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Puccinia psidii infection on eucalypt. (a) Urediniospores on leaves and shoots. (b) Urediniospore pustules. (c) Apical death. (d) Resistance reactions: (1) susceptible, (2) resistant and (3) hypersensitive response.
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Puccinia psidii causes a rust disease on a broad range of hosts in the Myrtaceae and Heteropyxidaceae. It is native to South America where
it can cause severe disease in eucalypt plantations and other introduced Myrtaceae. The pathogen has recently expanded its
geographical range to Hawaii, increasing concerns about the potential for an incursion i...
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Citations
... In addition, the myrtle rust disease caused by Austropuccinia psidii (syn. Puccinia psidii) (Uredinales, Pucciniaceae) is considered an important quarantine threat (Glen et al. 2007;Fensham et al. 2020), which became notorious when it started to infect various species of the Myrtaceae (Coutinho et al. 1998;Glen et al. 2007;Carnegie et al. 2010;Morin et al. 2012;Roux et al. 2013). Recently, Italian provenances of M. communis were shown to be highly susceptible to Austropuccinia psidii, highlighting a significant threat to myrtle cultivation if the pathogen were accidentally introduced to the Mediterranean (Paap et al. 2023). ...
... In addition, the myrtle rust disease caused by Austropuccinia psidii (syn. Puccinia psidii) (Uredinales, Pucciniaceae) is considered an important quarantine threat (Glen et al. 2007;Fensham et al. 2020), which became notorious when it started to infect various species of the Myrtaceae (Coutinho et al. 1998;Glen et al. 2007;Carnegie et al. 2010;Morin et al. 2012;Roux et al. 2013). Recently, Italian provenances of M. communis were shown to be highly susceptible to Austropuccinia psidii, highlighting a significant threat to myrtle cultivation if the pathogen were accidentally introduced to the Mediterranean (Paap et al. 2023). ...
Pestalotioid fungi were isolated in pure culture from symptomatic plants of Callistemon laevis, C. viminalis, Luma apiculata (marketed as "Myrtus luma"), Myrtus communis sub-sp. tarentina, and M. communis var. microphylla (M. communis 'Microphylla'), showing twig canker, dieback and defoliation. The isolates were identified to species by ITS, tef1 and tub2 sequences, which revealed the presence of six species of Neopestalotiopsis (N. camelliae-oleiferae, N. hispanica, N. iberica, N. rosae, N. rosicola, and N. zakeelii) and one species of Pestalotiopsis (P. biciliata). While most species were isolated only once or twice, the majority of isolates belonged to N. rosae (13) and N. hispanica (8). Pathoge-nicity was investigated by pathogenicity tests on all hosts, which confirmed the patho-genicity of all Neopestalotiopsis species on at least some of the hosts tested, while P. bi-ciliata did not cause any disease symptoms. Neopestalotiopsis hispanica and N. rosae caused symptoms in all hosts of the present study, while the other Neopestalotiopsis species tested showed no symptoms on Luma apiculata.
... In recent decades the rust fungus Austropuccinia psidii (Beenken 2017) has gained infamous familiarity due to its ability to cause severe infections on an unusually wide range of host plants in family Myrtaceae (Joffily 1944, Kawanishi 2009, Marlatt and Kimbrough 1979, Rayachhetry et al. 2001, Uchida 2006, Hennen et al. 2005, Carnegie & Pegg, 2018. Since its first description on guava (Psidium guajava) from Brazil as Puccinia psidii (Winter 1884), over 450 myrtaceous hosts have become known (Soewarto et al. 2019), threatening previously untouched ecosystems and leading to the decline, collapse, and likely extinction of individual endemic species in Hawaii, Australia, and New Zealand (Uchida et al. 2006, Glen et al. 2007, Pegg et al. 2017, Sommerville 2020, Fensham and Radford-Smith 2021. A first international alert focusing the guava rust fungus infecting Eucalyptus was issued by Dianese et al. (1983,1984) leading to the publication of the historical "Leaflet 45" (Australian Plant Quarantine 1985), organized by Dr. Sam Navaratnam. ...
In 1895 and 2001, rust fungi affecting Licania trees (Chrysobalanchaceae) in Brazil were described as Uredo licaniae by Hennings in the state of Goiás and as Phakopsora tomentosae by Ferreira et al. in the state of Amazonas, respectively. Recently, a Licania rust fungus collected close to the Amazonian type location sharing symptoms with the former two species was subjected to morphological examinations and molecular phylogenetic analyses using 28S nuc rDNA (ITS2-28S) and cytochrome c oxidase subunit III (CO3) gene sequences. Since the original type specimen of Ph. tomentosae is considered lost, we carefully reviewed the type description and questioned the identity of the telium, which justified the description of the fungus as a Phakopsora species. Furthermore, the additional revision of the type material described by Hennings revealed that Ph. tomentosae is a synonym of U. licaniae. Based on the morphological examinations, disease symptoms, and shared hosts, we concluded that the newly collected material is conspecific with U. licaniae. However, the phylogenetic analyses rejected allocation in Phakopsora and instead assigned the Licania rust fungus in a sister relationship with Austropuccinia psidii (Sphaerophragmiaceae), the causal agent of the globally invasive myrtle rust pathogen. We therefore favored a recombination of U. licaniae (syn. Ph. tomentosae) into Austropuccinia and proposed the new name Austropuccina licaniae for the second species now identified for this genus. The fungus shares conspicuous symptoms with A. psidii, causing often severe infections of growing leaves and shoots that lead to leaf necrosis, leaf shedding, and eventually to the dieback of entire shoots. In view of the very similar symptoms of its aggressively invasive sister species, we briefly discuss the current state of knowledge about A. licaniae and the potential risks, and the opportunity of its identification.
... Commonly known as myrtle rust, the disease caused by the fungus Austropuccinia psidii [2], basionym Puccinia psidii, affects plants in the Myrtaceae family. Native to South and Central America [3,4], invasive strains of the fungus have invaded new areas over the past two decades, having been reported in North America, parts of Asia, Australia, New Caledonia, South Africa and New Zealand [5]. Combined with the pathogen's wide host range within the Myrtaceae [6,7], the spread of A. psidii has been facilitated by the long-distance dispersal of urediniospores either via wind or anthropogenic movement of spores and infected plant material. ...
Myrtle rust is a very damaging disease, caused by the fungus Austropuccinia psidii, which has recently arrived in New Zealand and threatens the iconic tree species pōhutukawa (Metrosideros excelsa). Canopy-level hyperspectral and thermal images were taken repeatedly within a controlled environment, from 49 inoculated (MR treatment) and 26 uninoculated (control treatment) pōhutukawa plants. Measurements were taken prior to inoculation and six times post-inoculation over a 14-day period. Using indices extracted from these data, the objectives were to (i) identify the key thermal and narrow-band hyperspectral indices (NBHIs) associated with the pre-visual and early expression of myrtle rust and (ii) develop a classification model to detect the disease. The number of symptomatic plants increased rapidly from three plants at 3 days after inoculation (DAI) to all 49 MR plants at 8 DAI. NBHIs were most effective for pre-visual and early disease detection from 3 to 6 DAI, while thermal indices were more effective for detection of disease following symptom expression from 7 to 14 DAI. Using results compiled from an independent test dataset, model performance using the best thermal indices and NBHIs was excellent from 3 DAI to 6 DAI (F1 score 0.81–0.85; accuracy 73–80%) and outstanding from 7 to 14 DAI (F1 score 0.92–0.93; accuracy 89–91%).
... A. psidii is considered to have originated in South America (Glen et al., 2007), first described infecting P. guajava (guava) in Brazil (Winter, 1884). Austropuccinia psidii, popularly known as eucalyptus rust or myrtle rust, poses a major threat to the production and sustainability of eucalyptus forests globally. ...
Austropuccinia psidii, commonly known as eucalyptus rust, poses one of the major threats to eucalyptus forest production and sustainability worldwide. This fungus pathogen infects a wide range of hosts, primarily species within the Myrtaceae family, causing significant damage to the forestry industry and ecosystem. In light of this scenario, evaluating the genetic resistance of eucalyptus plants to rust becomes a crucial component in management and prevention strategies. This study investigates the phenotypic resistance of different clones of Eucalyptus dunnii and Eucalyptus grandis to A. psidii, a rust pathogen. The experiments were conducted in the nursery area located in Irati-PR, Brazil. Nine clones, totaling 180 plants, were inoculated with a suspension of A. psidii urediniospores and evaluated for disease severity using a resistance scale. Results revealed varying degrees of resistance among the clones, with E. dunnii clones demonstrating resistance, while E. grandis clones exhibited susceptibility and high susceptibility. There were significant variations both within and between species. These findings underscore the importance of genetic variability within and between species in selecting resistant clones for planting and disease management strategies. Further research is needed to explore broader genetic pools and genotype-environment interactions to enhance breeding and selection outcomes.
... Austropuccinia psidii is a biotrophic fungus [1] that causes rust disease in species of the Myrtaceae family, known as eucalypt rust, guava rust, 'ohi'a rust, or myrtle rust [2]. A. psidii is native to South America and was first reported in 1884 on infected native guava (Psidium guajava L.) [3], and on introduced eucalypts in 1912 in Brazil [4,5]. ...
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.
... Under changing environmental or within-host conditions, the activity of some endophytes may change to either beneficial or detrimental (Saikkonen et al., 1998;Slippers and Wingfield, 2007). Fungal endophytes of closely related introduced and native hosts often expand or shift hosts to include the newly encountered taxon (Slippers et al., 2005;Glen et al., 2007;Perez et al., 2012). Despite these host shifts or expansions, exotic (often cultivated) hosts tend to harbour lower fungal endophyte diversity compared to their native relatives (Saikkonen et al., 2000;Coleman-Derr et al., 2016). ...
Host identity and location help shape fungal endophyte assemblages in plants. Hosts act as uptake filters from the environment and closely related hosts in the same location may harbour similar assemblages. We assessed the influence of host identity and geographic location on endophytic fungal assemblages within the native African olive and cultivated European olive in South Africa using high throughput sequencing. As hypothesised, the two hosts were found to share many endophytic species, but alpha diversity was lower within the European olive. The two hosts had significantly dissimilar endophyte assemblages. Distance between sites positively correlated with endophyte assemblage dissimilarities, demonstrating a strong effect of the surrounding environment on endo-phyte assemblages. African olive individuals had highly connected endophyte assemblages, unlike those within the European olive. Microbiome sharing and disconnected assemblages may have negative impacts on the health of the cultivated host.
... However, the common guava (Psidium guajava) and Eucalyptus spp. are at more risk, as it causes severe infection in these plants [45][46][47]. A severe infection of P. psidii was reported in Brazil, which caused damage to various members of the family Myrtaceae [46,48,49]. ...
... A severe infection of P. psidii was reported in Brazil, which caused damage to various members of the family Myrtaceae [46,48,49]. Similarly, this fungus causes eucalyptus rust in Australia and poses a threat to the biodiversity in this country, as well as to the eucalyptus forest industry worldwide [45]. In 2017, based on a DNA-based molecular analysis of rust samples, the names were synonymized by Beenken in a new genus as Austropuccinia psidii [50]. ...
Puccinia, which comprises 4000 species, is the largest genus of rust fungi and one of the destructive plant pathogenic rust genera that are reported to infect both agricultural and nonagricultural plants with severe illnesses. The presence of bi-celled teliospores is one of the major features of these rust fungi that differentiated them from Uromyces, which is another largest genus of rust fungi. In the present study, an overview of the current knowledge on the general taxonomy and ecology of the rust genus Puccinia is presented. The status of the molecular identification of this genus along with updated species numbers and their current statuses in the 21st century are also presented, in addition to their threats to both agricultural and nonagricultural plants. Furthermore, a phylogenetic analysis based on ITS and LSU DNA sequence data available in GenBank and the published literature was performed to examine the intergeneric relationships of Puccinia. The obtained results revealed the worldwide distribution of Puccinia. Compared with other nations, a reasonable increase in research publications over the current century was demonstrated in Asian countries. The plant families Asteraceae and Poaceae were observed as the most infected in the 21st century. The phylogenetic studies of the LSU and ITS sequence data revealed the polyphyletic nature of Puccinia. In addition, the presences of too short, too lengthy, and incomplete sequences in the NCBI database demonstrate the need for extensive DNA-based analyses for a better understanding of the taxonomic placement of Puccinia.
... Winter) Beenken (basionym Puccinia psidii, Sphaerophragmiaceae, Pucciniales) has emerged as an important invasive plant pathogen, threatening Myrtaceae in planted and natural woody ecosystems globally (Coutinho et al. 1998;Carnegie et al. 2016;Roux et al. 2016;Beenken 2017). Originating in South America (Coutinho et al. 1998;Glen et al. 2007), the pathogen is the causal agent of a rust disease with common names including guava rust, eucalyptus rust, 'ōhi'a rust and myrtle rust. Austropuccinia psidii has a wide host range of over 480 species of Myrtaceae (Soewarto et al. 2019) and currently represents the major biosecurity threat for the Myrtaceae family. ...
Austropuccinia psidii , the causal agent of myrtle rust, has emerged as a significant threat to Myrtaceae in planted and natural woody ecosystems. The first detection of A. puccinia in South Africa was from severely infected ornamental Myrtus communis. This raised concern that M. communis , the sole Myrtaceae species native to Europe and an important component of vegetation in Mediterranean regions, could be threatened by the rust. In light of the potential threat to this unique species, seed was collected from 12 Italian provenances of M. communis , including mainland and island (Sardinia and Sicily) populations. We assessed the susceptibility of these provenances to both the pandemic and South African strains of A. psidii . In Colombia, where the pandemic strain of A. psidii is native, seedlings rapidly became infected by natural inoculum. In South Africa, a preliminary screening of seedlings by artificial inoculation with a single-uredinium isolate produced high levels of disease. Finally, plants of each of the 12 provenances were planted and monitored in Florence, Italy. To date, these showed no signs of disease, but will continue to be monitored. This study highlights the significant threat that both the pandemic and South African strains of A. puccinia pose to M. communis in Europe.
... These include certain pathogens that infect shoots or young tissues, such as some rust fungi. For example, the myrtle rust pathogen A. psidii, which is native to South America but has been introduced into many countries, has a wide host range and threatens both native forests and the global Eucalyptus industry (Glen et al. 2007). Numerous greenhouse studies using small plants have helped characterize the relative susceptibility of Eucalyptus spp. or important genotypes in advance of the pathogen's arrival (Roux et al. 2015). ...
Nonnative insects and pathogens pose major threats to forest ecosystems worldwide, greatly diminishing the ecosystem services trees provide. Given the high global diversity of arthropod and microbial species, their often unknown biological features or even identities, and their ease of accidental transport, there is an urgent need to better forecast the most likely species to cause damage. Several risk assessment approaches have been proposed or implemented to guide preventative measures. However, the underlying assumptions of each approach have rarely been explicitly identified or critically evaluated. We propose that evaluating the implicit assumptions, optimal usages, and advantages and limitations of each approach could help improve their combined utility. We consider four general categories: using prior pest status in native and previously invaded regions; evaluating statistical patterns of traits and gene sequences associated with a high impact; sentinel and other plantings to expose trees to insects and pathogens in native, nonnative, or experimental settings; and laboratory assays using detached plant parts or seedlings under controlled conditions. We evaluate how and under what conditions the assumptions of each approach are best met and propose methods for integrating multiple approaches to improve our forecasting ability and prevent losses from invasive pests.
... Responses to infection are species-specific, with symptoms ranging from mild to severe (Fernandez Winzer et al. 2019). Myrtle rust infects young growing tissues including flowers and fruits and, therefore it has a significant impact on seed production, while further suppressing regeneration through infection of seedlings (Glen et al. 2007;Beresford et al. 2020). A. psidii was observed for the first time in New Zealand during 2017 and has since spread throughout the North Island and northern South Island (Beresford et al. 2019;Toome-Heller et al. 2020;Schmid et al. 2021). ...
Syzygium maire (swamp maire) is an endemic New Zealand Myrtaceae tree species. Current threats to this species include habitat destruction, myrtle rust, declining remnant populations and low capacity for natural regeneration. Large-scale replanting for conservation/restoration initiatives would mitigate against these threats. However, there is limited information available on propagation of this species. In this study, we looked at sexual propagation using seed germination and asexual propagation using softwood cuttings. For seed germination, we examined the effect of seed pretreatments (intact fruit or de-pulped seed) and temperature settings (15/25°C or 20/30°C) to optimise germination. For softwood cutting propagation, we investigated the diameter of the cuttings (1–2mmor3–5 mm) and application of exogenous indole-3-butyric acid (IBA) (0, 1.5, 3.0, or 4.5 g L−1) on their efficacy of producing adventitious rooting. The most critical factor for seed germination was the removal of seed pulp. De-pulping the seeds shortened the mean time to germination and positively affected the germination percentage, regardless of the incubation temperature. Germination percentage of ≥94.5% was achieved in seeds sown without pulp. Propagation by softwood cutting of 1–2 mm in diameter was possible without IBA treatment (63.3% of cuttings rooted), but the application of 1.5 g L−1 IBA increased the rooting percentage (to 75%), thereby inducing the production of a higher number of roots. Seed germination and softwood cutting were effective strategies to propagate S. maire. The findings of this research contribute to the knowledge of propagation and restoration of S. maire populations.
