Search

In agricultural systems, responsive management can mitigate the effects of risk and uncertainty by facilitating adaptation to changing conditions. A tool for evaluating management systems while accounting for risk and uncertainty is Probabilistic Cost Benefit Analysis (PCBA). This study used PCBA to contrast a new responsive disease management strategy against an existing prescriptive strategy. Fungicide application to prevent myrtle rust (MR) in NZ plant nurseries was used as a case study to test if the expected benefits of the responsive strategy justified the investment in potentially more frequent and costlier disease control. A MR risk generator was used to simulate disease progression. Empirical MR risk distribution functions were sampled to stochastically compare net benefits across scenarios, highlighting the potential impact of infrequent but significant disease incursions. Our results showed that the risk-based strategy was more effective at controlling the disease, especially for susceptible myrtle species in high-risk locations. The findings highlighted the essential role of fungicides in propagating highly MR-susceptible species, and that disease management, when responsive to risk, enhanced the efficiency of fungicide use. The Responsive strategy is discussed as an effective management option for nurseries under uncertainty of significant MR incursions. However, in less risky scenarios, the benefits of the responsive strategy were moderate, and operational considerations may favour the standard calendar-based approach. In such cases, the method provided here can help estimate the appropriate fungicide application interval and the associated MR risk. [ABSTRACT FROM AUTHOR]

Aotearoa New Zealand's swamp forests have experienced significant habitat loss in fewer than two hundred years. Many of the country's tree species are endemic with sparse to no genetic information available to underpin conservation strategies. Syzygium maire, Aotearoa's only endemic Syzygium species, is a culturally and ecologically important component of swamp forest habitats. Unfortunately, populations of S. maire have been greatly reduced, heavily fragmented and are susceptible to the emergent pathogen Austropuccinia psidii (myrtle rust), posing eminent danger of a further decline of the species. We sought to develop genomic resources to inform conservation management of S. maire. To this end, we used long read, high accuracy sequencing technology to produce a highly complete reference quality genome for S. maire. The genome sequence was named 'Ngā Hua o te Ia Whenua' by the local Māori tribe where the tree used for genome sequencing grows. We assess whether genome-level divergence with other Myrtaceae may have followed geographic isolation of the species. We detect conservation of large scale synteny between three Syzygium species and Eucalyptus grandis, providing support for the stability of Syzygium genomes across evolutionary time. We annotate genes implicated in fungal pathogen defence, identifying several hundred putative NLR genes, including putative homologs of previously identified Austropuccinia psidii resistance genes. Finally, we evaluate the genetic relationships of individuals of a small, isolated population of trees. We find evidence of high levels of kinship and inbreeding within small and isolated S. maire populations, informing local-scale conservation strategies for the species. Our findings enable practical conservation actions and provide resources for larger scale studies of S. maire and other Syzygium species in the future. [ABSTRACT FROM AUTHOR]

Planting of resistant clones is the main control strategy for rust caused by Austropuccinia psidii on eucalypts in Brazil. Phenotyping for resistance to rust is performed at the last stage of the breeding programme on genetic material preselected for growth and industrial traits, which therefore may include susceptible genotypes. An alternative way to increase the frequency of resistant individuals in the breeding population is to perform resistance phenotyping during the initial stages of the programme. However, the impact of this approach on other characteristics considered as priority in the selection of genetic material should be assessed. In this study, we evaluated whether early selection for resistance to rust influenced total diameter at breast height (DBH), height (TH), average annual increment (IMA) and basic wood density (BWD), which are important selection criteria in eucalypt breeding. For this, a total of 6 703 plants from 70 full-sib progenies of Eucalyptus grandis, E. urophylla and hybrids of these species were phenotyped for rust resistance before transplanting, under controlled conditions, and again at seven months after transplanting, under field conditions and natural infection. Subsequently, the breeding population was evaluated for BWD indirectly through pilodyn penetration at 24 months after planting, and for DBH, TH and MAI at 37 months. Considering the final phenotype, 25.3% individuals were classified as resistant and 74.7% were susceptible to rust. Comparative genetic analyses between resistant and susceptible individuals showed that selection for resistance, performed early, did not influence DBH, TH, MAI or BWD traits. Thus, the early selection of resistant genotypes speeds up the exclusion of susceptible genotypes, saving time and resources in the development of new commercial clones without interfering with other important traits for tree breeding. [ABSTRACT FROM AUTHOR]

Faced with growing biosecurity risks and threats, countries worldwide seek to protect their biodiversity from ecosystem degradation and loss. Biosecurity surveillance of plant pathogens and the diseases they cause is fundamental for management and eradication of these risks. To date, the surveillance systems in Aotearoa New Zealand have reflected empirical scientific principles and have been largely devoid of mātauranga and te ao Māori, which have seldom been regarded as valid or relevant knowledge systems to inform biosecurity. Because of this, mana whenua themselves have been disconnected from these systems. The inclusion of mana whenua and their mātauranga is important, not only to recognise their role and rights as indigenous peoples of Aotearoa New Zealand, but because it is through place-based approaches that better biodiversity and environmental outcomes can be achieved. Here, we describe a mātauranga Māori framework for surveillance (MMFS) of plant pathogens, which introduces the principles and methodologies that aim to elevate mana whenua and mātauranga research into the biosecurity and science systems. The MMFS facilitates the co-existence of mātauranga and empirical scientific knowledge without the need for inter-dependent validation, on the assumption that this will lead to better research and operational outcomes. It addresses issues around data ownership and sovereignty, informed consent, and cultural licence. We present a case study where the MMFS has been applied to research initiatives aimed at addressing myrtle rust and kauri dieback in Aotearoa New Zealand. The MMFS informed the development of a data storage platform, which anchors data to the place of origin, recognising its provenance and giving effect to Māori data sovereignty. This process ensures mana whenua have timely access and use of existing and emergent data. Following the principles of the MMFS, we developed and used a "proof of pathogen absence" tool to co-design with mātauranga environmental experts a risk-based surveillance plan for the purpose of demonstrating freedom from disease in areas where a pathogen has not been detected. The MMFS provides a way of planning and implementing environmental surveillance that can be applied to the full range of environmental problems internationally where indigenous populations are involved. [ABSTRACT FROM AUTHOR]

Myrtle rust, caused by Austropuccinia psidii, has been associated with more than 480 plant species belonging to the family Myrtaceae. Intraspecific variability in pathogenicity has been reported among isolates of A. psidii from different hosts. However, there are few studies that have comparatively quantified the disease in guava (Psidium guajava) and rose apple (Syzygium jambos). The objective of this work was to quantify the pathogenic variability of A. psidii isolates collected from guava and rose apple in Brazil and to investigate the mechanisms of infection and colonization of the pathogen at the cellular level. The monocyclic components of the rust disease were evaluated on young leaves of rose apple and guava plants cross‐inoculated with isolates from rose apple and guava. Pathogenic specialization of both A. psidii isolates for their respective hosts was confirmed in this work. The guava A. psidii isolate was able to infect and colonize rose apple leaf tissues but no sporulation occurred. Similarly, the rose apple A. psidii isolate infected guava plants but did not sporulate. Confocal laser scanning microscopy revealed that lobed haustoria were present within rose apple leaves at 2 days post‐inoculation (dpi) with both isolates, which resulted in intense mesophyll colonization for both interactions at 9 dpi. The latter is remarkable because infection of rose apple with the guava A. psidii isolate did not result in mature rust pustules. [ABSTRACT FROM AUTHOR]

Austropuccinia psidii causes rust disease on species within the family Myrtaceae. It was first detected in Australia in 2010, with the first detection in Western Australia in 2022. While species within the genus Melaleuca from eastern Australia show variable responses to the pathogen, little is known of the response of species from Western Australia. This study established that 13 previously unscreened species of Melaleuca, including Threatened and Priority listed species that were grown from seeds sourced from Western Australian populations, were susceptible four months post-germination to the pandemic strain of the pathogen. The proportion of highly susceptible plants within a single species ranged from 2 to 94%, with several species displaying highly variable levels of resistance to A. psidii. These results highlight the importance of disease screening and may direct conservation efforts. [ABSTRACT FROM AUTHOR]

Faced with growing biosecurity risks and threats, countries worldwide seek to protect their biodiversity from ecosystem degradation and loss. Biosecurity surveillance of plant pathogens and the diseases they cause is fundamental for management and eradication of these risks. To date, the surveillance systems in Aotearoa New Zealand have reflected empirical scientific principles and have been largely devoid of mātauranga and te ao Māori, which have seldom been regarded as valid or relevant knowledge systems to inform biosecurity. Because of this, mana whenua themselves have been disconnected from these systems. The inclusion of mana whenua and their mātauranga is important, not only to recognise their role and rights as indigenous peoples of Aotearoa New Zealand, but because it is through place-based approaches that better biodiversity and environmental outcomes can be achieved. Here, we describe a mātauranga Māori framework for surveillance (MMFS) of plant pathogens, which introduces the principles and methodologies that aim to elevate mana whenua and mātauranga research into the biosecurity and science systems. The MMFS facilitates the co-existence of mātauranga and empirical scientific knowledge without the need for inter-dependent validation, on the assumption that this will lead to better research and operational outcomes. It addresses issues around data ownership and sovereignty, informed consent, and cultural licence. We present a case study where the MMFS has been applied to research initiatives aimed at addressing myrtle rust and kauri dieback in Aotearoa New Zealand. The MMFS informed the development of a data storage platform, which anchors data to the place of origin, recognising its provenance and giving effect to Māori data sovereignty. This process ensures mana whenua have timely access and use of existing and emergent data. Following the principles of the MMFS, we developed and used a “proof of pathogen absence” tool to co-design with mātauranga environmental experts a risk-based surveillance plan for the purpose of demonstrating freedom from disease in areas where a pathogen has not been detected. The MMFS provides a way of planning and implementing environmental surveillance that can be applied to the full range of environmental problems internationally where indigenous populations are involved.

IntroductionSyzygium maire is a threatened Myrtaceae tree species endemic to New Zealand. Due to its highly recalcitrant seed, cryopreservation is the only viable long-term ex situ conservation option for this species. Our previous attempts to cryopreserve the embryonic axis (EAs) of S. maire were unsuccessful but did provide a better understanding of desiccation behavior, biochemical composition, oxidative status, and ultrastructural changes associated with desiccation in EAs.MethodsWe incorporated this knowledge with biophysical information to investigate two advanced cryopreservation technologies: a droplet vacuum infiltration vitrification (DVIV) method and a novel metal-mesh vacuum infiltration vitrification (MVIV) method using Plant Vitrification Solution 2 (PVS2) for cryopreservation of the EAs.ResultsThe PVS2 treatment at room temperature (~20°C) proved phytotoxic with extended PVS2 incubation significantly reducing EA survival. No EAs survived cryopreservation using DVIV, however MVIV resulted in post-cryopreservation survival of up to 19% following PVS2 incubation for 20 min. Biophysical thermal analysis using Differential Scanning Calorimetry revealed a 15-fold reduction in ice crystallization following incubation in PVS2 for 20 min or more, with all freezable water removed after 60 min incubation.DiscussionThese results present a significant advance in being able to successfully cryopreserve S. maire EAs. The findings from this study will aid the development of cryopreservation protocols for other extremely recalcitrant seeded species, many of which are threatened with extinction due to climate change, plant pathogens, and habitat destruction.

Austropuccinia psidii is a biotrophic fungus that causes myrtle rust. First described in Brazil, it has since spread to become a globally important pathogen that infects more than 480 myrtaceous species. One of the most important commercial crops affected by A. psidii is eucalypt, a widely grown forestry tree. The A. psidii–Eucalyptus spp. interaction is poorly understood, but pathogenesis is likely driven by pathogen-secreted effector molecules. Here, we identified and characterized a total of 255 virulence effector candidates using a genome assembly of A. psidii strain MF-1, which was recovered from Eucalyptus grandis in Brazil. We show that the expression of seven effector candidate genes is modulated by cell wax from leaves sourced from resistant and susceptible hosts. Two effector candidates with different subcellular localization predictions, and with specific gene expression profiles, were transiently expressed with GFP-fusions in Nicotiana benthamiana leaves. Interestingly, we observed the accumulation of an effector candidate, Ap28303, which was upregulated under cell wax from rust susceptible E. grandis and described as a peptidase inhibitor I9 domain-containing protein in the nucleus. This was in accordance with in silico analyses. Few studies have characterized nuclear effectors. Our findings open new perspectives on the study of A. psidii–Eucalyptus interactions by providing a potential entry point to understand how the pathogen manipulates its hosts in modulating physiology, structure, or function with effector proteins. [ABSTRACT FROM AUTHOR]

Myrtaceous plants such as Eucalyptus and Melaleuca are economically and ecologically important. Many species, including M. alternifolia and M. quinquenervia, are known to be susceptible to the exotic rust fungus Austropuccinia psidii. Identifying the molecular basis of resistance against A. psidii would assist in incorporating resistance to this pathogen for industries producing essential oils and for re-afforestation. Nucleotide-binding sites and leucine-rich repeat (NBS-LRR) genes have been identified as important candidates in several studies. It is unknown whether resistance against A. psidii is conserved among, as well as within species of Myrtaceae. Therefore, this study aimed to identify whether candidate NBS-LRR genes that may have contributed to defence in M. alternifolia and M. quinquenervia are closely related to candidate NBS-LRR genes within the A. psidii resistance loci of E. grandis and E. globulus. NBS-LRR sequences of M. alternifolia, M. quinquenervia and E. grandis were subjected to phylogenetic analysis. Although no candidate NBS-LRR genes for A. psidii defence from M. alternifolia or M. quinquenervia were found to be orthologous to NBS-LRR genes within the E. grandis Ppr1 locus, one candidate NBS-LRR gene for defence against A. psidii in M. quinquenervia was orthologous to a candidate NBS-LRR within Ppr2 from E. globulus. Phylogenetic analysis of multiple species of Myrtaceae also revealed that NBS-LRR genes within Ppr1 may not be the result of recent gene duplications and were highly diverse. [ABSTRACT FROM AUTHOR]

Context: Metrosideros bartlettii is one of the most threatened trees in New Zealand and with less than 14 individuals spread across three populations, the species is at high risk of extinction. Despite reproductive failure being identified as one of the factors contributing to population decline, little is known about its pollination biology. Aim: The current study aimed to gain knowledge of the reproductive biology of M. bartlettii by using trees in cultivation of which origin is known. Methods: We tested the effect of self-pollination, cross-pollination and hybridisation treatments on reproductive output. In addition, the viability of fresh pollen was determined for each tree and the impact of desiccation and storage temperature (5°C, −18°C and −196°C) on pollen viability assessed. Key results: Metrosideros bartlettii was found to be highly self-incompatible with seed formed via autonomous self-pollination having low viability. Hybridisation with Metrosideros excelsa , another native species commonly found in cultivation, produced viable seeds, but seedlings failed to survive. Pollen viability differed significantly among trees, and pollen stored at −18°C and −196°C retained viability after 6 months. Conclusion: Metrosideros bartlettii is self-incompatible and cross-pollination is required to increase seed production and supplement wild populations. Implications: Trees in cultivation provide a valuable tool for the conservation of M. bartlettii. However, cross-pollination is essential to prevent hybridisation and ensure genetically robust seed. Long-term storage of pollen at the temperatures determined here will help to overcome challenges in cross-pollination of trees that are spatially and geographically isolated. Metrosideros bartlettii is a critically endangered tree represented by less than 14 individuals in the wild. Due to its self-incompatible breeding system, pollen from an individual from a different population is required to produce viable seed. Short- and long-term pollen storage helps to overcome challenges in cross-pollination both in the wild and in ex situ collections. [ABSTRACT FROM AUTHOR]

Rust fungi (Pucciniales) are a diverse group of plant pathogens in natural and agricultural systems. They pose ongoing threats to the diversity of native flora and cause annual crop yield losses. Agricultural rusts are predominantly managed with fungicides and breeding for resistance, but new control strategies are needed on non‐agricultural plants and in fragile ecosystems. RNA interference (RNAi) induced by exogenous double‐stranded RNA (dsRNA) has promise as a sustainable approach for managing plant‐pathogenic fungi, including rust fungi. We investigated the mechanisms and impact of exogenous dsRNA on rust fungi through in vitro and whole‐plant assays using two species as models, Austropuccinia psidii (the cause of myrtle rust) and Coleosporium plumeriae (the cause of frangipani rust). In vitro, dsRNA either associates externally or is internalized by urediniospores during the early stages of germination. The impact of dsRNA on rust infection architecture was examined on artificial leaf surfaces. dsRNA targeting predicted essential genes significantly reduced germination and inhibited development of infection structures, namely appressoria and penetration pegs. Exogenous dsRNA sprayed onto 1‐year‐old trees significantly reduced myrtle rust symptoms. Furthermore, we used comparative genomics to assess the wide‐scale amenability of dsRNA to control rust fungi. We sequenced genomes of six species of rust fungi, including three new families (Araucariomyceaceae, Phragmidiaceae, and Skierkaceae) and identified key genes of the RNAi pathway across 15 species in eight families of Pucciniales. Together, these findings indicate that dsRNA targeting essential genes has potential for broad‐use management of rust fungi across natural and agricultural systems. [ABSTRACT FROM AUTHOR]

There is no published information on the seed germination or seed storage physiology of Lophomyrtus bullata, Lophomyrtus obcordata, and Neomyrtus pedunculata. This lack of information is hampering conservation efforts of these critically endangered species. This study investigated the seed morphology, seed germination requirements, and long-term seed storage methods for all three species. The impact of desiccation, desiccation and freezing, as well as desiccation plus storage at 5 °C, −18 °C, and −196 °C on seed viability (germination) and seedling vigour was assessed. Fatty acid profiles were compared between L. obcordata and L. bullata. Variability in storage behaviour between the three species was investigated through differential scanning calorimetry (DSC) by comparing thermal properties of lipids. L. obcordata seed were desiccation-tolerant and viability was retained when desiccated seed was stored for 24 months at 5 °C. L. bullata seed was both desiccation- and freezing-sensitive, while N. pedunculata was desiccation-sensitive. DSC analysis revealed that lipid crystallisation in L. bullata occurred between −18 °C and −49 °C and between −23 °C and −52 °C in L. obcordata and N. pedunculata. It is postulated that the metastable lipid phase, which coincides with the conventional seed banking temperature (i.e., storing seeds at −20 ± 4 °C and 15 ± 3% RH), could cause the seeds to age more rapidly through lipid peroxidation. Seeds of L. bullata, L. obcordata and N. pedunculata are best stored outside of their lipid metastable temperature ranges. [ABSTRACT FROM AUTHOR]

The invasive rust Austropuccina psidii was detected in the Hawaiian Islands in 2005 and has become widely established throughout the archipelago in both native and introduced species of Myrtaceae. Initial predictions about the impacts of the fungus on native ʽōhiʽa lehua (Metrosideros polymorpha), a keystone native tree, have not materialized, but there is ongoing concern that introductions of new genotypes of the fungus could lead to widespread mortality with catastrophic effects on native ecosystems. By contrast, two recently emergent Ascomycete pathogens, Ceratocystis lukuohia (Ceratocystis wilt of 'ōhi'a) and C. huliohia (Ceratocystis canker of 'ōhi'a), collectively known to cause Rapid ʽŌhiʽa Death (ROD), are causing significant mortality in native forests on Hawaiʻi and Kauaʻi Islands, but pathways of spread are still incompletely understood. We used a network of passive environmental samplers for collecting windblown urediniospores of Austropuccina to evaluate the effectiveness of environmental monitoring to detect seasonal and landscape-scale differences in airborne propagules of this rust on Hawai'i Island. The samplers were also used to determine if windborn ambrosia beetle frass or spores of Ceratocystis can spread long distances. We found frequent detections and regional and seasonal differences in numbers of samplers that were positive for urediniospores of Austropuccinia, but little evidence of long-distance airborne dispersal of the ROD-causing fungi. The simple, inexpensive platform for sampling airborne fungal spores that we used may have value as a monitoring tool for detecting spread of airborne fungal pathogens, evaluating habitats for suitability for restoration efforts, and for detecting new pathogen introductions, particularly new Austropuccinia genotypes both in Hawaiʻi and other parts of the world. [ABSTRACT FROM AUTHOR]

The detection of kauri dieback and myrtle rust pathogens in Aotearoa|New Zealand prompted the government to fund research and engagement into what has been constructed both as a biosecurity risk and a threat to species of profound cultural significance. Researchers, iwi, public sector staff and community members are now working across projects and locations to build an understanding of these two plant pathogens and to develop protections for the trees they target. This paper combines interview material from two projects within Ngā Rakau Taketake's Postcolonial Biosecurity Possibilities remit to investigate the factors that enable and constrain plant pathogen research and practice. Actors in this space discuss the difficulty of working around gaps in basic research, a fragmented and competitive research sector, and expectations of a technological fix for a complex pathogen and its varied ecological relations. We argue that these accounts illustrate the ongoing effects of Aotearoa's neoliberal turn, which continues to shape knowledge production and, in turn, what it is to be a researcher in Aotearoa. While the effects of these reforms have been well documented in relation to higher education and other spheres, their impact on the sciences has received less scrutiny. Foregrounding the views of those involved in kauri dieback and myrtle rust highlights the everyday manifestations and material environmental consequences of a pervasively neoliberalised research landscape. [ABSTRACT FROM AUTHOR]

Managing unwanted pests and diseases is a growing concern. Recent shifts in state‐led biosecurity policy have seen a movement towards 'shared responsibility' between government, industry and communities. We use social practice theory to show how materials, skills and meanings come together to shape how people understand the spread of myrtle rust (Austropuccinia psidii), an unwanted disease in Aotearoa New Zealand. We show how 'shared responsibility' has emerged in the shift from a government‐led incursion response to myrtle rust, to passive disease reporting using iNaturalist. We offer a reflective aid to help biosecurity practitioners better consider participatory practices for plant health. [ABSTRACT FROM AUTHOR]

Austropuccinia psidii, the fungus causing myrtle rust, was detected in Western Australia for the first time in June 2022. Few Western Australian plant species have been screened for response to the pathogen. Melaleuca thyoides, Melaleuca marginata and Melaleuca leucadendra grown from seeds sourced from Western Australian populations were all highly susceptible to an isolate of the pathogen from eastern Australia. [ABSTRACT FROM AUTHOR]

Myrtaceae are a large family of woody plants, including hundreds that are currently under threat from the global spread of a fungal pathogen, Austropuccinia psidii (G.Winter) Beenken, which causes myrtle rust. A reference genome for the Australian native rainforest tree Rhodamnia argentea Benth. (malletwood) was assembled from Oxford Nanopore Technologies (ONT) long-reads, 10x Genomics Chromium linked-reads, and Hi-C data (N50 = 32.3 Mbp and BUSCO completeness 98.0%) with 99.0% of the 347 Mbp assembly anchored to 11 chromosomes (2n = 22). The R. argentea genome will inform conservation efforts for Myrtaceae species threatened by myrtle rust, against which it shows variable resistance. We observed contamination in the sequencing data and further investigation revealed an arthropod source. This study emphasises the importance of checking sequencing data for contamination, especially when working with non-model organisms. It also enhances our understanding of a tree that faces conservation challenges, contributing to broader biodiversity initiatives., (© The Author(s) 2024. Published by Oxford University Press on behalf of Society for Molecular Biology and Evolution.)

Austropuccinia psidii is a biotrophic fungus that causes myrtle rust. First described in Brazil, it has since spread to become a globally important pathogen that infects more than 480 myrtaceous species. One of the most important commercial crops affected by A. psidii is eucalypt, a widely grown forestry tree. The A. psidii–Eucalyptus spp. interaction is poorly understood, but pathogenesis is likely driven by pathogen-secreted effector molecules. Here, we identified and characterized a total of 255 virulence effector candidates using a genome assembly of A. psidii strain MF-1, which was recovered from Eucalyptus grandis in Brazil. We show that the expression of seven effector candidate genes is modulated by cell wax from leaves sourced from resistant and susceptible hosts. Two effector candidates with different subcellular localization predictions, and with specific gene expression profiles, were transiently expressed with GFP-fusions in Nicotiana benthamiana leaves. Interestingly, we observed the accumulation of an effector candidate, Ap28303, which was upregulated under cell wax from rust susceptible E. grandis and described as a peptidase inhibitor I9 domain-containing protein in the nucleus. This was in accordance with in silico analyses. Few studies have characterized nuclear effectors. Our findings open new perspectives on the study of A. psidii–Eucalyptus interactions by providing a potential entry point to understand how the pathogen manipulates its hosts in modulating physiology, structure, or function with effector proteins.

Neomyrtus is a New Zealand endemic monotypic genus that has been assigned to the Myrtaceae tribe Myrteae. Previous phylogenetic studies using the five genetic markers ITS, ETS, matK, psbA-trnH, and rpl16 have placed the single species Neomyrtus pedunculata in a clade with the New Zealand endemic Lophomyrtus (subtribe Ugninae), comprising the two species L. bullata and L. obcordata. Examination of the single herbarium voucher (OTA 57310) representing the plant material from which the DNA for the five phylogenetic markers was obtained revealed that it had been misidentified as Neomyrtus pedunculata and that it actually belongs to Lophomyrtus obcordata. We conducted a reanalysis of previously published data with new sequences from Neomyrtus and also undertook an analysis of 85 kbp of plastid protein coding genes from available Myrteae plastid genomes. These new phylogenetic analyses place Neomyrtus as sister to the New Caledonian endemic genus Myrtastrum, and the two species of Lophomyrtus form a clade that is sister to the Australian endemic Lenwebbia. Neomyrtus and Lophomyrtus are not closely related within the context of the tribe. This change to the understanding of Myrteae phylogeny is discussed in terms of available morphological character data and the biogeography of the tribe. Myrtastrum is currently treated as incertae sedis at subtribal rank, but along with Neomyrtus could be considered as representing a new subtribe as our analyses suggest they are not part of any of the clades hitherto recognised as subtribes. [ABSTRACT FROM AUTHOR]

Abstract Plants use a wide array of secondary metabolites including terpenes as defense against herbivore and pathogen attack, which can be constitutively expressed or induced. Here, we investigated aspects of the chemical and molecular basis of resistance against the exotic rust fungus Austropuccinia psidii in Melaleuca quinquenervia, with a focus on terpenes. Foliar terpenes of resistant and susceptible plants were quantified, and we assessed whether chemotypic variation contributed to resistance to infection by A. psidii. We found that chemotypes did not contribute to the resistance and susceptibility of M. quinquenervia. However, in one of the chemotypes (Chemotype 2), susceptible plants showed higher concentrations of several terpenes including α‐pinene, limonene, 1,8‐cineole, and viridiflorol compared with resistant plants. Transcriptome profiling of these plants showed that several TPS genes were strongly induced in response to infection by A. psidii. Functional characterization of these TPS showed them to be mono‐ and sesquiterpene synthases producing compounds including 1,8‐cineole, β‐caryophyllene, viridiflorol and nerolidol. The expression of these TPS genes correlated with metabolite data in a susceptible plant. These results suggest the complexity of resistance mechanism regulated by M. quinquenervia and that modulation of terpenes may be one of the components that contribute to resistance against A. psidii.

In 2010, the fungal plant pathogen that causes Myrtle rust, Austropuccinia psidii, which is native to South America, was first detected in Australia and has since had significant impacts on several Australian Myrtaceae species. Despite this, our understanding of the role secondary metabolites play in plant susceptibility to A. psidii is limited. This study aimed to determine: (1) whether secondary metabolite (phenolics, terpenes) production is induced after A. psidii inoculation and if so, (2) how their production relates to A. psidii susceptibility. To test these aims, we selected seven Myrtaceae species that have a wide range of within-species variability in their susceptibility to A. psidii. We found that five of the study species significantly increased either their phenolic or sesquiterpene production post-inoculation suggesting their pre-inoculation secondary metabolite levels were not sufficient to combat A. psidii infection. The two species (Angophora costata and Corymbia citriodora) that did not increase their secondary metabolite production post-inoculation tended to have the greatest pre-inoculation production levels amongst the species. Interestingly, across all species, monoterpenes were the only secondary metabolite found to reduce plant susceptibility to A. psidii. This study contributes to our limited understanding of the role that secondary metabolites play in plant susceptibility to A. psidii. In light of these findings, future research should aim to identify biomarkers (e.g. individual chemical compounds) that confer resistance to A. psidii, so that individuals with these biomarkers can be utilised in commercial and conservation projects. [ABSTRACT FROM AUTHOR]

Globalisation has resulted in the spread of infectious plant diseases to new regions and host species and the novel disease caused by myrtle rust poses a global threat to naïve hosts in the Myrtaceae family of plants. This study uses a focal species, Tristaniopsis exiliflora, to explore the climatic and microclimatic preference of the myrtle rust disease (Austropuccinia psidii). Populations of T. exiliflora were sampled across the species distribution in Far North Queensland, Australia, modelling A. psidii severity as a function of macro- and micro-environmental variables. Disease severity was found to increase with annual precipitation and foliage projective cover, and decrease with maximum temperature and valley confinement. A subsampled population found that individuals with lower canopy heights experienced more severe disease. Our results suggest that, in tropical environments with seasonal rainfall, A. psidii virulence is reduced when mean annual rainfall is less than 1500 mm and virulence is substantially reduced when maximum temperatures exceed 32 °C. The climatic drivers identified in this study align with optimal in vitro conditions for A. psidii germination and development. This suggests that climatic conditions are regulating myrtle rust in natural ecosystems at a broader scale, and that increased conservation efforts should focus on species with narrow climatic distributions and highly susceptible regions such as the Wet Tropics World Heritage Area. [ABSTRACT FROM AUTHOR]

Aims: The Myrtaceae is a woody family that plays an important role in forest ecosystems globally. The recent spread of myrtle rust, caused by a fungal pathogen (Austropuccinia psidii), from its native South America into New Zealand (NZ), highlights the need to quantify the ecological importance of Myrtaceae in NZ woody ecosystems. Location: New Zealand. Methods: Using NZ nationwide forest and shrubland inventory data, collected from 2009 to 2014, we quantified the ecological importance of Myrtaceae based on its richness and abundance relative to co-occurring woody families. We then explored how climate and forest stand structure affect Myrtaceae importance in general and by tribe and growth form. Finally, we compared functional traits associated with plant growth and reproductive strategies with other dominant woody families and determined Myrtaceae's contributions to community-weighted mean (CWM) trait values. Results: Myrtaceae occurred in 74% of the study plots and its importance value was the second highest across the woody families. It was the only one in which climbers substantially contributed to the importance value (17%). Greater Myrtaceae importance values were associated with warmer and more mesic climates and early forest successional stages. Climate associations were similar within tribes and growth forms, whereas forest structure effects varied. Myrtaceae was functionally distinct from most co-occurring woody families. Contributions to CWM wood density, maximum height, and specific leaf area values were significantly greater than expected from its importance value. Conclusions: Myrtaceae is the second most ecologically important woody family in NZ woody ecosystems. The family has a distinctive functional trait spectrum associated with high wood density and tall stature, ensuring large and enduring carbon stocks. There will potentially be large and deleterious outcomes in forest ecosystems if taxon-specific pathogens, such as Austropuccinia psidii, spread and significantly reduce Myrtaceae importance. [ABSTRACT FROM AUTHOR]

Myrtle rust is a serious fungal disease caused by Austropuccinia psidii affecting a number of Myrtaceae species in New Zealand and elsewhere. Control with fungicides or biologicals provides a mechanism to reduce the build-up of inoculum in the short-term while other strategies are being developed or deployed for long-term management. This study evaluated the efficacy of fungicides for control of myrtle rust under controlled conditions and identified adjuvants that would promote spreading of fungicidal active ingredients across the leaf surface. The spread of fungicide on detached M. excelsa leaves was assessed by applying three different adjuvants in combination with seven fungicides. Subsequently, M. excelsa plants were treated with three fungicides/mixes, (azoxystrobin + epoxiconazole, triademinol or a natural tea-extract) at a single rate followed by inoculation with A. psidii urediniospores on day 0, 7, 14 or 21 days after spraying. The response to infection in M. excelsa plants based on different inoculation timings at days 0, 7 and 21 significantly differed among fungicide treatments. The fungicide azoxystrobin + epoxiconazole was the most effective with infections significantly lower on the adaxial leaf surface than abaxial, despite good surface coverage of fungicide being achieved on both leaf surfaces. There were significant differences among fungicides based on the proportion of infected leaves on M. excelsa plants. Day 21 post-spray inoculation indicated a significant interaction between inoculation time and fungicide on leaf disease ratings. However, this was not the case at either 28 or 35 days post-inoculation. This research contributes to fungicide options for myrtle rust control in New Zealand. [ABSTRACT FROM AUTHOR]

There is no published information on the seed germination or seed storage physiology of Lophomyrtus bullata, Lophomyrtus obcordata, and Neomyrtus pedunculata. This lack of information is hampering conservation efforts of these critically endangered species. This study investigated the seed morphology, seed germination requirements, and long-term seed storage methods for all three species. The impact of desiccation, desiccation and freezing, as well as desiccation plus storage at 5 °C, −18 °C, and −196 °C on seed viability (germination) and seedling vigour was assessed. Fatty acid profiles were compared between L. obcordata and L. bullata. Variability in storage behaviour between the three species was investigated through differential scanning calorimetry (DSC) by comparing thermal properties of lipids. L. obcordata seed were desiccation-tolerant and viability was retained when desiccated seed was stored for 24 months at 5 °C. L. bullata seed was both desiccation- and freezing-sensitive, while N. pedunculata was desiccation-sensitive. DSC analysis revealed that lipid crystallisation in L. bullata occurred between −18 °C and −49 °C and between −23 °C and −52 °C in L. obcordata and N. pedunculata. It is postulated that the metastable lipid phase, which coincides with the conventional seed banking temperature (i.e., storing seeds at −20 ± 4 °C and 15 ± 3% RH), could cause the seeds to age more rapidly through lipid peroxidation. Seeds of L. bullata, L. obcordata and N. pedunculata are best stored outside of their lipid metastable temperature ranges.

Current forest biosecurity systems and processes employed in many countries are, in large, constructs of Western principles, values and science knowledge that have been introduced and integrated internationally. They are often devoid of knowledge, and of the values and principles, held by indigenous people, even those who have an intimate and enduring relationship with their forests. Indigenous people are also often overlooked in policy and decision-making processes, yet are often most affected by biosecurity pests and pathogens that impact native plant species that they may rely on for sustenance, cultural or spiritual purposes. By adopting an inclusive approach, scientists and indigenous people can achieve more comprehensive and robust biosecurity outcomes through a shared diversity of knowledge and at the same time serves to elevate and recognise the importance of indigenous knowledge. A co-innovation approach can also result in more widespread adoption of tools or practices by end-users including indigenous people. Understanding New Zealand Māori and their unique knowledge base can help improve forest biosecurity systems and practices, as can discussions of barriers that can and have prevented adoption of inclusiveness. Here we outline key principles behind indigenous engagement, specifically the need to develop enduring relationships.

Plants use a wide array of secondary metabolites including terpenes as defense against herbivore and pathogen attack, which can be constitutively expressed or induced. Here, we investigated aspects of the chemical and molecular basis of resistance against the exotic rust fungus Austropuccinia psidii in Melaleuca quinquenervia, with a focus on terpenes. Foliar terpenes of resistant and susceptible plants were quantified, and we assessed whether chemotypic variation contributed to resistance to infection by A. psidii. We found that chemotypes did not contribute to the resistance and susceptibility of M. quinquenervia. However, in one of the chemotypes (Chemotype 2), susceptible plants showed higher concentrations of several terpenes including α‐pinene, limonene, 1,8‐cineole, and viridiflorol compared with resistant plants. Transcriptome profiling of these plants showed that several TPS genes were strongly induced in response to infection by A. psidii. Functional characterization of these TPS showed them to be mono‐ and sesquiterpene synthases producing compounds including 1,8‐cineole, β‐caryophyllene, viridiflorol and nerolidol. The expression of these TPS genes correlated with metabolite data in a susceptible plant. These results suggest the complexity of resistance mechanism regulated by M. quinquenervia and that modulation of terpenes may be one of the components that contribute to resistance against A. psidii. [ABSTRACT FROM AUTHOR]

Syzygium maire is an endemic tree in New Zealand and classified as critically endangered. The in situ populations of this species are further threatened by the incursion of myrtle rust. The biology and ecology of S. maire have not been well documented and limited information on seed development, effective germination and seed storage behaviour of S. maire are hampering ex situ conservation and restoration. In this study, we investigated fruit and seed development on S. maire populations growing at four sites and in different seasons, and used short-term seed storage protocols to investigate the storage potential of harvested seeds. Fruit development took 8–11 months with three of the four identified stages occurring during the warmer spring and summer months. Embryos were found to be viable from stage two, but seedlings from final stage embryos were more robust. The moisture content of the fruit pulp varied between populations and within populations between seasons, but embryo moisture content remained more constant. S. maire seeds have high germinability when removed from the fruit pulp, and removal from the pulp is essential for germination. Seeds in fruits stored hydrated at 5°C remained viable for up to 12 weeks, although some germination was observed from eight weeks. This paper identifies optimal time for seed collection to ensure high quality seed for propagation and restoration while the short term storage provides an opportunity for further research into long term seed conservation through cryopreservation. [ABSTRACT FROM AUTHOR]

Austropuccinia psidii, originating in South America, is a globally invasive fungal plant pathogen that causes rust disease on Myrtaceae. Several biotypes are recognized, with the most widely distributed pandemic biotype spreading throughout the Asia-Pacific and Oceania regions over the last decade. Austropuccinia psidii has a broad host range with more than 480 myrtaceous species. Since first detected in Australia in 2010, the pathogen has caused the near extinction of at least three species and negatively affected commercial production of several Myrtaceae. To enable molecular and evolutionary studies into A. psidii pathogenicity, we assembled a highly contiguous genome for the pandemic biotype. With an estimated haploid genome size of just over 1Gb (gigabases), it is the largest assembled fungal genome to date. The genome has undergone massive expansion via distinct transposable element (TE) bursts. Over 90% of the genome is covered by TEs predominantly belonging to the Gypsy superfamily. These TE bursts have likely been followed by deamination events of methylated cytosines to silence the repetitive elements. This in turn led to the depletion of CpG sites in TEs and a very low overall GC content of 33.8%. Compared to other Pucciniales, the intergenic distances are increased by an order of magnitude indicating a general insertion of TEs between genes. Overall, we show how TEs shaped the genome evolution of A. psidii and provide a greatly needed resource for strategic approaches to combat disease spread. [ABSTRACT FROM AUTHOR]

The current threat of myrtle rust (Austropuccinia psidii) to New Zealand Myrtaceae, including a number of indigenous and socio-economically important species, requires that ex situ conservation is used to complement in situ populations. New Zealand's Myrtaceae have received little attention in terms of ex situ conservation. In this study, we assessed the integrated ex situ conservation strategies for selected New Zealand Myrtaceae. We particularly investigated seed banking options by assessing seed desiccation tolerance, in vitro culture, pollen cryopreservation and zygotic embryo cryopreservation of the recalcitrant Syzygium maire. A desiccation trial was conducted on six Myrtaceae species: Lophomyrtus bullata, L. obcordata, Metrosideros diffusa, M. umbellata, M. bartlettii and Syzygium maire. S. maire seeds and embryos showed extreme sensitivity to desiccation confirming its recalcitrant behaviour. The seeds of the other species were desiccation tolerant i.e. orthodox. Zygotic embryos of S. maire were successfully cryopreserved using an encapsulation-dehydration technique. Pollen cryopreservation was successful for M. excelsa following desiccation to about 5% moisture content, rapid freezing and rapid thawing. For M. bartlettii, one of the most endangered and a nationally critical Myrtaceae species in New Zealand, we tested the efficacy of hand pollination in producing viable seeds. Our assessment confirmed that one of the M. bartlettii trees at Otari is self-incompatible, and successful hand pollination using pollen obtained from different genotypes growing in the gardens at the University of Auckland resulted in seed production with c. 20% germination. Tissue culture protocols were successfully developed for selected Myrtaceae. In addition, photoautotrophic micropropagation techniques were developed for the first time for L. scoparium. This paper highlights the importance of holistic conservation strategies to ensure future access to New Zealand's unique Myrtaceae germplasm as a key component of long-term management response to the threat posed by A. psidii. [ABSTRACT FROM AUTHOR]

The global spread of invasive plant pathogens is increasing, putting natural forests and ecosystem services under threat. Spatial data can quantify range non‐overlap between invasive pathogens and their hosts to identify existing and potentially restorable refugia to enable 'escape' from the pathogen.In 2017, myrtle rust Austropuccinia psidii was detected in New Zealand. New Zealand has 27 native woody and liana species in the plant family susceptible to the disease (Myrtaceae), many of which are ecosystem dominants and economically important. Spatial methods were used to compare the current New Zealand distribution of myrtle rust with the modelled distributions of its potential native hosts. To guide management and set priorities for conservation of at‐risk species, areas of potential refugia where a Myrtaceae species is predicted to occur outside the pathogen range were identified under two myrtle rust distribution scenarios.Myrtle rust will thrive in New Zealand's warmer regions. Many native Myrtaceae are distributed within this area, but several species occur extensively outside the core range of the disease. Species distributed in cooler southern regions will be best placed to persist in refugia.Myrtaceae species with specific habitat requirements and narrow geographical ranges in warmer (northern) areas are likely to require ex situ or active in situ management. Even widely distributed species will benefit from the restoration of suitable habitat that supports multiple species outside the myrtle rust range.Synthesis and applications. Spatial data can be used to identify refugia and restoration opportunities, and thus inform landscape‐level management responses to invasive pathogens. This approach can guide decisions over where to implement in situ (e.g. fungicide spraying) versus ex situ (e.g. seed banking, botanic gardens) management efforts. [ABSTRACT FROM AUTHOR]

The use of sentinel or expatriate plants is a growing concept for risk assessment in plant biosecurity. This approach involves ascertaining the presence and impact of pests and pathogens on plants foreign to a given location but planted in international botanic gardens or arboreta. The data obtained provide information on the potential pest status of these pests and pathogens, as invasive alien species (IAS), to plant species in their native or indigenous range. Assessment of the biosecurity threat from IAS for indigenous plants not found within the geographic distribution of these pests and pathogens is challenging, however, as they may be relatively taxonomically distinct from plants found in the distribution of the IAS and can be in different climates and environments. We examine the sentinel/expatriate concept in relation to risk assessment for myrtle rust (Austropuccinia psidii) on New Zealand Myrtaceae on these plants found in botanic gardens and arboreta outside New Zealand. Between September 2017 and September 2018, we identified and then contacted 65 botanic gardens or arboreta that putatively had New Zealand Myrtaceae and were within the known distribution of myrtle rust. We asked for information on the presence of New Zealand Myrtaceae species in their collections and whether these plants were infected by myrtle rust. Sixteen gardens/arboreta responded; most were in Australia or the United States. Only one of these gardens provided information that was useful for biosecurity risk assessment for myrtle rust on New Zealand Myrtaceae. The results are discussed in the context of plant biosecurity risk assessment and the broader sentinel/expatriate plant concept. [ABSTRACT FROM AUTHOR]

Austropuccinia psidii is a fungal plant pathogen that infects species within the Myrtaceae, causing the disease myrtle rust. Myrtle rust is causing declines in populations within natural and managed ecosystems and is expected to result in species extinctions. Despite this, variation in response to A. psidii exist within some species, from complete susceptibility to resistance that prevents or limits infection by the pathogen. Untargeted metabolomics using Ultra Performance Liquid Chromatography with Ion Mobility followed by analysis using MetaboAnalyst 3.0, was used to explore the chemical defence profiles of resistant, hypersensitive and susceptible phenotypes within Melaleuca quinquenervia during the early stages of A. psidii infection. We were able to identify three separate pools of secondary metabolites: (i) metabolites classified structurally as flavonoids that were naturally higher in the leaves of resistant individuals prior to infection, (ii) organoheterocyclic and carbohydrate-related metabolites that varied with the level of host resistance post-infection, and (iii) metabolites from the terpenoid pathways that were responsive to disease progression regardless of resistance phenotype suggesting that these play a minimal role in disease resistance during the early stages of colonization of this species. Based on the classes of these secondary metabolites, our results provide an improved understanding of key pathways that could be linked more generally to rust resistance with particular application within Melaleuca.

It is challenging to sequence and assemble genomes of obligate plant pathogens and microorganisms because of limited amounts of DNA, comparatively large genomes and high numbers of repeat regions. We sequenced the 1.2 gigabase genome of an obligate rust fungus, Austropuccinia psidii, the cause of rust on Myrtaceae, with a Chromium 10X library. This technology has mostly been applied for single-cell sequencing in immunological studies of mammals. We compared scaffolds of a genome assembled from the Chromium library with one assembled from combined paired-end and mate-pair libraries, sequenced with Illumina HiSeq. Chromium 10X provided a superior assembly, in terms of number of scaffolds, N50 and number of genes recovered. It required less DNA than other methods and was sequenced and assembled at a lower cost. Chromium sequencing could provide a solution to sequence and assemble genomes of obligate plant pathogens where the amount of available DNA is a limiting factor.

Corymbia citriodora subsp. variegata (CCV) is an economically and ecologically important timber species, native to eastern Australia. It is highly susceptible to Quambalaria pitereka, a coevolved endemic pathogen, and Austropuccinia psidii, an exotic invasive pathogen. Genes associated with resistance to Q. pitereka are specific and uncorrelated with the genes associated with resistance to A. psidii, suggesting different resistance mechanisms to each pathogen, possibly associated with leaf phenotypic traits. This study examined leaf chemical and anatomical differences in CCV between uninoculated plants and those inoculated with Q. pitereka and A. psidii. The results demonstrate that the pathogens induce different responses in CCV. Plants inoculated with A. psidii exhibited chemical and anatomical changes that were not observed in uninoculated controls and Q. pitereka-inoculated plants, such as deposition of polyphenols and tannins in upper/lower epidermis, variation in the proportion of monoterpenes, steroids, monounsaturated hydrocarbons and long chain hydrocarbons and higher leaf toughness. In contrast, CCV response to Q. pitereka altered the distribution of polyphenols and tannins in the leaves and possible accumulation of these compounds and lignin in necrotic areas. These findings provide a better understanding of factors underlying CCV responses to coevolved and exotic pathogens and add insights into plant-pathogen interactions. [ABSTRACT FROM AUTHOR]

Key MessageA resistantE. grandisgenotype showed a constitutive overexpression of genes related to resistance to myrtle rust caused byA. psidii. Abstract Myrtle rust caused by Austropuccinia psidii is considered one of the most important fungal diseases affecting Eucalyptus spp. plantations in Brazil. Although the selection and planting of resistant eucalypt genotypes have been the major strategies to manage the disease in Brazil, the molecular mechanisms involved in resistance are still unclear. In this study, we evaluated the gene expression profile of two contrasting Eucalyptus grandis genotypes in resistance level to rust by RNA-Seq. The two genotypes showed a very different background gene expression level even without A. psidii infection. The resistant genotype had a constitutive overexpression of a large number of protein-coding genes compared to the susceptible genotype. These genes were mainly associated with signal transduction, photosynthesis, regulation and response to salicylic acid (SA), and protein kinase leucine-rich receptors (PK-LRR). PK-LRR and SA mediated disease resistance are well known to be effective against obligate biotroph pathogens, such as A. psidii. In addition, at 24 h after infection, the susceptible genotype was able to activate some response, however, several resistance-related proteins had their expression level reduced with A. psidii infection. Here, we present the first analysis of E. grandis genotypes transcriptomes infected by A. psidii and it reveals a constitutive overexpression of several resistance-related genes in the resistant genotype compared to the susceptible one. Our findings have the potential to be used as candidate molecular markers for resistance to myrtle rust. [ABSTRACT FROM AUTHOR]

Myrtle rust is a fungal disease that has spread rapidly across the globe, arriving in Australia in 2010. The tree species Rhodomyrtus psidioides is nearly extinct in the wild as a result of the disease, leading to potential disruption of ecosystem function. Many other Myrtaceae may also be threatened and unprecedented impacts of the disease are predicted. [ABSTRACT FROM AUTHOR]

Austropuccinia psidii is a rust fungus that has expanded its known geographic distribution and host range on Myrtaceae. Invasions by rust fungi are often caused by asexual urediniospores that give rise to populations with low genotypic diversity. Recently it was shown that basidiospores, the gametic spores of A. psidii, were able to infect species of Myrtaceae under controlled conditions. The present study tested the hypothesis that sexual reproduction occurs through infection of Myrtaceae by basidiospores of A. psidii in recently invasive populations from New Zealand and South Africa. We provided three lines of evidence to test this hypothesis: i) presence of a sexual stage, ii) high genotypic diversity within an invasive population, and iii) no genetic linkage between microsatellite markers in multilocus genotypes. Our results provide evidence that invasions of A. psidii are caused by both urediniospores that spread clonal genotypes, and teliospores that produce recombinant basidiospores, which infect Myrtaceae. We reject the hypothesis that field infections of A. psidii are only caused by asexual urediniospores, and support that sexual reproduction occurs in invasive populations and may accelerate adaptation to environmental change. [ABSTRACT FROM AUTHOR]

Myrtle rust (caused by Austropuccinia psidii) affects more than 500 known host species in the Myrtaceae family. Three different modelling approaches (CLIMEX, MaxEnt and Multi‐Model Framework) were used to project the habitat suitability for myrtle rust at both global and local scales. Current data on the global occurrence of myrtle rust were collected from online literature and expert solicitation. Long‐term averages of climate data (1960–1990) were sourced from WorldClim and CliMond websites. Recent reports of myrtle rust in New Zealand were used for validation of model outputs but not in model training and testing. The model outputs were combined into a consensus model to identify localities projected to be suitable for myrtle rust according to two or three models (hotspots). In addition to the locations where the pathogen is currently present, all models successfully projected independent occurrence data in New Zealand suitable for establishment of the pathogen. Climate suitability for the pathogen was primarily related to temperature followed by rainfall in MaxEnt and the CLIMEX model. The results confirmed the optimum temperature range of this pathogen in the literature (15–25 °C). Additional analysis of the precipitation variables indicated that excessive rain (more than 2000 mm in warmest quarter of the year) combined with high temperatures (>30 °C) constrain pathogen establishment. The results of the current study can be useful for countries such as New Zealand, China, South Africa and Singapore where the pathogen has not fully spread or established. [ABSTRACT FROM AUTHOR]

This study compared the susceptibility of E. pilularis progenies (from Brazilian populations) to myrtle rust under controlled and field conditions in Brazil. High levels of resistance were observed under both controlled (96% resistant individuals) and field (97% resistant individuals) conditions, despite the optimum climatic conditions for disease development. Assessment of field susceptibility was more accurate at 14 months compared to 2–6 months. Individual heritability was higher under controlled conditions (h2a = 0.81) compared to field conditions (h2a = 0.17), indicating the former to be a more reliable method for testing susceptibility. Eucalyptus pilularis is rust tolerant while heritability is higher under controlled conditions compared to field conditions. [ABSTRACT FROM AUTHOR]

The myrtle rust pathogen, Austropuccinia psidii, was recently detected in New Zealand and Singapore. We used microsatellite markers to identify the strain of A. psidii that caused these incursions. Our results show that the pandemic strain of the pathogen caused outbreaks in both New Zealand and Singapore. [ABSTRACT FROM AUTHOR]

BACKGROUND: The response to infection of Austropuccinia psidii in resistant (CLR‐383) and susceptible (CLR‐384) Eucalyptus grandis clones, exposed to herbicide drift of carfentrazone‐ethyl, glyphosate and a mixture of these two herbicides, was evaluated at microscopic and physiological levels. RESULTS: Plants of the two clones showed symptoms of phytotoxicity caused by herbicide drift. However, net CO2 assimilation rate, height and shoot dry matter were lower in CLR‐384 than in CLR‐383. At the ultrastructure level, the leaves of both clones exposed to the herbicides showed thylakoid disorganization and accumulation of starch grains in the chloroplasts. Only plants of CLR‐384 were infected by A. psidii, but when exposed to herbicide drift, rust severity was lower than in control plants. Six days after inoculation (dai), plants of this clone exposed to the herbicides had smaller uredinia than control plants. At 12 dai, non‐herbicide treated plants showed normal uredinia, containing abundant urediniospores. By contrast, plants exposed to the herbicides were less colonized by the fungus, and the uredinia were smaller with reduced production of urediniospores, which were sometimes not even detected. CONCLUSION: Glyphosate and carfentrazone‐ethyl herbicide drift reduce infection and uredinial formation of A. psidii and to some extent induce basal resistance in a susceptible clone of E. grandis. © 2018 Society of Chemical Industry In this study, we noted that eucalyptus plants previously submitted to glyphosate and carfentrazone‐ethyl herbicide drift showed malformed uredinias, without urediniospores of A. psidii, reducing the rust severity. [ABSTRACT FROM AUTHOR]

This study aimed to characterise the life cycle of Austropuccinia psidii , the causal agent of myrtle rust, in guava cv. Paluma and to determine how this pathogen affects gas exchange in diseased leaves. The pathogen formed appressoria on ordinary epidermal cells and intercellular hyphae and intracellular branched lobe-shaped haustoria in parenchyma cells. In the stem, hyphae grew in the cortical region and crossed between tracheary cells, reaching the medullary region. In the leaf, hyphae colonised the intercellular spaces of the main vein and mesophyll and the substomatal chamber. Colonisation of the substomatal chamber by A. psidii changed the stomatal dynamics and leaf gas exchange. The stomatal response to light was slower and had a smaller amplitude in diseased guava leaves. Consequently, impaired stomatal movement induced by A. psidii is an additional factor changing the performance of plants under abiotic stress. • Histopathology of the myrtle rust are described for Austropuccinia psidii biotype associated with guava. • Colonisation of the substomatal chamber by A. psidii changes the stomatal dynamics and leaf gas exchange. • The stomatal response to light is slower and have a smaller amplitude in diseased guava leaves. • The pathogen can impair not only photosynthesis but also water transport, which is driven by transpiration. [ABSTRACT FROM AUTHOR]

Background and objectives: The global forest economy is threatened by eucalypt pathogens which are often latent or cryptic species that escape common quarantine and detection methods. Plantation forestry using eucalypts is of considerable importance to Paraguay, but knowledge regarding the pests and diseases affecting these plantations is limited. This study identified fungal diseases present in these plantations. Materials and Methods: We surveyed eucalypt plantations in four provinces in Paraguay and collected material from diseased trees for identification of the causal agents. The samples were analyzed using a combination of morphological and molecular methods. Results: Diseases encountered included Botryosphaeria stem canker, Calonectria leaf blight, Chrysoporthe stem canker, myrtle/eucalypt rust, Coniella leaf spot, heartwood rot and Teratosphaeria stem canker. Contrary to expectations, the causal agent of Teratosphaeria stem canker was identified as Teratosphaeria zuluensis (M.J. Wingf., Crous & T.A. Cout.) M.J. Wingf. & Crous and not Teratosphaeria gauchensis (M.-N. Cortinas, Crous & M.J. Wingf.) M.J. Wingf. & Crous, that is commonly documented for the South American region. Conclusions: This study updates the knowledge on forest fungal pathogens in Paraguayan eucalypt plantations and is the first report of T. zuluensis in Paraguay and in South America.

Summary: Myrtle rust, caused by the fungus Austropuccinia psidii, infects a wide range of host species within the Myrtaceae family worldwide. Since its first report in 2013 from New Caledonia, the extent of the host range, geographical distribution and genetic diversity of A. psidii in this territory have been unknown. This study reports 67 new host species distributed in 13 different Myrtaceae genera, including five new genera. The pathogen was found in various types of plant communities, where Myrtaceae species are the dominant or codominant species, as well as in several nurseries. It is now considered a significant threat to the biodiversity of ecosystems and the Myrtaceae‐related economy. A 3‐year disease monitoring trial with 35 cultivated Myrtaceae species showed variations in disease severity at the species and individual scales. This suggests that some level of genetic resistance to myrtle rust may possibly exist among the endemic Myrtaceae of New Caledonia. A population genetic investigation revealed that only one single genotype of A. psidii occurs across its entire host range in New Caledonia. Therefore, it is essential to carry out population genetic surveillance to identify the appearance of mutations or the introduction of potentially more virulent genotypes of A. psidii. The outcomes from this study will assist with the ongoing management of the disease in New Caledonia. [ABSTRACT FROM AUTHOR]