Gymnosporangium Species Research Articles

Occurrence of rust disease Caused by Gymnosporangium pleoporum on Cotoneaster acutifolius in China.

Species of Gymnosporangium are major pathogenic rust fungi causing diseases and significant economic losses of plants in the Cupressaceae and Rosaceae family (Kern 1973). During our investigation of rust fungi in Qinghai Province, northwestern China, we found the spermogonial and aecial stages of Gymnosporangium species on Cotoneaster acutifolius. C. acutifolius is the woody plant that range in habit from ground-covers to airy shrubs and medium-sized trees(Rothleutner et al. 2016). Upon investigation in the field, the incidence of rust on C. acutifolius was 80% and 60% (n = 100) for 2020 and 2022, respectively. C. acutifolius leaves showing abundant aecia were collected from Batang forest area of Yushu (32.45°N, 97.19°E, alt. 3835 m), Qinghai, China, from August to October of both years. The rust makes its symptom first on the upper surface appearing yellow then dark brow, aggregated spermogonia in yellow-orange leaf spots. These spots enlarge gradually and displaying an orange-yellow and are often bordered by red concentric rings. In the later stage, many pale yellow, roestelioid aecia developed on the abaxial surfaces of the leaves or fruits. The morphology of this fungus was studied using light microscopy and scanning electron microscopy (JEOL, JSM-6360LV). Microscopic examination show that aecia are foliicolous, hypophyllous, roestelioid, and producing cylindrical peridia that are acuminate, splitting above and becoming some-what lacerate nearly to base, somewhat erect after dehiscence. Peridial cells are rhomboid, and 42 to 118 × 11-27μm(n=30). They have smooth outer walls and rugose inner and side walls with long obliquely arranged ridges. Aeciospores are ellipsoid, chestnut brown, 20 to 38 × 15 to 35 μm(n=30), wall densely and minutely verrucose, 1 to 3 μm thick, with 4 to 10 pores. Whole genomic DNA was extracted (Tian et al. 2004), and the internal transcribed spacer 2 (ITS2) region was amplified with the primer pair ITS3 (Gardes and Bruns 1993) and ITS4 (Vogler and Bruns 1998). The sequence of the amplified fragment was deposited in the GenBank database (GenBank Accession No. MW714871). A BLAST search of GenBank showed a high identity (> 99%) with the reference sequences of Gymnosporangium pleoporumGenBank Accession No. MH178659 and MH178658). G. pleoporum was first described from specimens in the telial stage found on Juniperus przewalskii, from Menyuan of Qinghai in China (Tao et al. 2020). In this study, the fungus G.pleoporum of spermogonial and aecial stages were collected from the C. acutifolius, we confirmed the alternate host of G. pleoporum based on DNA extraction results. To our knowledge, this is the first record of G. pleoporum causing rust disease on C. acutifolius. Because the alternate host can be infected by several different species of Gymnosporangium (Tao et al. 2020), further investigations are needed to verify heteroecious of the rust fungus.

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.

Gymnosporangium species occurring on Juniperus and Pyrus in Latvia and evidence for Gymnosporangium clavariiforme infecting European pear (Pyrus communis)

Gymnosporangium species occurring on Juniperus and Pyrus in Latvia and evidence for Gymnosporangium clavariiforme infecting European pear (Pyrus communis)

Comparative transcriptomic analysis of the haustoria of Gymnosporangium yamadae and G. asiaticum

To provide a theoretical basis for controlling the spread of rust disease, cultivating disease-resistant varieties and reducing yield losses, we investigated the transcriptome differences between Gymnosporangium yamadae and Gymnosporangium asiaticum at the haustorial stage and revealed a specialized selection mechanism for Gymnosporangium species to infect host plants. We sequenced the transcriptomes of the haustoria in rust-infected leaves when basidiospores of G. yamadae and G. asiaticum infected their hosts, and obtained 21 213 and 13 015 unigenes, respectively. Real-time fluorescence quantitative PCR validation of five genes selected from G. yamadae and G. asiaticum, respectively, showed that their expression profiles were generally consistent with the results of transcriptome analysis, demonstrating the reliability of the transcriptome data. We used seven databases such as Nr, GO, KEGG, and KOG to perform gene function annotation and enrichment analysis, and found that the genes from both rusts were mainly enriched in cellular processes, translation, and metabolism-related pathways. Moreover, we used SignalP, TMHMM online website and other software such as dbCAN, BLSAT, HMMER to show that there were 343 (2.51%) and 175 (2.79%) candidate effector proteins containing 14 and 5 proteases and 10 and 3 lipases in the haustoria of G. yamadae and G. asiaticum, respectively. Furthermore, we used OrthoFinder, BLAST and KaKs Calculator software to analyze the evolutionary relationship of the two fungi. Among one-to-one homologous genes, gene pairs with > 82% alignment were considered to be under conservative selection, and 12.37% under positive selection. Five effectors of G. asiaticum were under positive selection, and one of which was a lipase. No significant differences were found in the enrichment of expressed genes between G. yamadae and G. asiaticum, indicating the biological processes involved in haustoria were relatively conserved, despite the typical host selectivity between species. The low protein similarity between the two species suggested that they were under greater host selective pressure and there was significant evolutionary divergence, which might be related to the host-specific selection mechanism. In the haustorial, the main purpose of the effectors might be to regulate physiological processes in the plants rather than attacking the host directly, and G. yamadae and G. asiaticum might use plant lipids as energy sources.

Identification and characterization of two new Gymnosporangium species causing rust on Juniperus rigida in China

ABSTRACT A serious Juniperus rigida rust disease was found in Gansu Province, China. The disease incidence is approximately 80–90%. We also found rust disease on both Cotoneaster multiflorus and Sorbus in the same location. Two novel Gymnosporangium species were identified from the infected plants. Based on morphological observations and phylogenetic analyses, we describe the two new taxa as G. gansuense and G. granulatosporum. We also determined their life cycles. Moreover, this study documented a novel aeciospore surface structure with two different surface types on one aeciospore. We describe it here as “granular.”

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.

Species diversity, taxonomy, and phylogeny of Gymnosporangium in China

ABSTRACT Gymnosporangium is a group of plant fungal pathogens that cause rust diseases on many economically important fruit trees. Most Gymnosporangium are heteroecious and demicyclic, producing four morphologically diverse spore stages on two taxonomically unrelated host plants, the Cupressaceae and Rosaceae. The complex life cycle and heteroecism make it difficult to investigate the species within Gymnosporangium. To determine the taxonomy, phylogeny, and species diversity of Gymnosporangium in China, a large collection of 672 specimens were analyzed using a combination of morphological observations and phylogenetic analyses. In total, 27 Gymnosporangium species from China are documented here, including 22 known species, one new combination, one new record, and three new species. The study also documents a novel aeciospore surface structure with an irregular surface that is described here as “surfy.”

Development of SSR markers from transcriptome data for the pear rust pathogen Gymnosporangium asiaticum

AbstractThe pear‐cypress rust Gymnosporangium asiaticum is one of the most significant causal agents of pear rust in Asian pear, severely affecting the pear industry. Research on the genetic diversity of this widespread pathogen has been hampered due to the absence of molecular markers. In the current study, we developed 16 novel microsatellite markers for G. asiaticum from transcriptome data by combining next‐generation sequencing and PCR screening. These polymorphic markers were tested on 96 individuals from nine provinces in China. The number of alleles for these markers ranged from two to nine, with an average of five at each locus. The polymorphic information content ranged from 0.0411 to 0.7666, with an average of 0.4417. In addition, the observed (HO) and expected (HE) heterozygosities were 0.0312–0.6941 and 0.0417–0.8000, respectively. We also observed low‐to‐moderate levels of genetic differentiation and extremely significant gene flow between the nine provinces. Of these 16 developed simple sequence repeat loci, 11 were transferable to other Gymnosporangium species. These new microsatellite markers can be used in future large‐scale studies of the genetic structure and diversity of G. asiaticum.

Gymnosporangium species on Malus: species delineation, diversity and host alternation.

Gymnosporangium species (Pucciniaceae, Pucciniales, Basidiomycota) are the causal agents of cedar-apple rust diseases, which can lead to significant economic losses to apple cultivars. Currently, the genus contains 17 described species that alternate between spermogonial/aecial stages on Malus species and telial stages on Juniperus or Chamaecyparis species, although these have yet to receive a modern systematic treatment. Furthermore, prior studies have shown that Gymnosporangium does not belong to the Pucciniaceae sensu stricto (s.str.), nor is it allied to any currently defined rust family. In this study we examine the phylogenetic placement of the genus Gymnosporangium. We also delineate interspecific boundaries of the Gymnosporangium species on Malus based on phylogenies inferred from concatenated data of rDNA SSU, ITS and LSU and the holomorphic morphology of the entire life cycle. Based on these results, we propose a new family, Gymnosporangiaceae, to accommodate the genus Gymnosporangium, and recognize 22 Gymnosporangium species parasitic on Malus species, of which G. lachrymiforme, G. shennongjiaense, G. spinulosum, G. tiankengense and G. kanas are new. Typification of G. asiaticum, G. fenzelianum, G. juniperi-virginianae, G. libocedri, G. nelsonii, G. nidus-avis and G. yamadae are proposed to stabilize the use of names. Morphological and molecular data from type materials of 14 Gymnosporangium species are provided. Finally, morphological characteristics, host alternation and geographical distribution data are provided for each Gymnosporangium species on Malus.

Comparative transcriptomics of Gymnosporangium spp. teliospores reveals a conserved genetic program at this specific stage of the rust fungal life cycle

BackgroundGymnosporangium spp. are fungal plant pathogens causing rust disease and most of them are known to infect two different host plants (heteroecious) with four spore stages (demicyclic). In the present study, we sequenced the transcriptome of G. japonicum teliospores on its host plant Juniperus chinensis and we performed comparison to the transcriptomes of G. yamadae and G. asiaticum at the same life stage, that happens in the same host but on different organs.ResultsFunctional annotation for the three Gymnosporangium species showed the expression of a conserved genetic program with the top abundant cellular categories corresponding to energy, translation and signal transduction processes, indicating that this life stage is particularly active. Moreover, the survey of predicted secretomes in the three Gymnosporangium transcriptomes revealed shared and specific genes encoding carbohydrate active enzymes and secreted proteins of unknown function that could represent candidate pathogenesis effectors. A transcript encoding a hemicellulase of the glycoside hydrolase 26 family, previously identified in other rust fungi, was particularly highly expressed suggesting a general role in rust fungi. The comparison between the transcriptomes of the three Gymnosporangium spp. and selected Pucciniales species in different taxonomical families allowed to identify lineage-specific protein families that may relate to the biology of teliospores in rust fungi. Among clustered gene families, 205, 200 and 152 proteins were specifically identified in G. japonicum, G. yamadae and G. asiaticum, respectively, including candidate effectors expressed in teliospores.ConclusionsThis comprehensive comparative transcriptomics study of three Gymnosporangium spp. identified gene functions and metabolic pathways particularly expressed in teliospores, a stage of the life cycle that is mostly overlooked in rust fungi. Secreted protein encoding transcripts expressed in teliospores may reveal new candidate effectors related to pathogenesis. Although this spore stage is not involved in host plant infection but in the production of basidiospores infecting plants in the Amygdaloideae, we speculate that candidate effectors may be expressed as early as the teliospore stage for preparing further infection by basidiospores.

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.

Comparative transcriptome analysis and identification of candidate effectors in two related rust species (Gymnosporangium yamadae and Gymnosporangium asiaticum)

BackgroundRust fungi constitute the largest group of plant fungal pathogens. However, a paucity of data, including genomic sequences, transcriptome sequences, and associated molecular markers, hinders the development of inhibitory compounds and prevents their analysis from an evolutionary perspective. Gymnosporangium yamadae and G. asiaticum are two closely related rust fungal species, which are ecologically and economically important pathogens that cause apple rust and pear rust, respectively, proved to be devastating to orchards. In this study, we investigated the transcriptomes of these two Gymnosporangium species during the telial stage of their lifecycles. The aim of this study was to understand the evolutionary patterns of these two related fungi and to identify genes that developed by selection.ResultsThe transcriptomes of G. yamadae and G. asiaticum were generated from a mixture of RNA from three biological replicates of each species. We obtained 49,318 and 54,742 transcripts, with N50 values of 1957 and 1664, for G. yamadae and G. asiaticum, respectively. We also identified a repertoire of candidate effectors and other gene families associated with pathogenicity. A total of 4947 pairs of putative orthologues between the two species were identified. Estimation of the non-synonymous/synonymous substitution rate ratios for these orthologues identified 116 pairs with Ka/Ks values greater than1 that are under positive selection and 170 pairs with Ka/Ks values of 1 that are under neutral selection, whereas the remaining 4661 genes are subjected to purifying selection. We estimate that the divergence time between the two species is approximately 5.2 Mya.ConclusionThis study constitutes a de novo assembly and comparative analysis between the transcriptomes of the two rust species G. yamadae and G. asiaticum. The results identified several orthologous genes, and many expressed genes were identified by annotation. Our analysis of Ka/Ks ratios identified orthologous genes subjected to positive or purifying selection. An evolutionary analysis of these two species provided a relatively precise divergence time. Overall, the information obtained in this study increases the genetic resources available for research on the genetic diversity of the Gymnosporangium genus.

Gymnosporangium Species – An Important Issue of Plant Protection

Abstract Rusts (Fungi, Basidiomycota, Pucciniomycotina, Pucciniomycetes, Pucciniales) are one of the most important causal agents of diseases and they are infecting many plants including cereals and field crops, vegetables, trees and many ornamentals. They have been studied for a long time and have economic importance among the plant diseases caused by agents of different species of fungi. In Europe, thirteen rust genera have been reported, of which the genus Gymnosporangium is the second largest after genus Phragmidium. The most significant fruit tree rust pathogen is the genus Gymnosporangium. The literature review shows quite limited scientific information about this genus and its species. Studies have mainly focused on some stages of the pathogen development cycle, which are significant for the spread of diseases - uredo and teleito stages. Special attention of the review was paid to European pear rust (caused by G. sabinae (Dicks.) G. Winter), the distribution of which has increased during the last ten years, especially in organic pear orchards. Currently there is a limited number of scientific publications about European pear rust, and they are mainly based only on observations in vitro without trials in the field, despite the fact that it has become one of the most devastating diseases. Therefore, the presented review analyses the rust exploration history, diversity and distribution of species, life cycle, development biology and plant protection issues.

Gymnosporangium przewalskii sp. nov. (Pucciniales, Basidiomycota) from China and its life cycle

In an investigation of rust fungi in Qinghai Province, northwestern China, the novel rust species Gymnosporangium przewalskii was identified based on morphology and phylogenetic analyses. Phylogenetic analyses using the internal transcribed spacers (ITS) and the large subunit (LSU) rRNA partial gene revealed that G. przewalskii is monophyletic and distinct from other Gymnosporangium species. The life cycle of this new taxon was clarified based on molecular data. Its spermogonial and aecial stages occurred on Sorbus koehneana, and its telial stage was found on Juniperus przewalskii.

Gymnosporangium huanglongense sp. nov. from western China

A novel rust species, Gymnosporangium huanglongense, was detected on Juniperus przewalskii in China. This species was characterized by the basal cell of its two-celled teliospores possessing two pores near the septum, and the distal cell possessing either two pores near the septum or occasionally an apical pore and one pore near the septum. It was also separated from other Gymnosporangium species based on analyses of internal transcribed spacer region and LSU rDNA partial gene sequences.

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.

Gymnosporangium spp. (non‐European)

<i>Gymnosporangium</i> spp. (non‐European)

Sorting out Gymnosporangium species – the aecial stage

Sorting out Gymnosporangium species – the aecial stage

Identification of Aecial Host Ranges of Four Korean Gymnosporangium Species Based on the Artificial Inoculation with Teliospores Obtained from Various Forms of Telia

The objectives of this study were to identify the aecial host ranges of four Korean Gymnosporangium species,G. asiaticum, G. cornutum, G. japonicum and G. yamadae, and to verify the morphological characteristics of telia as diagnostic keys to the species. Thirteen Korean Rosaceous woody species were artificially inoculated with teliospores obtained from Juniperus species. There was high specificity between telial and aecial hosts and the fungal species, providing the first experimental proof on host alternation of these rust fungi in Korea.Telia on the witches` broom and on the small galls were identified as new telial characteristics in G. asiaticum and in G. yamadae, respectively. Aecial hosts of G. asiaticum and G.yamadae showed varying responses in their susceptibility and in the days required for formation and duration of spermogonia and aecia after inoculation. Four telial host species in Juniperus were confirmed for the first time in Korea, which include J. chinensis var. kaizuka, J. chinensis var. horizontalis and J. chinensis var. globosa for G. asiaticum; and J. chinensis var. kaizuka for G. yamadae.

Two Newly Identified Gymnosporangium Species, G. japonicum and G. cornutumn, in Korea

Two Gymnosporangium species, G. japonicum and G. cornutum, causing cedar-apple rust, were newly identified in Korea, and a new aecial host for each fungus was found by artificial inoculation. Detailed descriptions of the species were made based on macroscopic features (symptoms and signs) and light and scanning electron microscopic observations of spores and peridial cells. G. japonicum from Juniperus chinensis var. horizontalis had Photinia villosa as its new aecial host G. cornutum from J. rigida showed its aecial stage on Sorbus alnifolia.