptus globulus

The presence of high concentrations of arsenic (As) decreased the shoot and root dry weight, chlorophyll and P and Mg content of Eucalyptus globulus colonized with the arbuscular mycorrhizal (AM) fungi Glomus deserticola or G. claroideum, but these parameters were higher than in non-AM plants. As increased the percentage of AM length colonization and succinate dehydrogenase (SDH) activity in the root of E. globulus. Trichoderma harzianum, but not Trametes versicolor, increased the shoot and root dry weight, chlorophyll content, the percentage of AM root length colonization and SDH activity of E. globulus in presence of all As concentrations applied to soil when was inoculated together with G. claroideum. AM fungi increased shoot As and P concentration of E. globulus to higher level than the non-AM inoculated controls. The contribution of the AM and saprobe fungi to the translocation of As from root to shoot of E. globulus is discussed.     

Phytophthora captiosa sp. nov. and P. fallax sp. nov. causing crown dieback of Eucalyptus in New Zealand

A locally severe crown disease of exotic plantation Eucalyptus trees has been recorded periodically in New Zealand since 1986. Symptoms include leaf spots, petiole infection and twig and small branch lesions. Outbreaks of disease are episodic and individual trees may show marked variation in crown symptoms ranging from unaffected to total defoliation. Two previously unknown species of Phytophthora are associated with the disease. These are described and formally designated here as P. captiosa, from Eucalyptus botryoides and E. saligna; and P. fallax, from E. delegatensis, E. fastigata, E. nitens and E. regnans. Both P. captiosa and P. fallax have non-papillate, non-caducous sporangia and both are self-fertile. Phylogenetic analysis on the basis of ITS rDNA sequence data indicates they are closely related to each other but evolutionarily distant from the majority of described Phytophthora taxa. They share a common ancestor with another assemblage of Phytophthora lineages that includes P. insolita, P. macrochlamydospora and P. richardiae. Sporulation of P. captiosa and P. fallax has not been observed in the field. The mode of infection and spread of these non-caducous Phytophthora species in the eucalypt tree canopy remains unknown. This issue, and the possible geographic origins of these two Phytophthora species are discussed.     

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.     

High synteny and colinearity among Eucalyptus genomes revealed by high-density comparative genetic mapping

Understanding genome differentiation is important to compare and transfer genomic information between taxa, such as from model to non-model organisms. Comparative genetic mapping can be used to assess genome differentiation by identifying similarities and differences in chromosome organization. Following release of the assembled Eucalyptus grandis genome sequence (January 2011; ), a better understanding of genome differentiation between E. grandis and other commercially important species belonging to the subgenus Symphyomyrtus is required. In this study, comparative genetic mapping analyses were conducted between E. grandis, Eucalyptus urophylla, and Eucalyptus globulus using high-density linkage maps constructed from Diversity Array Technology and microsatellite molecular markers. There were 236–393 common markers between maps, providing the highest resolution yet achieved for comparative mapping in Eucalyptus. In two intra-section comparisons (section Maidenaria–E. globulus and section Latoangulatae–E. grandis vs. E. urophylla), ∼1% of common markers were non-syntenic and within chromosomes 4.7–6.8% of markers were non-colinear. Consistent with increasing taxonomic distance, lower synteny (6.6% non-syntenic markers) was observed in an inter-section comparison between E. globulus and E. grandis × E. urophylla consensus linkage maps. Two small chromosomal translocations or duplications were identified in this comparison representing possible genomic differences between E. globulus and section Latoangulatae species. Despite these differences, the overall high level of synteny and colinearity observed between section Maidenaria–Latoangulatae suggests that the genomes of these species are highly conserved indicating that sequence information from the E. grandis genome will be highly transferable to related Symphyomyrtus species.     

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.     

Positioning of the major locus for <Emphasis Type="Italic">Puccinia psidii</Emphasis> rust resistance (<Emphasis Type="Italic">Ppr1</Emphasis>) on the <Emphasis Type="Italic">Eucalyptus</Emphasis> reference map and its validation across unrelated pedigrees

In this report the major locus for Puccinia psidii rust resistance, Ppr1, was positioned on the reference genetic map for Eucalyptus. Additionally, its position was validated by association genetics in a related and two unrelated pedigrees involving different Eucalyptus grandis resistant trees crossed to individuals of two other species, Eucalyptus tereticornis and Eucalyptus camaldulensis. These results are consistent with the hypothesis that Ppr1 controls a large proportion of the variation for rust resistance, strengthening its role as a major locus in Eucalyptus and providing its unequivocal genomic position on linkage group 3. A localized map with 19 microsatellite loci was built around Ppr1. Multiallelic profiles were observed at several mapped microsatellites suggesting recent tandem duplications in the genomic landscape surrounding Ppr1. Markers EMBRA125 and EMBRA1071 flank Ppr1 at 9.5% and 7% recombination, respectively, and were found to be in linkage equilibrium in a E. grandis breeding population, consistent with the expectations in outcrossed Eucalyptus. Their potential use for MAS will specifically be directed to identifying resistant offspring of P. psidii resistant parent trees that are heterozygous at Ppr1. In these circumstances, a significant amount of LD is expected to occur between specific alleles at flanking microsatellites and the resistance allele at Ppr1. Moreover, the positional information of Ppr1 paves the way for prospective undertakings in this genomic region with the upcoming availability of a draft genome for E. grandis.     

Insect pests of Tasmanian blue gum,Eucalyptus globulus globulus,in south‐western Australia: History,current perspectives and future prospects

Trends in, and potential causes of, insect pest problems of the Tasmanian blue gum, Eucalyptus globulus globulus, in south‐western Australia are reviewed. Historical evidence suggests that insect pest problems of E. g. globulus in south‐western Australia have greatly increased in the last 10 years, which corresponds to a time of rapid expansion of the blue gum industry in the region. Current major establishment pests include the African black beetle, Heteronychus arator, spring beetles, Liparetrus spp. and Heteronyx spp., and the wingless grasshopper, Phaulacridium vittatum. Current major pests of established trees are the Eucalyptus weevil, Gonipterus scutellatus, and chrysomelid beetles, Chrysophtharta spp. and Cadmus excrementarius. The occurrence of these insects on an introduced eucalypt is not unexpected because insect‐rich native eucalypt forests dominate the landscape where E. g. globulus plantations are grown. Insect damage may also be exacerbated because E. g. globulus is grown as a monoculture.     

Novel hosts of the Eucalyptus canker pathogen Chrysoporthe cubensis and a new Chrysoporthe species from Colombia

The pathogen Chrysoporthe cubensis (formerly Cryphonectria cubensis) is best known for the important canker disease that it causes on Eucalyptus species. This fungus is also a pathogen of Syzygium aromaticum (clove), which is native to Indonesia, and like Eucalyptus, is a member of Myrtaceae. Furthermore, C. cubensis has been found on Miconia spp. native to South America and residing in Melastomataceae. Recent surveys have yielded C. cubensis isolates from new hosts, characterized in this study based on DNA sequences for the ITS and β-tubulin gene regions. These hosts include native Clidemia sericea and Rhynchanthera mexicana (Melastomataceae) in Mexico, and non-native Lagerstroemia indica (Pride of India, Lythraceae) in Cuba. Isolates from these hosts and areas group in the sub-clade of C. cubensis accommodating the South American collections of the fungus. This sub-clade also includes isolates recently collected from Eucalyptus in Cuba, which are used to epitypify C. cubensis. New host records from Southeast Asia include exotic Tibouchina urvilleana from Singapore and Thailand and native Melastoma malabathricum (Melastomataceae) in Sumatra, Indonesia. Consistent with their areas of occurrence isolates from the latter collections group in the Asian sub-clade of C. cubensis. DNA sequence comparisons of isolates from Tibouchina lepidota in Colombia revealed that they represent a new sub-clade within the greater Chrysoporthe clade. Isolates in this clade are described as Chrysoporthe inopina sp. nov., based on distinctive morphological differences.     

Recurrent nuclear DNA introgression accompanies chloroplast DNA exchange between two eucalypt species

Numerous studies within plant genera have found geographically structured sharing of chloroplast (cp) DNA among sympatric species, consistent with introgressive hybridization. Current research is aimed at understanding the extent, direction and significance of nuclear (nr) DNA exchange that accompanies putative cpDNA exchange. Eucalyptus is a complex tree genus for which cpDNA sharing has been established between multiple species. Prior phylogeographic analysis has indicated cpDNA introgression into the widespread forest species Eucalyptus globulus from its rare congener E. cordata. In this study, we use AFLP markers to characterize corresponding nrDNA introgression, on both a broad and fine spatial scale. Using 388 samples we examine (i) the fine‐scale spatial structure of cp and nrDNA introgression from E. cordata into E. globulus at a site in natural forest and (ii) broad‐scale patterns of AFLP marker introgression at six additional mixed populations. We show that while E. globulus and E. cordata retain strongly differentiated nuclear gene pools overall, leakage of nrDNA occurs at mixed populations, with some AFLP markers being transferred to E. globulus recurrently at different sites. On the fine scale, different AFLP fragments show varying distances of introgression into E. globulus, while introgression of cpDNA is extensive. The frequency of E. cordata markers in E. globulus is correlated with spatial proximity to E. cordata, but departs from expectations based on AFLP marker frequency in E. cordata, indicating that selection may be governing the persistence of introgressed fragments in E. globulus.     

Plant architecture,growth and biomass allocation effects of the invasive pathogen myrtle rust (Austropuccinia psidii) on Australian Myrtaceae species after fire

In 2010, the parasitic fungus Austropuccinia psidii (myrtle rust) was detected in Australia. Austropuccinia psidii infects immature growth of myrtaceous species. Many of Australia’s myrtaceous species occur within fire‐prone vegetation communities and have the capacity to resprout after fire. Therefore, it is likely that new post‐fire growth may be vulnerable to A. psidii infection, causing subsequent flow‐on effects to species’ persistence and community dynamics. The aim of this study was to test the impacts of A. psidii on native Australian Myrtaceae species after fire. We grew eight native susceptible species in a glasshouse experiment before burning them and inoculating the resprouting new growth of half the plants with A. psidii. We assessed the effect of A. psidii on the architecture, growth and biomass allocation of our study species. Although general patterns were observed across species, results were found to be species‐specific. Austropuccinia psidii significantly reduced the height of two of the eight species (Callistemon citrinus and Eucalyptus moluccana), but none of the species had increased branching. As expected, specific leaf area was lower (9%) in inoculated plants – although only significant for C. citrinus and E. dalrympleana – and leaf biomass was greater (15%), but significant for Angophora costata only. Finally, biomass allocation did not significantly differ between infection treatments. We can conclude that the effect of A. psidii infection on fire‐damaged plants has significant impacts on plants at the species level, which may have flow‐on effects at the community level, especially after repeated infections. Furthermore, these impacts may be exacerbated in the future under climate change, as the predicted increase in frequency and intensity of fires across Australia will result in more frequent new growth availability, providing more opportunities for A. psidii infection.     

Impacts of the invasive fungus Austropuccinia psidii (myrtle rust) on three Australian Myrtaceae species of coastal swamp woodland

Exotic fungal pathogens can substantially affect individuals and populations of susceptible native plant species, potentially resulting in changes in community structure and composition. Austropuccinia psidii (myrtle rust) is a pathogenic fungus native to South America that affects species in the plant family Myrtaceae. The pathogen was introduced accidentally to Australia and first detected in NSW in April 2010. Ecological impacts have been poorly studied in the native range of A. psidii and even less in its Australian introduced range. In order to assess the potential impact of A. psidii on coastal swamp woodland, two glasshouse experiments were conducted using three co‐occurring species: Melaleuca quinquenervia, Leptospermum laevigatum and Baeckea linifolia. Plants of each species were grown individually (Experiment 1) and in mixed species assemblages (Experiment 2), with half inoculated with A. psidii and the other half remaining as controls. Infection level was assessed and impact on seedling survival and growth recorded. In both experiments L. laevigatum and M. quinquenervia seedlings were heavily infected and showed high degrees of susceptibility with negative effects on growth (height, biomass and number of leaves). In contrast, no B. linifolia seedling presented visible symptoms of disease, although seedlings showed reduced growth. Melaleuca quinquenervia seedlings had greater infection levels and suffered greater growth reductions than L. laevigatum in both experiments. However, there was no significant difference in the relative abundance of the three species in the mixed‐species experiment. This study provides a better understanding of the potential impacts of A. psidii in this vegetation community and has significant implications for the conservation and management of Australian Myrtaceae‐dominated plant communities generally.     

Leaf gas exchange and chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence of <Emphasis Type="Italic">Eucalyptus urophylla</Emphasis> in response to <Emphasis Type="Italic">Puccinia psidii</Emphasis> infection

One of the most important diseases of eucalyptus plantations is caused by the rust fungus Puccinia psidii. While the genetic basis of rust resistance has been addressed recently, little is known about the physiological aspects of Eucalyptus–P. psidii interaction. In order to fill this gap, we undertook a study investigating the effects of P. psidii infection on photosynthetic processes of two E. urophylla clones with contrasting resistance to the pathogen. Our results show that gas exchange and chlorophyll a fluorescence parameters were virtually unaffected in the resistant clone. In the susceptible clone, photosynthetic rates were chiefly constrained by biochemical limitations to carbon fixation. Photosynthesis was impaired only in symptomatic tissues since the reductions in photosynthetic rates were proportional to the diseased leaf area. Rust infection provoked chronic photoinhibition to photosynthesis in the susceptible clone. Overall, differences in the ability for light capture, use and dissipation may play a significant role in explaining the clonal differences in Eucalyptus in response to P. psidii infection. To our knowledge, this is the first report of the effect of rust infection on gas exchange and chlorophyll a fluorescence parameters in Eucalyptus.