Telial Hosts Research Articles

First report of Gymnotelium blasdaleanum causing Saskatoon serviceberry rust in Canada.

Saskatoon serviceberry (Amelanchier alnifolia) is a tall shrub native to the western regions of North America. In British Columbia, serviceberries are a resource for Indigenous communities, used in cooking and for medicinal purposes (Turner et al. 1990). The Saskatoon serviceberry is popular for ornamental and food purposes, with increasing demand for commercial production in British Columbia. (FLNR, 2003). In June 2023 leaf and fruit samples displaying signs of a rust fungus were collected from three ornamental Saskatoon serviceberry shrubs on the University of British Columbia's campus in Vancouver, BC (49°15'35.0"N 123°15'05.6"W). Morphological characteristics were taken from six leaves and berries. Infected leaf tissue was misshapen due to the development of aecia on the abaxial side of the leaves. Approximately 80% of the berries were enveloped in aecia, while infected leaf tissue constituted only around 5% across all three shrubs. Aecia were aecidioid (aecidium type) 0.25 to 0.35mm in diameter, hypophylous and, fructicolous. Peridial cells had a rhomboid shape measuring 21-29 × 18-23 μm (average dimension 25 × 20 μm, n = 30). Aeciospores were globoid with yellowish walls, verrucose and the dimensions ranged from 16-24 × 12-15 μm, (average dimensions 19 ×15 μm, n = 30) (Fig. x). These morphological features fit well with description of Gymnotelium blasdaleanum (Dietel & Holw.) Arthur (= Gymnosporangium libocedri (Henn.) F. Kern) (Arthur 1934). Judging from U.S. National Fungal Databases (https://fungi.ars.usda.gov/) G. blasdaleanum has never been reported in Canada, thus this discovery represents the first report of G. blasdaleanum in the country, specifically in the province of British Columbia. G. blasdaleanum is a hetero-demicyclic rust fungus with a broad aecial host range which includes several Rosaceous genera such as Amelanchier, Crataegus, Cydonia, Malus, Pyrus, and Sorbus (Farr & Rossman 2019). The telial host range is limited to California incense cedar (Calocedrus decurrens) and was not observed on nearby trees, some located within one kilometer of the serviceberries. To confirm morphological identification, DNA was extracted from infected leaves and fruits from all three plants using a modified protocol (Russell et al., 2010). The D1/D2 region was amplified using primers LR6 and 2Rust1R (Beenken, et al., 2012). A BLASTn search of all three sequences revealed 99.52 to 99.62% identity to available sequence in GenBank from Gymnotelium blasdaleanum (AF522168). Newly generated sequences were submitted to the GenBank under accession numbers OR567878, OR568568, and OR654105. Specimens from three Saskatoon serviceberry plants were provided to the UBC herbarium (Beaty Biodiversity Museum) and deposited in their fungarium (F35820). Infected fruits undergo deformation and premature dropping, posing a significant threat to ornamental and fruit production varieties of serviceberries (EPPO, 2006). The spread and establishment of the G. blasdaleanum is highly dependent on the presence of C. decurrens because of its limited range. However, California incense cedar is planted outside its natural range in suitable environments for G. blasdaleanum to thrive such as southern BC allowing the rust pathogen to spread to Canada. To prevent potential spread into other agricultural industries, particularly the 256-acre pear cultivation, continued planting of C. decurrens in British Columbia should be closely monitored. (BC MFLNRO, 2003).

Aecial and Telial Host Specificity of Puccinia coronata var. coronata, a Eurasian Crown Rust Fungus of Two Highly Invasive Wetland Species in North America.

The Eurasian crown rust fungus Puccinia coronata var. coronata (Pcc) was recently reported in North America and is widespread across the Midwest and Northeast United States. Pcc is a close relative of major pathogens of oats, barley, and turfgrasses. It infects two highly invasive wetland plants, glossy buckthorn (Frangula alnus) and reed canarygrass (Phalaris arundinacea), and could be useful as an augmentative biological control agent. We conducted large greenhouse trials to assess the host specificity of Pcc and determine any threat to cultivated cereals, turfgrasses, or native North American species. A total of 1,830 accessions of cereal crop species and 783 accessions of 110 other gramineous species were evaluated. Young plants were first inoculated with a composite uredinial inoculum derived from aecia. Accessions showing sporulation were further tested with pure urediniospore isolates. Sixteen potential aecial hosts in the families Rhamnaceae and Elaeagnaceae were tested for susceptibility through inoculation with germinating teliospores. Thirteen grass species within five genera in the tribe Poeae (Apera, Calamagrostis, Lamarckia, Phalaris, and Puccinellia) and four species in Rhamnaceae (Frangula alnus, F. californica, F. caroliniana, and Rhamnus lanceolata) were found to be susceptible to Pcc, with some species native to North America. All assessed crop species and turfgrasses were resistant. Limited sporulation, however, was observed on some resistant species within Poeae and four other tribes: Brachypodieae, Bromeae, Meliceae, and Triticeae. Among these species are oats, barley, and Brachypodium distachyon, suggesting the possible use of Pcc in studies of nonhost resistance.

First report of Melampsora ferrinii (pucciniales) on Babylon willow (Salix babylonica) in Iran

As an agroforestry resource willow species (Salix spp.) becoming increasingly important in the protection of riverbanks, recovery of floodable lands, soil bioremediation, biomass production, and wicker furniture manufacture, Babylon willow (Salix babylonica) is widely planted all over the world and is found throughout Iran as part of the rural landscape and is mostly planted for ornamental or bioremediation purposes. Rust fungi in the genus Melampsora usually cause disease on Salix species. Identification of Melampsora species is often complicated because there are few differences in spore morphology and little publicly available comparative sequence data. Willow trees in Iran have been reported to be infected by 15 Melampsora species; however, most of these records are based on morphological characterization. During surveillance activities carried out in June 2007, a rust species was detected on isolated Babylon willow trees in an area in Northern Iran. Both the rust fungus and the host plant were identified on the basis of morphological features and DNA sequencing. Based on a combination of morphology, large subunit (LSU) rDNA sequencing and phylogenetic analyses, our rust specimen was identified as Melampsora ferrinii, which is newly reported from Iran on Salix babylonica. Melampsora ferrinii was originally described from the Americas and this is the first time this rust has been observed on its telial host, Babylon willow, in Asia. The documentation of the rust fungus was performed using both scanning electron microscopy (SEM) and light microscopy. Additionally, an identification key for Melampsora species reported on Salix spp. in Iran is included.

First report of a rust fungus (Puccinia sp.) infecting lemongrass in Minnesota.

In July 2021 and July - Oct. 2022, in a community garden near Mankato, Minnesota, rust disease was observed on lemongrass (Cymbopogon citriatus). In 2022, all 20 plants in the garden plot were infected. Lemongrass is used in some Asian cuisines and for tea or medicine. It is not hardy in Minnesota but is grown in gardens and outdoors in small-scale production. Uredinia were cinnamon-brown on the abaxial surface of leaf blades. Pustules were small (0.2 - 0.5 x .01 - .05 mm) and numerous, causing large necrotic lesions and leaf dieback (Fig. 1A). Severity ranged from 5 - 50% leaf loss. Urediniospores were finely echinulate, slightly ovular (22-25 x 20-23 μm), thick-walled (2.5-4 μm), with 3-4 roughly equatorial, sometimes scattered germ pores (Fig 1B; 1C). Clavate paraphyses were abundant. Other spore types were not observed. The pycnidia of a mycoparasitic fungus were present within the uredinia. The specimen was submitted to the Arthur Fungarium at Purdue University (PUR N24011). Primers ITS1rustF10d (Barnes and Szabo, 2007) and ITSRu1 (Rioux et al., 2015) were used to generate amplicons for the rust fungus, and ITS4 and ITSF+ (White, 1990) for the mycoparasite. Amplicons were sequenced on an Oxford Nanopore MinIon with R9 flow cells following manufacturer instructions. Reads (PRJNA802078) were filtered for quality (> Q13) and length (> 200 bp), mapped to reference sequences, aligned, and separated based on similarity. Consensus sequences were generated for the amplicons of the rust fungus and of two other fungi. BLASTn searches of the ITS sequences, OM442990 and OM442991, identified an Alternaria sp. (99.8% match (597/598) with MT548677) and Sphaerellopsis filum (syn. Darluca filum; 98.3% (529/538 bp) match with EF600974), a common rust mycoparasite. A BLASTn search of the rust fungal ITS sequence (OM442989) yielded 98.9% (549/555) and 98.6% (633/642) match with MT955206 and MT955207, respectively, both Puccinia cesatii on Bothriochloa ischaemum. The third closest match is P. cymbopogonis on C. citriatus (97.1% (595/613) with KY764115). Urediniospore morphology is consistent with that of P. cesatii (Cummins, 1971). Available evidence suggests the fungus is P. cesatii or a closely related species. Puccinia cesatii has been reported infecting Cymbopogon spp. (Stevenson et al., 1926; Dhar and Rekha, 1984), but lemongrass is not generally considered a host-possibly due to confusion of P. cesatii with P. cymbopogonis, a closely related rust pathogen of lemongrass that is morphologically very similar to P. cesatii. P. cymbopogonis has not been reported in the U.S. Rust diseases of lemongrass have been reported in three states: Hawaii (Gardner, 1985), California (Koike and Molinar, 1999), and Florida (Ploetz et al., 2014). In each case, the rust was identified as Puccinia nakanishikii. Urediniospores of P. nakanishikii are larger (26-36 μm long) (Cummins, 1971) and the ITS2 has no significant sequence similarity. P. cesatii is widespread in Eurasia, the southwest U.S., and Mexico (Cummins, 1971). Cummins lists three genera closely related to Cymbopogon as telial hosts of P. cesatii: Bothriochloa, Capillipedium, and Dicanthium. He lists nine rust fungi that infect Cymbopogon but does not list P. cesatii. Of these nine species, only P. cymbopogonis is morphologically similar. Further research is needed to investigate the potential impact of rust fungi on lemongrass production and to elucidate phylogenetic relationships of rust fungi infecting lemongrass.

Pest categorisation of Coleosporium asterum, C. montanum and C. solidaginis.

The EFSA Plant Health Panel performed a pest categorisation of Coleosporium asterum (Dietel) Sydow & P. Sydow, Coleosporium montanum (Arthur & F. Kern) and Coleosporium solidaginis (Schwein.) Thüm, three basidiomycete fungi belonging to the family Coleosporiaceae, causing rust diseases on Pinus spp. (aecial hosts) and on Asteraceae (telial hosts). Coleosporium asterum was described on Aster spp. in Japan and has been reported from China, Korea, France and Portugal. Coleosporium montanum is native to North America, has been introduced to Asia and has been reported from Austria on Symphyotrichum spp. Coleosporium solidaginis has been reported on Solidago spp. from North America, Asia and Europe (Switzerland and Germany). There is a key uncertainty about these reported distributions, due to the until recently accepted synonymy between these fungi and the lack of molecular studies. The pathogens are not listed in Annex II of Commission Implementing Regulation (EU) 2019/2072, an implementing act of Regulation (EU) 2016/2031, or in any emergency plant health legislation. There are no reports of interceptions of C. asterum, C. montanum or C. solidaginis in the EU. The pathogens can further enter into, establish in and spread within the EU via host plants for planting, other than seeds and host plant parts (e.g. cut flowers, foliage, branches), other than fruits. Entry into and spread within the EU may also occur by natural means. Host availability and climate suitability in the EU are favourable for the establishment of the pathogens in areas where host plants in the Asteraceae and Pinaceae co-exist. Impacts can be expected on both aecial and telial hosts. Phytosanitary measures are available to reduce the risk of further introduction and spread of the three pathogens in the EU. Coleosporium asterum, C. montanum and C. solidaginis satisfy the criteria that are within the remit of EFSA to assess for these species to be regarded as Union quarantine pests, but a key uncertainty exists about their EU distribution.

Comparative transcriptome analysis of juniper branches infected by Gymnosporangium spp. highlights their different infection strategies associated with cytokinins

BackgroundGymnosporangium asiaticum and G. yamadae can share Juniperus chinensis as the telial host, but the symptoms are completely different. The infection of G. yamadae causes the enlargement of the phloem and cortex of young branches as a gall, but not for G. asiaticum, suggesting that different molecular interaction mechanisms exist the two Gymnosporangium species with junipers.ResultsComparative transcriptome analysis was performed to investigate genes regulation of juniper in responses to the infections of G. asiaticum and G. yamadae at different stages. Functional enrichment analysis showed that genes related to transport, catabolism and transcription pathways were up-regulated, while genes related to energy metabolism and photosynthesis were down-regulated in juniper branch tissues after infection with G. asiaticum and G. yamadae. The transcript profiling of G. yamadae-induced gall tissues revealed that more genes involved in photosynthesis, sugar metabolism, plant hormones and defense-related pathways were up-regulated in the vigorous development stage of gall compared to the initial stage, and were eventually repressed overall. Furthermore, the concentration of cytokinins (CKs) in the galls tissue and the telia of G. yamadae was significantly higher than in healthy branch tissues of juniper. As well, tRNA-isopentenyltransferase (tRNA-IPT) was identified in G. yamadae with highly expression levels during the gall development stages.ConclusionsIn general, our study provided new insights into the host-specific mechanisms by which G. asiaticum and G. yamadae differentially utilize CKs and specific adaptations on juniper during their co-evolution.

Rust on Hosta longipes caused by Puccinia oncospora in Korea

Hosta longipes (Liliaceae), widely distributed throughout Korea, China, Japan, and eastern Russia, is one of the most popular ornamental perennials in public and private gardens. In Korea, this species has long been used as a traditional medicine for the treatment of coughs, phlegm, burns, swelling and asthma (Kim et al., 2014), and its young leaves are also consumed as a salad vegetable. In June 2016, rust disease was observed on H. longipes plants growing naturally around a stream at Mount Gongjaksan in Hongcheon-gun, Korea (Fig. 1). The disease incidence rate was c. 10%. Symptoms appeared as yellowish, round, chlorotic spots on the upper surface of the infected leaves (Fig. 2) and yellow to orange-coloured aecia on the corresponding lower surface and petiole (Fig. 3). After the first findings, the same disease was observed in 2017, 2019 and 2020. Herbarium specimens of infected material were deposited in the Korea University Herbarium (Accession Nos. KUS-F29182, F29810, F30967, and F31685). Leaves affected by the rust infection were examined under a dissecting microscope (M205C; Leica, Germany), a DIC microscope (Axio Imager 2; Carl Zeiss, Germany), and a scanning electron microscope (S-4800+EDS; Hitachi, Japan). Spermogonia were mostly epiphyllous but rarely hypophyllous, densely grouped, pale brown, and subepidermal. Aecia were hypophyllous, often densely grouped, yellow, cupulate with peridia, and 196–300 μm in diameter (Fig. 4). Aeciospores were hyaline, globose to subglobose, angular, and (20.2-)22.0-24.9(-27.4) × (17.0-)19.6-22.5(-24.2) μm (mean 23.4 × 21.0 μm) (Fig. 5). Aeciospore wall was densely verrucose and 0.6-1.6 μm (mean 1.0 μm) in thickness (Fig. 6). Uredinial and telial stages were not observed. These morphological characteristics were consistent with those of Puccinia oncospora (Ji et al., 2022). To confirm the morphology-based identification, genomic DNA was extracted from four specimens using a MagListo 5M plant Genomic DNA Extraction Kit (Bioneer, Korea). Two ribosomal DNA regions were amplified: the internal transcribed spacer (ITS) with primers ITS5u and ITS4rust (Pfunder et al., 2001) and the large subunit (LSU) rDNA with primers LRust1R and LRust3 (Beenken et al., 2012). The resulting sequences were deposited in GenBank (Accession Nos. OQ061206-9 for ITS and OQ073721-4 for LSU) and compared to other reference sequences using BLASTn. The ITS sequences of Korean specimens were identical to those of P. oncospora ex Trillium kamtschaticum and Phalaris arundinacea for ITS (MW404821-5) and LSU sequences (MW404981-5). In maximum-likelihood phylogenetic trees for ITS (Fig. 7A) and LSU (Fig. 7B) sequences, the Korean samples were grouped with the reference sequences of P. oncospora with high bootstrap supporting values of 93% in ITS and 96% in LSU. Puccinia oncospora is a recently described rust species that is so far only known from China, where it completes its life cycle by forming an aecial stage on Trillium kamtschaticum (Melanthiaceae, previously Liliaceae) and a telial stage on Phalaris arundinacea (Poaceae; Ji et al., 2022). So far, three species of Puccinia have been recorded on Hosta longipes, namely, P. funkiae, P. hemerocallidis, and P. majanthemi (Hiratsuka & Sato, 1951; Farr & Rossman, 2022). Also, a species complex P. sessilis was considered parasitic on H. longipes (Hiratsuka & Sato, 1951), but it is phylogenetically and morphologically distinguishable from P. oncospora. To our knowledge, this is the first record of rust disease on Hosta longipes and this rust pathogen in Korea. As there have been no records of rust on P. arundinacea, a telial host plant of P. oncospora, in Korea, finding an alternative host for that rust is necessary to develop effective control measures. This work was supported by the National Academy of Agricultural Science grant (PJ0149560112020) from the Rural Development Administration, Korea.

Pest categorisation of Coleosporium phellodendri.

The EFSA Plant Health Panelperformed a pest categorisation of Coleosporium phellodendri Kom., a basidiomycete fungus belonging to the order Pucciniales, causing rust diseases on Pinus spp. (aecial host) and on Phellodendron spp. (telial host). C.phellodendri has been reported only from Asia (namely, China, Republic of Korea, Japan and Russia) and is not known to be present in the EU territory. The pathogen is not listed in Annex II of Commission Implementing Regulation (EU) 2019/2072, an implementing act of Regulation (EU) 2016/2031, or in any emergency plant health legislation. The pathogen could enter into, become established in, and spread within the EU territory via host plants for planting and host plant parts (e.g. foliage, branches) other than seeds and fruits, respectively. Spread within the EU territory may also occur by natural means if Phellodendron spp. were present. Availability of the Pinus spp. and climate suitability factors occurring in the EU are favourable for the establishment of the pathogen in areas where Phellodendron spp. are also present. Phytosanitary measures are available to prevent the introduction and spread of the pathogen in the EU. C.phellodendri does not satisfy all the criteria assessed by EFSA for consideration as a Union quarantine pest as no economic and environmental impact of this pathogen is expected without widespread presence of Phellodendron spp. in the EU.

Studies on European rust fungi, Pucciniales: molecular phylogeny, taxonomy, and nomenclature of miscellaneous genera and species in Pucciniastraceae and Coleosporiaceae

Using molecular phylogenetic analyses (ITS) and morphological data obtained from light and electron microscopy, some European and North American species and genera placed or formerly placed in the genus Pucciniastrum in the Coleosporiaceae and Pucciniastraceae (Pucciniales) were taxonomically revised. The ITS analyses confirmed recent familiar concepts based on less variable markers except for the genus Hyalopsora. The family Pucciniastraceae is characterized by Abietoideae (Abies, Tsuga) aecial hosts. Pucciniastrum is described as a genus that consists of host-alternating species forming aecia on needles of Abies hosts, with special features of aeciospore morphology, and Onagraceae telial hosts. Other genera in the Pucciniastraceae are Calyptospora, Melampsorella, and additional taxa, which are currently provisionally placed in Pucciniastrum, but must be revised in future studies. Pucciniastrum epilobii (s. lat.), the type species of Pucciniastraceae, represents at least two species with different life cycles and urediniospore characteristics and is lecto- and epitypified. The family Coleosporiaceae, characterized by Pinoideae (Pinus) and Piceoideae (Picea) aecial hosts, contains Rosaceae rusts from three well-supported clades represented by three genera, Thekopsora, Quasipucciniastrum, and Aculeastrum gen. nov. Aculeastrum is characterized by coarsely arcuate ostiolar peridial cells and infects Rubus spp. telial hosts. The following new taxonomic combinations are proposed: Calyptospora ornamentalis comb. nov., Quasipucciniastrum ochraceum comb. nov., Q. potentillae comb. nov, Aculeastrum americanum comb. nov., and A. arcticum comb. nov. The results are discussed with emphasis on future studies in Pucciniastrum and the P. epilobii complex and on nomenclatural changes necessary for rust fungi due to the Shenzhen Code.

Identification of eight Berberis species from the Yunnan-Guizhou plateau as aecial hosts for Puccinia striiformis f. sp. tritici, the wheat stripe rust pathogen

Puccinia striiformis Westend. f. sp. tritici Erikss. (Pst) infects wheat and causes stripe rust. The rust is heteroecious with wheat as the primary uredinial and telial host and barberry (Berberis spp.) as the alternate pycnial and aecial host. More than 40 Berberis species have been identified as alternate hosts for Pst, and most of these are Chinese Berberis species. However, little is known about Berberis species or their geographic distributions in the Yunnan-Guizhou plateau in southwestern China. The Yunnan-Guizhou plateau is considered to be an important and relatively independent region for the evolution of the wheat stripe rust pathogen in China because the entire disease cycle can be completed within the region. In this study, we conducted a survey of barberry plants in the Yunnan-Guizhou plateau and identified the eight Pst-susceptible Berberis species under controlled conditions, including B. julianae, B. tsienii, B. veitchii, B. wilsonae, B. wilsonae var. guhtzunica, B. franchetiana, B. lepidifolia and B. pruinosa. These species are reported here for the first time to serve as alternate hosts for the wheat stripe rust pathogen under controlled conditions.

Distribution of species of the genus Gymnosporangium (Pucciniales) in Uzbekistan

In this study, we analyzed distribution of species of the genus Gymnosporangium in the mountain regions of Uzbekistan, including the Western Tien Shan and Pamir-Alay. Four species of Gymnosporangium (G. confusum, G. sabinae, G. fusisporum, and G. turkestanicum) are reported for Uzbekistan. The telial hosts of these rust fungi are species of the genus Juniperus, while aecial hosts in Uzbekistan are representatives of the genera Cotoneaster, Crataegus, Sorbus, and Pyrus (all Rosaceae). It has been found that the distribution patterns of species of Gymnosporangium within mountain areas of Uzbekistan depend largely on distribution of juniper woodlands because representatives of the genus Juniperus as telial hosts play a major role in the life cycle of these fungi. In that regard, Gymnosporangium species have not yet been recorded in the Nuratau Nature Reserve despite other favorable conditions for these rust fungi in this territory.

Pest categorisation of Gymnosporangium spp. (non-EU).

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of Gymnosporangium spp. (non‐EU), a well‐defined and distinguishable group of fungal plant pathogens of the family Pucciniaceae affecting woody species. Many different Gymnosporangium species are recognised, of which at least 14 species are considered not to be native in the European Union. All the non‐EU Gymnosporangium species are not known to be present in the EU and are regulated in Council Directive 2000/29/EC (Annex IAI) as harmful organisms whose introduction into the EU is banned. Gymnosporangium spp. are biotrophic obligate plant pathogens. These rust fungi are heteroecious as they require Juniperus, Libocedrus, Callitropsis, Chamaecyparis or Cupressus (telial hosts) and rosaceous plants of subfamily Pomoideae (aecial hosts) to complete their life cycle. The pathogens could enter the EU via host plants for planting (including artificially dwarfed woody plants) and cut branches. They could establish in the EU, as climatic conditions are favourable and hosts are common. They would be able to spread following establishment by movement of host plants for planting and cut branches, as well as by natural dispersal. Should Gymnosporangium spp. (non‐EU) be introduced in the EU, impacts can be expected in orchards, ornamental trees and nurseries. On telial hosts, these pathogens cause galls on stems, twigs and branches, and fusiform swellings on stems. Foliar infections on aecial hosts may lead to severe defoliations. The main knowledge gap concerns the limited available information on the biology, distribution range and impact of several non‐EU Gymnosporangium spp. The criteria assessed by the Panel for consideration of Gymnosporangium spp. (non‐EU) as potential quarantine pests are met, while, for regulated non‐quarantine pests, the criterion on the pest presence in the EU is not met.

Pest categorisation of Cronartium spp. (non-EU).

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of Cronartium spp. (non‐EU), a well‐defined and distinguishable group of fungal pathogens of the family Cronartiaceae. There are at least 40 species described within the Cronartium genus, of which two are considered native to the EU (C. gentianeum and C. pini) and one has been introduced in the 19th century (C. ribicola) and is now widespread in the EU – these three species are thus not part of this pest categorisation. In addition, the non‐EU C. harknessii, C. kurilense and C. sahoanum were already dealt with in a previous pest categorisation. All the non‐EU Cronartium species are not known to be present in the EU and are regulated in Council Directive 2000/29/EC (Annex IAI) as harmful organisms whose introduction into the EU is banned. Cronartium spp. are biotrophic obligate plant pathogens. Many of the North American Cronartium species alternate between the aecial host Pinus spp. and telial hosts of various dicotyledonous plants. C. conigenum, C. orientale, C. quercuum and C. strobilinum have different Quercus spp. as their telial hosts. C. orientale and C. quercuum also infect Castanea spp. and Castanopsis spp. The pathogens could enter the EU via host plants for planting and cut flowers and branches. Non‐EU Cronartium spp. could establish in the EU, as climatic conditions are favourable to many of them and Pinus and Quercus spp. are common. The pathogens would be able to spread following establishment by movement of host plants, as well as natural spread. Should non‐EU Cronartium spp. be introduced in the EU, impacts can be expected on pine, oak and chestnut woodlands, plantations, ornamental trees and nurseries. The Cronartium species present in North America cause important tree diseases. Symptoms on Pinus spp. differ between Cronartium spp., but include galls, cankers, dieback of branches and stems, deformity, tree and cone death. The main knowledge gap concerns the limited available information on (sub)tropical Cronartium spp. The criteria assessed by the Panel for consideration of Cronartium spp. (non‐EU) as potential quarantine pests are met, while, for regulated non‐quarantine pests, the criterion on the pest presence in the EU is not met.

Pest categorisation of Melampsora medusae.

Following a request from the European Commission, the EFSA Plant Health Panel performed a pest categorisation of Melampsora medusae, a well‐defined and distinguishable fungal species of the family Melampsoraceae. The pathogen is regulated in Annex IAI of Council Directive 2000/29/EC as a harmful organism whose introduction into the EU is banned. M. medusae is a heteroecious rust fungus with Populus spp. as primary telial hosts and various conifers (Larix, Pinus, Pseudotsuga, Abies, Picea and Tsuga spp.) as secondary aecial hosts. M. medusae is native to North America and has spread to South America, Africa, Asia, Oceania, as well as the EU, where M. medusae f. sp. deltoidae has been reported with a restricted distribution and low impacts from Belgium, south‐west France and southern Portugal. The pest could spread to other EU countries, via dissemination of spores, movement of host plants for planting and cut branches. Climate is assumed not to be a limiting factor for the establishment of the pathogen in the EU. M. medusae is the most widespread and important Melampsora rust in North America. In western Canada, extensive damage has been reported to conifers and Populus spp. in nurseries and plantations as well as in woodlands. M. medusae is damaging in both Australia and New Zealand. The pest could have economic and environmental impacts in the EU if aggressive isolates of M. medusae were introduced into the EU. Import prohibition of host plants for planting is an available measure to reduce the risk of further introductions. Some resistant Populus cultivars are available. Moreover, increasing the genetic diversity of poplar plantations can prevent disease impacts. The main uncertainty concerns the factors explaining the low pathogenicity of the populations of M. medusae present in the EU. The criteria assessed by the Panel for consideration as a potential quarantine pest are met (the pest is present, but with a restricted distribution, and is officially under control). Given that plants for planting are not the main pathway of spread, not all criteria for consideration as a regulated non‐quarantine pest are met.

Pest categorisation of Chrysomyxaarctostaphyli.

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of Chrysomyxa arctostaphyli, a well‐defined and distinguishable fungal species of the family Coleosporiaceae. The pathogen is regulated in Council Directive 2000/29/EC (Annex IAI) as a harmful organism whose introduction into the EU is banned. C. arctostaphyli is native to North America and is the causal agent of spruce broom rust. C. arctostaphyli is a heteroecious rust with a 2‐year life cycle alternating between the aecial host Picea spp. and the telial host Arctostaphylos spp. The main reported aecial host is P. engelmannii, but also P. abies, P. pungens, P. sitchensis, P. glauca, P. mariana and P. rubens (as well as Picea as a genus) are reported as hosts. The fungus is not known to occur in the EU but could enter via host plants for planting and cut branches. It could establish in the EU, as hosts are present and climatic conditions are favourable. The extent of overlap between the ranges of the telial and aecial hosts is greater in the EU than in North America. The pathogen would be able to spread following establishment by dissemination of spores and human movement of infected host plants. Should the pathogen be introduced in the EU, impacts can be expected in spruce woodland, plantations and on ornamental spruce trees, leading to reduced tree growth and associated ecosystem service provision. The main uncertainty concerns the level of susceptibility of P. abies and P. sitchensis under European conditions. The criteria assessed by the Panel for consideration as a potential quarantine pest are met. As the pest is not present in the EU, not all criteria for consideration as a regulated non‐quarantine pest are met.

FIRST REPORT OF LEAF RUST CAUSED BY MELAMPSORA MAGNUSIANA ON POPULUS ALBA IN ITALY

In October 2016, Melampsora spp. hypophyllous uredinia (0.3-0.5 mm in diameter) were observed on leaves of Populus alba L. clones cultivated in Casale Monferrato at CREA-PLF (Piedmont, northern Italy). Morphological observations and DNA sequencing of the Internal Transcribed Spacer (ITS) region were performed to identify the fungus at the species level. Urediniospores were yellowish, obovate, verrucose and on average 23.3 x 18.8 µm (wall 1.22-2.44 µm thick). DNA was extracted from urediniospores with the Quiagen Plant DNeasy Mini-kit following manufacturer’s instructions. The ITS region was amplified and sequenced with taxon selective primers ITS1-F and ITS4-B (Gardes and Bruns, 1993). Sequences were deposited in GenBank (accession Nos. KY364897, KY364898) and compared with those of known Melampsora species using the NCBI GenBank nucleotide BLAST search. Based on morphological features of uredinia and urediniospores and DNA sequences the fungus was identified, according to Vialle et al. (2011), as Melampsora magnusiana G.H. Wagner, belonging to M. populnea complex and associated with P. alba, P. tremula L. and P. x canescens (Aiton) Sm. telial hosts. The identification of this Melampsora species was also supported by the presence of its known aecial hosts Chelidonium majus L. and Corydalis spp. in the neighborhood of the sampling site (Picco, 2010). Telia were not observed. Disease symptoms consisting of chlorotic spots were reproduced on the abaxial surface of ten leaves cut from five P. x canescens, belonging to the same clone, artificially inoculated by spraying a spore suspension of the fungus (105 spores ml-1 ). Uredinia were observed ten days after inoculation. Non-inoculated leaves remained symptomless. To our knowledge, this is the first report of M. magnusiana on P. alba in Italy, although it was observed in some European countries (Pei and McCraken, 2005) on both Populus spp. and aecial hosts.

First Report of Puccinia coronata var. coronata sensu stricto Infecting Alder Buckthorn in the United States

Field symptoms, host distribution, pathogen morphology, and phylogenetic analyses clearly demonstrated that the rust fungus infecting alder buckthorn in Connecticut is Puccinia coronata var. coronata sensu stricto. To our knowledge, this is the first report and confirmation of P. coronata var. coronata s.s. in the United States. Additional collections from purported aecial and telial hosts of P. coronata var. coronata s.s. are necessary to determine its host range, geographic distribution, and incidence within the United States and elsewhere in North America.

Inferring phylogeny and speciation of Gymnosporangium species, and their coevolution with host plants.

Gymnosporangium species (Pucciniaceae, Pucciniales) cause serious diseases and significant economic losses to apple cultivars. Most of the reported species are heteroecious and complete their life cycles on two different plant hosts belonging to two unrelated genera, i.e. Juniperus and Malus. However, the phylogenetic relationships among Gymnosporangium species and the evolutionary history of Gymnosporangium on its aecial and telial hosts were still undetermined. In this study, we recognized species based on rDNA sequence data by using coalescent method of generalized mixed Yule-coalescent (GMYC) and Poisson Tree Processes (PTP) models. The evolutionary relationships of Gymnosporangium species and their hosts were investigated by comparing the cophylogenetic analyses of Gymnosporangium species with Malus species and Juniperus species, respectively. The concordant results of GMYC and PTP analyses recognized 14 species including 12 known species and two undescribed species. In addition, host alternations of 10 Gymnosporangium species were uncovered by linking the derived sequences between their aecial and telial stages. This study revealed the evolutionary process of Gymnosporangium species, and clarified that the aecial hosts played more important roles than telial hosts in the speciation of Gymnosporangium species. Host switch, losses, duplication and failure to divergence all contributed to the speciation of Gymnosporangium species.

Phenolic profiles of two Melampyrum species differing in susceptibility to Cronartium rust

Cronartium flaccidum is an important pathogen in boreal forestry where it causes pine stem rust. The hemiparasite Melampyrum sylvaticum serves as a telial host for this heteroecious fungus while the congeneric M. pratense is highly resistant. We hypothesized that the variation in susceptibility is due to differences in the composition of secondary phenolic compounds in host plant tissues. To test this hypothesis, phenolic compounds of leaf extracts taken from both species of Melampyrum were analyzed with HPLC. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used for data processing. PCA indicated difference between the species, with the first two components explaining more than 70 % of the total variance of data that was separated into two distinct groups in a scatter plot. Two clusters, formed by the two species, were also suggested by HCA. Phenolic acids (such as chlorogenic acid), flavanones and apigenin flavonoids dominated the profiles of rust-resistant M. pratense, while kaempferol and luteolin flavonoids occurred in high relative concentrations in rust-susceptible M. sylvaticum. Our results suggest that phenolics may contribute to resistance or susceptibility of Melampyrum to Cronartium rusts as one factor. Future studies on the mode of action of phenolics in this interaction are thus warranted.

Tranzschelia in the Americas revisited: two new species and notes on the Tranzschelia thalictri complex

Two new species of Tranzschelia (Pucciniales) are described from the Americas. Tranzschelia pseudofusca is a microcyclic species on Anemone spp. (Ranunculaceae) with North American distribution. T. mexicana on Prunus salicifolia (Rosaceae) is found in Colombia, Ecuador and Mexico. It is assumed that T. mexicana is a macrocyclic host-alternating species. T. thalictri, a holarctic microcyclic species, has variable morphology and probably is an aggregate of related species. Specimens are documented with scanning electron microscopy (ESEM) and light microscopy including a simple new technique to illuminate urediniospore germ pores. Results are discussed with respect to similar species, distribution and life-cycle characters. A key for American species on telial hosts is provided.