Rust Fungus Research Articles

Linking symbioses with intrinsic chemical defences in conifers: Fungal‐mediated resistance against an invasive pathogen

Abstract Invasive pathogens threaten the sustainability of forest ecosystems globally. Trees possess intrinsic pathogen defence mechanisms, including major gene resistance (MGR) and quantitative disease resistance (QDR). Plant‐symbiotic fungi can enhance tree defences, generating far‐reaching ecosystem impacts. However, the specific contributions of various fungal guilds to this symbiont‐mediated resistance remain unclear. In this study, we inoculated six Pinus monticola seedling families exhibiting resistance (MGR or QDR) or high susceptibility to the introduced invasive pathogen Cronartium ribicola, the causative agent of white pine blister rust (WPBR), with endophytic and ectomycorrhizal fungi, either alone or in combination (symbiont treatments), in an open‐air greenhouse study. Over a period of 25 months, we monitored the growth, foliar terpene defences, and disease progression in trees before and after C. ribicola infection and in trees inoculated with the symbionts but never inoculated with C. ribicola. We observed enhanced inducible host defences and evidence of defensive priming in response to symbiont treatments. In WPBR‐free control treatments, differences in pine defences coincided with an increased seedling growth rate. For WPBR‐infected seedlings, symbiont treatments reduced disease symptoms in seedlings with QDR and to a lesser extent in susceptible families, but not in those with MGR. Furthermore, disease symptoms correlated with variations in terpene composition. Synthesis and applications: Interactions with fungal symbionts should be considered when breeding native trees for resistance against invasive pathogens. Our study underscores the capacity of endophytic and ectomycorrhizal fungi to enhance tree growth and defence while also reducing disease symptoms. We also show that fungi can induce long‐lasting changes in conifer foliar terpenes, suggesting potential applications in tree protection from invasive pathogens.

Confirmation of oat crown rust disease in Taiwan.

Oat is a minor forage crop grown in Taiwan. Only a few historical records of oat rust disease have been reported in the country. Therefore, the pathogen population remains poorly characterized. A rust-like disease outbreak was detected at the Experimental Farm of National Taiwan University in 2019, which caused significant damage to field experiments. To determine the identity of the pathogen responsible for this disease outbreak, we collected infected foliar material. Disease signs suggested infection by the oat crown rust fungus. Hence, common procedures in rust pathology were applied to confirm the identity of the pathogen with phenotypic and molecular diagnostic techniques. A total of 50 field pathogen samples from infected oat cultivars were collected in 2019 and five single pustule rust isolates were obtained in 2020 and 2021. These isolates were initially identified as Puccinia coronata var. avenae f. sp. avenae (Pca) based on the phylogenetic analysis of nrITS sequence data. This identification was subsequently confirmed through whole-genome phylogeny, which showed that the representative Taiwanese isolate NTU1 clustered with other Pca representative strains in Basidiomycota. Phenotyping assays across 36 oat differential lines demonstrated that Taiwanese isolates are phenotypically similar with relatively low virulence. This study presents the first molecular confirmation of Pca in Taiwan and reports the virulence profiles of Taiwanese Pca population.

Rust fungi (Pucciniales) on Cyperaceae in Japan, with 2 new names, 5 new combinations and typifications

Rust fungi (Pucciniales) producing uredinial and/or telial stages on species of Cyperaceae in Japan are listed based on literature records. Host plants and distribution of 92 species (86 species of Puccinia, 5 species of Uromyces and 1 species of Uredo) are described. Among them two new names and five new combination names are proposed in accordance with the Shenzhen Code, ICNafp. Type specimens (neotypes, lectotypes, epitypes, paratypes) for 29 species are selected and designated. One hundred species of Cyperaceae (22.9% of species reported in Japan) including ten genera are recorded as their host plants of uredinial and/or telial stages. Spermogonial and aecial stages of 36 species are confirmed and 59 species of plants including 14 families 29 genera are also described as their hosts.

First European records of Puccinia modiolae and P. platyspora, two native South American rust fungi, and new observations on their life cycle and morphology

ABSTRACT This paper reports the South American rust fungi Puccinia modiolae and P. platyspora (Pucciniales/Uredinales) as new alien species of the European rust funga. Puccinia modiolae is presently known from Switzerland and Germany, P. platyspora from Switzerland, Germany, and France. The records of P. platyspora are the first ones from outside South America. The specimens were identified by teliospore characters and sequences of the nuclear ribosomal DNA (internal transcribed spacer 2 and domains D1–D2 of the nuclear ribosomal large subunit) and the mitochondrial CO3 (cytochrome c oxidase III) gene. Puccinia modiolae and P. platyspora have been recorded so far in Europe on members of the genera Alcea, predominantly on Alcea rosea, Althaea, and Malva of the Malvaceae, subfam. Malvoideae. Alcea rosea is host of both species and shared also with the common mallow rust, P. malvacearum, allowing for mixed infections. The plant is commonly grown as an ornamental and may play a major role for the spread of the alien Malvaceae rust fungi. It was observed for the first time that P. platyspora can produce spermogonia and aecidium-type aecia, suggesting phenotypic plasticity regarding the formation of spore states. The observed spermogonia mainly remained closed and did not liberate spermatia. They produced telio- and aeciospores besides spermatia in their cavity and eventually converted entirely into telia or, rarely, into aecidium-like sori. Small clusters of aeciospores and peridial cells were commonly found hidden in the telial plectenchyma, and well-developed aecidium-type aecia provided with a peridium developed rarely in the center of mature telia. Spermogonia belonging to group V type 4 were found in P. malvacearum, which is generally supposed to lack spermogonia. Some spermogonia produced only spermatia in their cavity; others formed spermatia and teliospores, and some eventually converted into telia.

Virulence of Puccinia coronata var avenae f. sp. avenae (oat crown rust) in Canada during 2016 to 2020 and comparison of extensive vs intensive sampling methods

Puccinia coronata var avenae f. sp. avenae (Pca), the causal fungus of crown rust of oats, is a significant threat to oat production in the eastern prairie region (Manitoba and eastern Saskatchewan; EPR), Ontario and Quebec (eastern Canada; EC), in Canada. Development of oat lines with effective resistance to Pca has been a priority for oat breeding programmes in Canada, and helped mitigate reductions in oat yield and quality. This requires knowledge of the virulence characteristics of the Pca population in Canada. Our objectives were to determine the incidence and severity of Pca in Canada, the presence and frequency of virulence and races in Pca populations and compare the traditional extensive sampling method (few isolates per field from many fields) to an intensive sampling method (many isolates per field from a few fields) for obtaining genetically diverse collections. The incidence and severity of crown rust of oat in Canada was lower in 2016 to 2020 than has been reported in previous years. Virulence to all the 24 Pc genes studied was observed over the 5 years in EC and the EPR. The most effective genes were Pc94, Pc98 and Pc101 in EC and Pc50, Pc96, Pc97 and Pc98 in the EPR. Approximately 81% of 424 races identified were of unique virulence phenotypes over the 5 years, indicating a highly variable Pca population in Canada. Races JTQG-91 and GTQG-91 were the most common races identified. Collections of Pca obtained using the extensive sampling method were observed to be more genetically diverse than collections obtained using the intensive sampling method in 2018 and 2020, but not in 2019.

The Genus Ravenelia: Insights on Taxonomy, Diversity and Distribution.

Ravenelia is the third largest rust genus of the order Pucciniales with more than 200 described species. It is an important rust genus that has undergone tremendous taxonomic changes. This genus produces teliospores united into a head on a compound pedicel composed of two to several hyphae with autoecious, macro-, demi- to hemi-, and, more rarely, microcyclic modes of their life cycle which provide it a unique identity and have proved helpful in the identification of the genus. The current understanding of the taxonomy, history, diversity and distribution of this genus is discussed in this paper. Both online and offline resources were searched to gather data of the published literature. The data thus obtained were analyzed for numerical and graphical summaries to provide the diversity and distribution of the genus. In addition, a phylogenetic analysis based on the ITS and nLSU DNA sequence data available in GenBank and the published literature was performed to examine the taxonomic placement of different species within the genus. The genus was reported to be distributed over 53 countries of the world. Around 51 plant genera belonging to four plant families, viz., Fabaceae, Phyllanthaceae, Asphodelaceae and Zygophyllaceae were found to be infected with these rust fungi. The phylogenetic analysis based on LSU and ITS sequence data revealed the polyphyletic nature of the genus. A table of 248 species of this genus is also provided with all information of host, distribution and cited reference that can be helpful for mycologists to find all information at one place. Future perspectives for the advancement of this genus are also discussed.

Exploitation of the genetic potential of Thinopyrum and Agropyron genera to protect wheat from diseases and environmental stresses.

Common wheat is one of the most important food crops in the world. Grain harvests can be increased by reducing losses from diseases and environmental stresses. The tertiary gene pool, including Thinopyrum spp., is a valuable resource for increasing genetic diversity and wheat resistance to fungal diseases and abiotic stresses. Distant hybridization between wheat and Thinopyrum spp. began in the 1920s in Russia, and later continued in different countries. The main results were obtained using the species Th. ponticum and Th. intermedium. Additionally, introgression material was created based on Th. elongatum, Th. bessarabicum, Th. junceiforme, Agropyron cristatum. The results of introgression for resistance to diseases (leaf, stem, and stripe rusts; powdery mildew; Fusarium head blight; and Septoria blotch) and abiotic stresses (drought, extreme temperatures, and salinity) to wheat was reviewed. Approaches to improving the agronomic properties of introgression breeding material (the use of irradiation, ph-mutants and compensating Robertsonian translocations) were described. The experience of long-term use in the world of a number of genes from the tertiary gene pool in protecting wheat from leaf and stem rust was observed. Th. ponticum is a nonhost for Puccinia triticina (Ptr) and P. graminis f. sp. tritici (Pgt) and suppresses the development of rust fungi on the plant surface. Wheat samples with the tall wheatgrass genes Lr19, Lr38, Sr24, Sr25 and Sr26 showed defence mechanisms similar to nonhosts resistance. Their influence led to disruption of the development of surface infection structures and fungal death when trying to penetrate the stomata (prehaustorial resistance or stomatal immunity). Obviously, a change in the chemical properties of fungal surface structures of races virulent to Lr19, Lr24, Sr24, Sr25, and Sr26 leads to a decrease in their adaptability to the environment. This possibly determined the durable resistance of cultivars to leaf and stem rusts in different regions. Alien genes with a similar effect are of interest for breeding cultivars with durable resistance to rust diseases and engineering crops with the help of molecular technologies.

Questioning the effectiveness of seed-reducing agents on invasive Acacia: Pod production relative to gall abundance of classical biological control agents

It has been widely accepted that the biological control agents released on invasive Australian Acacia in South Africa, have impacted on the population dynamics of their host plants. However, there are no quantitative data to support these claims and these invasive species remain at similar abundance levels prior to the release of their associated biological control agents and also show evidence of range expansion. The effect of biological control agents, two bud galling wasps (Trichilogaster acaciaelongifoliae and T. signiventris) and one gall-forming rust fungus (Uromycladium morrisii), on the pod production of their respective hosts (Acacia longifolia, A. pycnantha and A. saligna) was assessed by quantifying the reproductive and galled trees per hectare as well as the pods and galls produced per tree and per square meter over a one to two year period. It was shown that invasive Australian Acacia satiate their gall-forming biological control agents, with many pods surviving in their presence. Pod production and loss was placed into perspective using recent findings of seed rain and seed bank studies. It was concluded, based on pod production, seed rain and seed bank data that despite T. acaciaelongifoliae, T. signiventris and U. morrisii reducing pod production, they have had no impact on the population dynamics of their invasive Australian Acacia hosts in South Africa.

Wheat Leaf Rust Fungus Effector Protein Pt1641 Is Avirulent to TcLr1.

Wheat leaf rust fungus is an obligate parasitic fungus that can absorb nutrients from its host plant through haustoria and secrete effector proteins into host cells. The effector proteins are crucial factors for pathogenesis as well as targets for host disease resistance protein recognition. Exploring the role of effector proteins in the pathogenic process of Puccinia triticina Eriks. (Pt) is of great significance for unraveling its pathogenic mechanisms. We previously found that a cysteine-rich effector protein, Pt1641, is highly expressed during the interaction between wheat and Pt, but its specific role in pathogenesis remains unclear. Therefore, this study employed techniques such as heterologous expression, qRT-PCR analysis, and host-induced gene silencing (HIGS) to investigate the role of Pt1641 in the pathogenic process of Pt. The results indicate that Pt1641 is an effector protein with a secretory function and can inhibit BAX-induced programmed cell death in Nicotiana benthamiana. qRT-PCR analyses showed that expression levels of Pt1641 were different during the interaction between the high-virulence strain THTT and low-virulence strains FGD and Thatcher, respectively. The highest expression level in the low-virulence strain FGD was four times that of the high-virulence strain THTT. The overexpression of Pt1641 in wheat near-isogenic line TcLr1 induced callose deposition and H2O2 production on TcLr1. After silencing Pt1641 in the Pt low-virulence strain FGD on wheat near-isogenic line TcLr1, the pathogenic phenotype of Pt physiological race FGD on TcLr1 changed from ";" to "3", indicating that Pt1641 plays a non-toxic function in the pathogenicity of FGD to TcLr1. This study helps to reveal the pathogenic mechanism of wheat leaf rust and provides important guidance for the mining and application of Pt avirulent genes.

Soybean transcription factor GmNF-YB20 confers resistance to stripe rust in transgenic wheat by regulating nonspecific lipid transfer protein genes.

Worldwide food security is severely threatened by the devastating wheat stripe rust disease. The utilization of resistant wheat cultivars represents the most cost-effective and efficient strategy for combating this disease. However, the lack of resistant resources has been a major bottleneck in breeding for wheat disease resistance. Therefore, revealing novel gene resources for combating stripe rust and elucidating the underlying resistance mechanism is of utmost urgency. In this study, we identified that the soybean NF-YB transcription factor GmNF-YB20 in wheat provides resistance to the stripe rust fungus (Puccinia striiformis f. sp. tritici, Pst). Wheat lines with stable overexpression of the GmNF-YB20 enhanced resistance against multiple Pst races. Transcriptome profiling of GmNF-YB20 transgenic wheat under Pst infection unveiled its involvement in the lipid signaling pathway. RT-qPCR assays suggested that GmNF-YB20 increased transcript levels of multiple nonspecific lipid transfer protein (LTP) genes during wheat-Pst interaction, luciferase reporter analysis illustrates that it activates the transcription of TaLTP1.50 in wheat protoplast, and GmNF-YB20 overexpressed wheat plants had higher total LTP content in vivo during Pst infection. Overexpression of TaLTP1.50 in wheat significantly increased resistance to Pst, whereas knockdown of TaLTP1.50 exhibited the opposite trends, indicating that TaLTP1.50 plays a positive role in wheat resistance. Taken together, our findings provide perspective regarding the molecular mechanism of GmNF-YB20 in wheat and highlight the potential use for wheat breeding.

Genetically-clustered antifungal phytocytokines and receptor protein family members cooperate to trigger plant immune signaling.

Phytocytokines regulate plant immunity by cooperating with cell-surface proteins. Populus trichocarpa RUST INDUCED SECRETED PEPTIDE 1 (PtRISP1) exhibits an elicitor activity in poplar, as well as a direct antimicrobial activity against rust fungi. PtRISP1 gene directly clusters with a gene encoding a leucine-rich repeat receptor protein (LRR-RP), that we termed RISP-ASSOCIATED LRR-RP (PtRALR). In this study, we used phylogenomics to characterize the RISP and RALR gene families, and molecular physiology assays to functionally characterize RISP/RALR pairs. Both RISP and RALR gene families specifically evolved in Salicaceae species (poplar and willow), and systematically cluster in the genomes. Despite a low sequence identity, Salix purpurea RISP1 (SpRISP1) shows properties and activities similar to PtRISP1. Both PtRISP1 and SpRISP1 induced a reactive oxygen species (ROS) burst and mitogen-activated protein kinases (MAPKs) phosphorylation in Nicotiana benthamiana leaves expressing the respective clustered RALR. PtRISP1 also triggers a rapid stomatal closure in poplar. Altogether, these results suggest that plants evolved phytocytokines with direct antimicrobial activities, and that the genes coding these phytocytokines co-evolved and physically cluster with genes coding LRR-RPs required to initiate immune signaling.

Characterization of the fungal genus Sphaerellopsis associated with rust fungi: species diversity, host-specificity, biogeography, and in-vitro mycoparasitic events of S. macroconidialis on the southern corn rust, Puccinia polysora

Sphaerellopsis species are putative hyperparasites of rust fungi and may be promising biological control agents (BCA) of rust diseases. However, few detailed studies limit potential BCA development in Sphaerellopsis. Here, we explored the biogeography, host-specificity, and species diversity of Sphaerellopsis and examined the early infection stage of one species, S. macroconidialis, to infer its trophic status. We randomly screened 5,621 rust specimens spanning 99 genera at the Arthur Fungarium for the presence of Sphaerellopsis. We identified 199 rust specimens infected with Sphaerellopsis species on which we conducted morphological and multi-locus phylogenetic analyses. Five Sphaerellopsis species were recovered, infecting a total of 122 rust species in 18 genera from 34 countries. Sphaerellopsis melampsorinearum sp. nov. is described as a new species based on molecular phylogenetic data and morphological features of the sexual and asexual morphs. Sphaerellopsis paraphysata was the most commonly encountered species, found on 77 rust specimens, followed by Sphaerellopsis macroconidialis on 56 and S. melampsorinearum on 55 examined specimens. The type species, Sphaerellopsis filum, was found on 12 rust specimens and Sphaerellopsis hakeae on a single specimen. We also recovered and documented for the first time, the sexual morph of S. macroconidialis, from a specimen collected in Brazil. Our data indicate that Sphaerellopsis species are not host specific and furthermore that most species are cosmopolitan in distribution. However, S. paraphysata is more abundant in the tropics, and S. hakeae may be restricted to Australia. Finally, we confirm the mycoparasitic strategy of S. macroconidialis through in-vitro interaction tests with the urediniospores of Puccinia polysora. Shortly after germination, hyphae of S. macroconidialis began growing along the germ tubes of P. polysora and coiling around them. After 12 days of co-cultivation, turgor loss was evident in the germ tubes of P. polysora, and appressorium-like structures had formed on urediniospores. The interaction studies indicate that Sphaerellopsis species may be more effective as a BCA during the initial stages of rust establishment.

New species, names, and type designation of rust fungi from New Zealand

ABSTRACT Rust fungi are obligate plant pathogens, usually restricted to a single host species or genus, although some species such as myrtle rust (Austropuccinia psidii) and some cereal and grass rusts (Puccinia spp.) can infect many members of the families Myrtaceae and Poaceae, respectively. The rust life cycle can involve up to five spore stages, both sexual and asexual. The cycle may be completed on a single host (autoecious rust) or require two, unrelated host plants (heteroecious rust) for completion. About 300 rust species are known in New Zealand, with approximately half comprising native rusts (usually pathogenic on native plants) and half being introduced rusts (usually pathogenic on exotic plants). In this paper, 26 new species of rust fungi discovered in New Zealand are described, comprising one species each of Aecidium and Milesina, two of Pucciniastrum, four of Uromyces and 18 of Puccinia. Puccinia ferocis-forsteri is a new heteroecious species producing uredinia and telia on the endemic Carex forsteri and aecia on endemic Urtica ferox. This is only the third native heteroecious rust fungus reported in New Zealand. In addition, two species are transferred to the genus Milesina, three to Uromyces and seven to Puccinia (including a nom. nov.), either following discovery of the sexual (telial) stage of these rusts or considering the most appropriate sexual genus. A new combination is proposed for Coleosporium based on morphology of its urediniospores and molecular data. Epitypes are designated for eight species, lectotypes are selected for five species and a neotype is designated. Apart from one new species on the introduced Fuchsia magellanica all the rusts are considered native to New Zealand. Where appropriate, DNA was extracted and the 28S region (nuclear large subunit ribosomal DNA [nuLSU]) was amplified with the resulting LSU sequences aligned with sequences from GenBank representing most of the major clades.

The nematode signaling molecule ascr#18 induces prepenetration defenses in wheat against a leaf rust fungus

Leaf rust, caused by the pathogenic biotrophic rust fungus Puccinia triticina (Pt), is one of the most destructive wheat diseases worldwide; its negative impact on crop yields is exacerbated by increasing temperatures due to climate change. Ascarosides are nematode pheromones that induce resistance to microbial pathogens and pests in a wide range of crops, making them valuable components in biocontrol scenarios. We investigated the effect on infection of various wheat (Triticum aestivum) genotypes with the virulent Pt race 77W × R by ascr#18, the major ascaroside secreted into the rhizosphere by plant-parasitic nematodes. Spraying the leaves with ascr#18 24 h before inoculation with fungal uredospores slowed disease development and resulted in a reduction of the number of rust pustules on treated compared to untreated leaves. Dose–response analysis over the nano- and micromolar range revealed a broad optimum concentration down to 0.01nM ascr#18. Microscopic analysis showed very early arrest of the fungus at the appressorial stage, with associated enhanced local accumulation of H2O2 and abortive stoma penetration. Similarly, ascr#18 also induced strong resistance to Pt race PKTTS, confirming its race-unspecific biocontrol activity. The results of this study are consistent with and extend previous research that has shown that ascr#18 activates plant immunity and thus protects plants from pathogens even at very low doses.

First record of the rust fungus Uromyces gageae on Yellow Star-of-Bethlehem (Gagea lutea) in the Netherlands.

Yellow Star-of-Bethlehem (Gagea lutea) is a rare and threatened bulbous plant in the Netherlands, with its largest stronghold in the northern province of Drenthe. In 2022, numerous plants within a population of G. lutea were found to be infected by a rust fungus, which was identified as Uromyces gageae based on morphological characteristics. Further examination of collected teliospores revealed differences from Uromyces acutatus, a closely related rust species known to infect Ornithogalum and Gagea species. Rust symptoms on G. lutea plants were observed within the same population in April 2023, suggesting that teliospores surviving winter conditions serve as a viable source for recurrent infection. DNA of U. gageae and U. acutatus extracted from teliospores was used to obtain partial ribosomal DNA (rDNA) gene fragments by PCR. Amplicon sequencing revealed nucleotide variation between both rust species and verified the identity of the rust fungus on G. lutea as U. gageae. This confirmation substantiates the first documentation of U. gageae in the Netherlands. This study raises new avenues for research on the distribution and host range of U. gageae, as well as additional studies on the population dynamics of this potentially rare, wild plant-rust interaction.

Phylogeny, biogeography, and host range of gall midges (Diptera: Cecidomyiidae) feeding on spores of rust fungi (Basidiomycota: Pucciniales).

Rust fungi (Pucciniales) are plant pathogens that can cause devastating yield losses to economically important crops and threaten native plants with extinction. Rusts are usually controlled with fungicides when rust-resistant plant varieties are unavailable. However, natural enemies may offer an alternative to chemicals by acting as biological controls. The larvae of Mycodiplosis Rübsaamen (49 spp.) feed on the spores of rusts and powdery mildew fungi and have been suggested as a potential biocontrol candidate for disease-causing rusts. However, little is known about the phylogenetic relationships, biogeography, and host range of this genus. We screened 5,665 rust specimens from fungarium specimens and field collections and recovered a total of 363 larvae on 315 rust specimens from 17 countries. Three mitochondrial and 2 nuclear loci were amplified and sequenced for the phylogenetic reconstruction of 129 individuals. We recovered 12 clades, of which 12 and 10 were supported with maximum likelihood and Bayesian inference, respectively. Of the 12 clades, 7 comprised species from multiple continents and climatic regions, and 5 comprised species from a single region. Individuals forming clades were collected from 2 to 18 rust species, suggesting that Mycodiplosis species have a broad host range. In total, Mycodiplosis larvae were identified on 44 different rust species collected from 18 plant families. Future studies should focus on expanding field sampling efforts, including data from additional gene regions, and incorporating morphological data to further elucidate species diversity and distribution patterns.

Evasion of wheat resistance gene Lr15 recognition by the leaf rust fungus is attributed to the coincidence of natural mutations and deletion in AvrLr15 gene.

Employing race-specific resistance genes remains an effective strategy to protect wheat from leaf rust caused by Puccinia triticina (Pt) worldwide, while the newly emerged Pt races, owing to rapid genetic evolution, frequently overcome the immune response delivered by race-specific resistance genes. The molecular mechanisms underlying the newly evolved virulence Pt pathogen remain unknown. Here, we identified an avirulence protein AvrLr15 from Pt that induced Lr15-dependent immune responses. Heterologously produced AvrLr15 triggered pronounced cell death in Lr15-isogenic wheat leaves. AvrLr15 contains a functional signal peptide, localized to the plant nucleus and cytosol and can suppress BAX-induced cell death. Evasion of Lr15-mediated resistance in wheat was associated with a deletion and point mutations of amino acids in AvrLr15 rather than AvrLr15 gene loss in the Lr15-breaking Pt races, implying that AvrLr15 is required for the virulence function of Pt. Our findings identified the first molecular determinant of wheat race-specific immunity and facilitated the identification of the first AVR/R gene pair in the Pt-wheat pathosystem, which will provide a molecular marker to monitor natural Pt populations and guide the deployment of Lr15-resistant wheat cultivars in the field.

Advancing crop disease early warning in South Asia by complementing expert surveys with internet media scraping

AbstractWheat contributes one‐fifth of the global food supply with an estimated 29% of global production in low and lower‐middle income countries. As production expands across southern Asia, yields are often negatively impacted by outbreaks of fungal rust diseases. A wheat rust early warning and advisory system comprising surveillance, near real‐time disease risk forecasts and advisory dissemination has been established in two target countries in South Asia, including Nepal and Bangladesh. However, as wheat rust spores can be aerially transmitted over long distances, near real‐time estimates of disease incidence are required from sources of infection in neighbouring regions. To address this challenge, we developed and tested a novel algorithm to generate proxy observations of infection sources using online media reports in two neighbouring countries, India and Pakistan. Media sampling could provide an effective alternative where data from ground surveys are not readily available in near real‐time. Our results show that west Nepal was exposed to a substantial inoculum pressure from aerially dispersed stripe rust spores originating from India and Pakistan. There were no outbreaks of stripe rust disease in Bangladesh with only very low levels of cross‐border dispersion and generally unfavourable environmental conditions for infection. We further describe how proxy observations informed farmer decision‐making in near real‐time in Nepal and filled a knowledge gap in identifying early sources of infection for a major outbreak of stripe rust during 2020 in Nepal. Our results highlight the importance of international cooperation in mitigating transboundary plant pathogens.

Fruiting of Cronartium and Coleosporium rust fungi on Melampyrum spp. in Scots pine stands under various forest management applications in northern Finland

Cronartium pini is the causal agent of Scots pine blister rust in northern Europe. New silvicultural methods have recently been launched to manage Pinus sylvestris stands in Finland. Continuous-cover-forest management (CCF) is an approved alternative method for the traditional rotation-forest management (RF). The aim of this study was to compare fruiting and disease incidence of C. pini in forest stands managed applying the CCF and RF approaches. The incidence of C. pini-caused disease was assessed on P. sylvestris before, and on alternate herbaceous plant hosts Melampyrum pratense and M. sylvaticum one year after the CCF or RF application procedures and compared between several forest management types such as seed-tree cutting (STC), clearcutting (CC), gap cutting (GC), selection cutting (SC) and uncut control in seven study sites. Fruiting of the needle rust fungus, Coleosporium tussilaginis f. sp. melampyri, was also investigated. In 2020–2021, the number of P. sylvestris trees with symptoms of C. pini was low in all management types, and disease incidence varied from 0% to 2.8% among the management types. There was no statistically significant difference in the frequency of symptomatic pines between the management types and study sites at the beginning of the silvicultural management operations. Ten M. sylvaticum and/or M. pratense from five sample plots were collected in each managed stand. The incidence of symptomatic leaves of C. pini on M. sylvaticum varied from 0.6% to 7.7% among the management types and on M. pratense from 0% to 1.2% one year after the management applications. Coleosporium needle rust was more common than C. pini on Melampyrum spp. The percentage of leaves with C. tussilaginis f. sp. melampyri telia varied from 7.9% to 55.4% on M. pratense and from 0.6% to 24.8% on M. sylvaticum among the management types. The frequency of C. pini telia on M. pratense did not differ between the management types. The frequency of C. tussilaginis f. sp. melampyri telia on M. pratense did not differ between study sites, but it was significantly higher in unmanaged control stands compared to CC- or STC-managed stands a year after the management application. This indicated that the rust fungus fruited on Melampyrum more abundantly in forest stands that had the highest tree density prior to its fruiting. The results provide basic information of rust incidence in forest stands shortly after their management. The long-term effect of the different forest management types on rust incidence both on pines and alternate hosts will be assessed periodically years later. Keywords: alternate hosts; Melampyrum pretense; Melampyrum sylvaticum; Pinus sylvestris; rust diseases; Scots pine blister rust

The Diversity and Floristic Analysis of Rust Diseases in the Sanjiangyuan Forest Plants.

Between 2020 and 2023, rust fungus specimens were collected from the primary forested regions of the Sanjiangyuan area in Qinghai Province, resulting in over 300 samples. A taxonomic and phylogenetic study of the rust fungi from these forests was conducted using morphological and molecular biological techniques. The investigation identified rust fungi from 7 families, 12 genera, 56 species and varieties, including 10 new host records, 1 new record for China, and 2 novel species. The host plants involved belonged to 26 families, 48 genera, and 78 species. Pucciniaceae and Coleosporiaceae were the dominant families, with the genera Puccinia, Melampsora, and Gymnosporangium being prevalent. The rust fungi in the Sanjiangyuan forests showed a biogeographical affinity with the North Temperate Zone. Floristic comparisons revealed a higher similarity with rust fungi from Inner Mongolia, Gansu, and Tibet and a lower similarity with those from Hainan. An analysis of the life forms of rust fungus host plants indicated that herbaceous plants were the most common, followed by shrubs and trees. In different regions of Sanjiangyuan, rust fungi were found as follows: Golog Prefecture with 6 families, 9 genera, and 28 species; Yushu Prefecture with 5 families, 8 genera, and 31 species; Huangnan Prefecture with 5 families, 9 genera, and 26 species; and Hainan Prefecture with 4 families, 5 genera, and 10 species. The families Pucciniaceae, Melampsoraceae, and Coleosporiaceae were common across all four regions. Moreover, the families Rosaceae, Asteraceae, Ranunculaceae, Salicaceae, and Caprifoliaceae were shared among the host plants in these regions.