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Global climate change influences the emergence, spread, and severity of rust diseases that affect crops and forests. In Korea, the rust diseases that affect Wisteria floribunda and its alternate host Corydalis incisa are rapidly spreading northwards. Through morphological, molecular, phylogenetic, and pathogenicity approaches, Neophysopella kraunhiae was identified as the causal agent, alternating between the two host plants to complete its life cycle. Using the maximum entropy model (Maxent) under shared socioeconomic pathways (SSPs), the results of this study suggest that by the 2050s, C. incisa is likely to extend its range into central Korea owing to climate shifts, whereas the distribution of W. floribunda is expected to remain unchanged nationwide. The generalized additive model revealed a significant positive correlation between the presence of C. incisa and the incidence of rust disease, highlighting the role that climate-driven expansion of this alternate host plays in the spread of N. kraunhiae. These findings highlight the profound influence of climate change on both the distribution of a specific plant and the disease a rust fungus causes, raising concerns about the potential emergence and spread of other rust pathogens with similar host dynamics.

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This study aims at the identification and characterization of five actinobacterial strains with presumed belonging to the species Curtobacterium flaccumfaciens isolated from tomato and pepper plants, and establishing the potential role of both plants as natural reservoirs of this phytopathogen. Species identification was performed via MALDI-ToF MS, 16S rDNA sequencing and PCR. The strains were Gram-positive with a coryneform cell shape having yellow/orange-pigmented colonies; positive for catalase and esculin, and starch and casein hydrolysis; oxidase-, urease-, indole- and nitrate-reduction-negative and were strictly aerobic. All isolates produced antimicrobial substances against various phytopathogenic bacteria. Tomato and pepper plants were artificially infected with newly isolated strains in order to establish their role as natural reservoirs of the bacteria. Morphological alterations were observed only in the tomato plants, with defoliation of the first two to four leaves at the 28th day. Then, viable coryneform bacterial isolates (n = 73) were successfully re-isolated only from the stems of the infected plants. The similarity between the re-isolates and the respective initial isolates was confirmed phenotypically and genotypically by RAPD-PCR, confirming that solanaceous vegetables can act as reservoirs of C. flaccumfaciens. This is the first report of C. flaccumfaciens in Bulgaria.

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Tomato interveinal chlorosis virus (ToICV; Begomovirus solanumintervenae, genus Begomovirus, family Geminiviridae) has been described infecting tomato (Solanum lycopersicum) and Macroptilium lathyroides in Northeastern (NE) Brazil for more than a decade (Albuquerque et al., 2012; Silva et al., 2012). During a survey in 2020, plants of the leguminous weed Rhynchosia minima exhibiting virus-like symptoms such as mosaic and interveinal chlorosis were observed in the state of Alagoas, NE Brazil. Symptomatic leaf samples of R. minima were randomly collected (n=15; supplementary figure 1). Total DNA from each sample was used as a template for PCR amplification of partial begomoviral DNA-A sequences using the degenerate primer pair PAL1v1978 and PAR1c496, universal for geminiviruses (Rojas et al., 1993). Amplicons of ~1.2 kbp were observed from 12 samples, although this should not be considered as incidence since only symptomatic plants were collected. To identify the begomovirus associated with R. minima, viral genomes were amplified from PCR-positive samples using rolling circle amplification (RCA) (Inoue-Nagata et al., 2004). The RCA products were digested with HindIII, cloned into the pBluescript II KS+ plasmid vector and bidirectionally Sanger-sequenced (Macrogen Inc., Seoul). BLASTn searches indicated that the clones (n=4) reported here corresponded to a begomovirus DNA-A component, and pairwise comparisons showed that they shared the highest identity with ToICV, at 92.4-94.7% nucleotide sequence identity. Based on the species demarcation criteria of ≥91% nucleotide identity for the genus Begomovirus (Brown et al., 2015), the begomoviruses obtained from R. minima are new isolates of ToICV. The new DNA-A sequences of 2,619-2,623 nt in length were deposited in GenBank under accession numbers PP639092 to PP639095. Multiple nucleotide sequence alignments were prepared using the MUSCLE algorithm implemented in MEGA v.11 (Kumar et al., 2018), and a maximum likelihood (ML) tree was reconstructed in RaxML-NG (Kozlov et al., 2019), assuming a general time reversible (GTR) nucleotide substitution model with a gamma (G) model of rate heterogeneity and 1,000 bootstrap replicates. The DNA-A-based tree showed that the ToICV sequences clustered into a monophyletic group, additionally supporting these isolates as members of the species Begomovirus solanumintervenae. At least two independent interspecies recombination events were predicted among the ToICV isolates, with breakpoints located in the Rep-encoding region and ToICV (GenBank Accession JF803253), tomato mottle leaf curl virus (JF803248) and soybean blistering mosaic virus (MN486865) detected as putative parents. To the best of our knowledge, this is the first report of ToICV infecting R. minima worldwide, expanding the host range of this begomovirus. Non-cultivated plants such as R. minima play a crucial role as reservoirs and sources of inoculum for begomoviruses (Paz-Carrasco et al., 2014), reinforcing their relevance to socioeconomically important crops.

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Rust disease poses a major threat to global agriculture and forestry. It is caused by types of Pucciniales, which often require alternate hosts for their life cycles. Nyssopsora cedrelae was previously identified as a rust pathogen on Toona sinensis in East and Southeast Asia. Although this species had been reported to be autoecious, completing its life cycle solely on T. sinensis, we hypothesized that it has a heteroecious life cycle, requiring an alternate host, since the spermogonial and aecial stages on Aralia elata, a plant native to East Asia, are frequently observed around the same area where N. cedrelae causes rust disease on T. sinensis. Upon collecting rust samples from both A. elata and T. sinensis, we confirmed that the rust species from both tree species exhibited matching internal transcribed spacer (ITS), large subunit (LSU) rDNA, and cytochrome oxidase subunit III (CO3) mtDNA sequences. Through cross-inoculations, we verified that aeciospores from A. elata produced a uredinial stage on T. sinensis. This study is the first report to clarify A. elata as an alternate host for N. cedrelae, thus providing initial evidence that the Nyssopsora species exhibits a heteroecious life cycle.

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Wheat stripe rust is an airborne and destructive disease caused by a heteroecious rust fungus Puccinia striiformis f. sp. tritici (Pst). Studies have demonstrated that the rust pathogen accomplishes sexual reproduction on susceptible barberry under natural conditions in spring, whereas Pst infection on barberry is still in blank in other seasons. In late October 2016, aecial production on barberry shrubs were observed in Linzhi, Tibet, China. Therefore, experimental tests were conducted to verify the existence of sexual cycles of Pst in this season. By inoculating 52 aecial clusters from 30 rusted barberry leaves, four Pst samples, T1 to T4, were successfully recovered from the rusted barberry shrubs. Sixty-five single uredinium (SU) isolates were derived from the four Pst samples. Based on virulence tests on the Chinese differential hosts, T1 to T4 samples were unknown races and showed mixed reactions on some differentials. Twenty-one known races and 44 unknown races belonging to five race groups were identified among the 65 SU isolates. Meanwhile, the 65 SU isolates produced 26 various virulence patterns (VPs; called VP1-VP26) on 25 single Yr gene lines and 15 multilocus genotypes (MLGs) at nine simple sequence repeat marker loci. Clustering analysis showed similar lineage among subpopulations and different lineage between subpopulations. Linkage disequilibrium analysis indicated that the SU population was produced sexually. This study first reported that Pst infects susceptible barberry to complete sexual reproduction in autumn. The results update the knowledge of disease cycle and management of wheat stripe rust and contribute to the understanding of rust genetic diversity in Tibet.

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The comeback of wheat stem rust in Europe, caused by Puccinia graminis f. sp. tritici, and the prevalence of the alternate (sexual) host in local areas have recently regained attention as a potential threat to European wheat production. The aim of this study was to investigate a potential epidemiological link between the aecia found on an indigenous barberry species and stem rust infections on nearby cereals and grasses. Aecial infections collected from Berberis vulgaris subsp. seroi were inoculated on a panel of susceptible genotypes of major cereal crop species. In total, 67 stem rust progeny isolates were recovered from wheat (51), barley (7), and rye (9), but none from oat, indicating the potential of barberry derived isolates to infect multiple cereals. Molecular genotyping of the progeny isolates and 20 cereal and grass stem rust samples collected at the same locations and year, revealed a clear genetic relatedness between the progeny isolated from barberry and the stem rust infections found on nearby cereal and grass hosts. Analysis of Molecular Variance indicated that variation between the stem rust populations accounted for only 1%. A Principal Components Analysis using the 62 detected multilocus genotypes also demonstrated a low degree of genetic variation among isolates belonging to the two stem rust populations. Lastly, pairwise comparisons based on fixation index (Fst), Nei's genetic distances and number of effective migrants (Nm) revealed low genetic differentiation and high genetic exchange between the two populations. Our results demonstrated a direct epidemiological link and functionality of an indigenous barberry species as the sexual host of P. graminis in Spain, a factor that should be considered when designing future strategies to prevent stem rust in Europe and beyond.

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The increased emergence of cereal stem rust in southern and western Europe, caused by the pathogen Puccinia graminis, and the prevalence of alternate (sexual) host, Berberis species, have regained attention as the sexual host may serve as source of novel pathogen variability that may pose a threat to cereal supply. The main objective of the present study was to investigate the functional role of Berberis species in the current epidemiological situation of cereal stem rust in Europe. Surveys in 11 European countries were carried out from 2018 to 2020, where aecial infections from five barberry species were collected. Phylogenetic analysis of 121 single aecial clusters of diverse origin using the elongation factor 1-α gene indicated the presence of different special forms (aka formae speciales) of P. graminis adapted to different cereal and grass species. Inoculation studies using aecial clusters from Spain, United Kingdom, and Switzerland resulted in 533 stem rust isolates sampled from wheat, barley, rye, and oat, which confirmed the presence of multiple special forms of P. graminis. Microsatellite marker analysis of a subset of 192 sexually-derived isolates recovered on wheat, barley and rye from the three populations confirmed the generation of novel genetic diversity revealed by the detection of 135 multilocus genotypes. Discriminant analysis of principal components resulted in four genetic clusters, which grouped at both local and country level. Here, we demonstrated that a variety of Berberis species may serve as functional alternate hosts for cereal stem rust fungi and highlights the increased risks that the sexual cycle may pose to cereal production in Europe, which calls for new initiatives within rust surveillance, epidemiological research and resistance breeding.

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Tomato brown rugose fruit virus (ToBRFV; genus, Tobamovirus, family, Virgaviridae) was first reported in 2015 infecting tomatoes grown under protected cropping in the Jordan Valley. Since then, ToBRFV has been detected in tomatoes grown in both protected and open fields across Jordan. The increased incidence of ToBRFV prompted this investigation of the potential role of natural weed hosts in the dissemination of ToBRFV. A survey was conducted in the Jordan Valley and highlands to determine possible reservoir hosts of ToBRFV in fields and greenhouse complexes in which tomatoes were grown. Detection of ToBRFV infection was made by double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) and further confirmation by reverse-transcription polymerase chain reaction (RT-PCR), followed by DNA cloning and sequencing, and bioassays. Thirty weed species belonging to twenty-six genera from sixteen families were tested. Twelve species belonging to eight families were infected of which ten species are newly reported hosts for ToBRFV. Seed transmission of ToBRFV in Solanum nigrum was confirmed in a grow-out experiment. To our knowledge, this is the first report of the natural occurrence of ToBRFV on weed hosts. Identification of natural reservoirs of ToBRFV can help to develop management practices focused on weed plant species to prevent ToBRFV transmission. The extent to which ToBRFV survives in diverse alternate weed host species outside tomato growing seasons in different world regions requires further research in order to establish the risk associated with the possible contribution of weeds as a reservoir for primary infections in tomato crops.

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Many Berberis species have been identified as alternate hosts for Puccinia striiformis f. sp. tritici. Importantly, susceptible Berberis species are determined to play an important role in the occurrence of sexual reproduction, generation of new races of the rust pathogen. However, little is known about Mahonia serving as alternate hosts for P. striiformis f. sp. tritici and their role to commence sexual reproduction of the rust fungus under natural conditions. Herein, three Mahonia species or subspecies, Mahonia fortunei, M. eurybracteata subsp. ganpinensis, and M. sheridaniana, were identified as alternate hosts for P. striiformis f. sp. tritici, and seven Mahonia species were highly resistant to the rust pathogen. We recovered seven samples of P. striiformis f. sp. tritici from naturally rusted Mahonia cardiophylla plants. Totally, 54 single uredinium (SU) isolates, derived from the seven samples, generated 20 different race types, including one known race type, and 19 new race types. SNP markers analysis showed that all SU isolates displayed high phenotype diversity (H = 0.32) with a high Shannon's information index (I = 0.49). Analysis of linkage disequilibrium indicated an insignificant rbarD value (rbarD = 0.003, P < 0.1). As a result, all SU isolates are sexually produced, suggesting that P. striiformis f. sp. tritici parasitizes susceptible Mahonia to complete sexual reproduction under natural conditions. The role of Mahonia in occurrence of wheat stripe rust are needed to study for management of the disease.

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Corydalis acuminata Franch., C. edulis Maxim. and C. racemosa (Thunb.) Pers. of family Papaveraceae are rich in multiple alkaloids and widely used as Chinese medicinal herbs, for treating cough, pruritus, sores tinea and snake venom (Zhang et al. 2008, Iranshahy et al. 2014). In April 2021, orange rust pustules were observed on C. acuminata, C. edulis and C. racemosa in Shaanxi Province (34°4'56'' N, 108°2'9'' E, alt. 770 m), China. Samples were collected and voucher specimens were preserved in the Herbarium Mycologicum Academiae Sinicae (nos. HMAS249947-HMAS249949), China. Consequent geospatial investigations revealed that diseased plants can be observed at an altitude of 400-1000 m, and show an incidence from 40% to 80% varied by altitude. Spermogonia epiphyllous, subcuticular, densely grouped, oval or round, 0.14-0.36 × 0.09-0.30 mm, pale orange-yellow, and type 3 of Cummins and Hiratsuka (1963). Aecia mostly hypophyllous, subepidermal without peridia, Caeoma-type, erumpent, densely grouped, oval or round, 0.27-0.85 × 0.15-0.43 mm, and orange-yellow; hyaline peridial cells produced in a periphery of the sorus under the ruptured epidermis of host plants. Aeciospores globoid or broadly ellipsoid, catenulate with intercalary cells, 15.7-20.1 × 10.8-15.7 µm, yellow to pale orange; walls hyaline, verrucose, 1.7-3.1 µm thick. This fungus was morphologically identified as Melampsora (Melampsoraceae). The rDNA-28S and the internal transcribed spacer (ITS) regions were amplified using primers NL1/NL4 and ITS1/ITS4 (Ji et al. 2020; Wang et al. 2020). Bi-directional sequences were assembled and deposited in GenBank (accession nos. MW990091-MW990093 and MW996576-MW996578). Phylogenetic trees were constructed with the ITS+rDNA-28S dataset based on maximum-likelihood (ML), maximum-parsimony (MP) and Bayesian Inference (BI). ML and MP bootstrap values were calculated by bootstrap analyses of 1,000 replicates using MEGA-X (Kumar et al. 2018), while BI posterior probabilities (Bpps) were calculated using MrBayes ver. 3.1.2 (Ji et al. 2020; Wang et al. 2020). Phylogenetic analyses grouped our specimens and Melampsora ferrinii Toome & Aime into one clade, highly supported by bootstrap values of ML, MP, and Bpps of 100%/100%/1. Inoculations were conducted with 1-year-old plants of original host, Salix babylonica L. (Toome & Aime 2015). Aeciospores suspension with a concentration of 106 spores/ml were sprayed on 20 healthy leaves, with another 20 healthy leaves sprayed with sterile water as the control. The inoculated plants were kept in darkness at 20-25 °C for 2 days and then transferred into greenhouse at 23°C with 16 h light per day. After 8-10 days of inoculation, yellow pustules of uredinia appeared on abaxial surfaces of the inoculated leaves, which were identical to Toome & Aime (2015) reported, while the control leaves remained healthy. Inoculations with the same method were conducted by spraying urediniospores, and the same rust symptoms developed after 8 days. Genus Corydalis was verified as the alternate host of M. chelidonii-pierotii Tak. Matsumoto, M. coleosporioides Dietel, M. idesiae Miyabe and M. yezoensis Miyabe & T. Matsumoto (Shinyama & Yamaoka 2012; Okane et al. 2014; Yamaoka & Okane 2019), and C. incisa (Thunb.) Pers. was speculated as the potential alternate host of M. ferrinii (Toome & Aime 2015). Based on morphology, phylogeny and pathogenicity, we firstly report M. ferrinii in mainland China and verify C. acuminata, C. edulis and C. racemosa instead of C. incisa as its alternate hosts.

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Barberry (Berberis spp.) is an alternate host for both the stripe rust pathogen, Puccinia striiformis f. sp. tritici (Pst), and the stem rust pathogen, P. graminis f. sp. tritici (Pgt), infecting wheat. Infection risk was assessed to determine whether barberry could be infected by either of the pathogens in Asia and Southeastern Europe, known for recurring epidemics on wheat and the presence of barberry habitats. For assessing infection risk, mechanistic infection models were used to calculate infection indices for both pathogens on barberry following a modeling framework. In East Asia, Bhutan, China, and Nepal were found to have low risks of barberry infection by Pst but high risks by Pgt. In Central Asia, Azerbaijan, Iran, Kazakhstan, southern Russia, and Uzbekistan were identified to have low to high risks of barberry infection for both Pst and Pgt. In Northwest Asia, risk levels of both pathogens in Turkey and the Republic of Georgia were determined to be high to very high. In Southwest Asia, no or low risk was found. In Southeastern Europe, similar high or very high risks for both pathogens were noted for all countries. The potential risks of barberry infection by Pst and/or Pgt should provide guidelines for monitoring barberry infections and could be valuable for developing rust management programs in these regions. The framework used in this study may be useful to predict rust infection risk in other regions.

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Puccinia striiformis f. sp. tritici, which causes yellow (or stripe) rust on wheat, is a macrocyclic and heteroecious fungus. In this study, we investigated whether Berberis vulgaris subsp. seroi and B. vulgaris subsp. australis, which are indigenous in Spain, may serve as alternate hosts for P. striiformis f. sp. tritici. Wheat leaves bearing telia of an isolate of P. striiformis f. sp. tritici were harvested and used to inoculate plants of both barberry subspecies. Pycnia were observed on the adaxial side of the leaves from 10 days after inoculation (dai). Following successful fertilization, aecia were observed on the abaxial side of the leaves from 16 dai. At 27 dai, barberry leaves bearing aecia were detached and used to inoculate susceptible wheat seedlings of cultivar Morocco. Uredinia were observed on wheat seedlings from 12 days after aeciospore exposure. Eighty-three single lesions were recovered from individual wheat leaves, of which 43 were genotyped using 19 P. striiformis f. sp. tritici simple sequence repeat markers (SSR). In total, 19 multilocus genotypes (MLGs) were identified among the 43 progeny isolates. The SSR genotyping confirmed that all 43 isolates were derived from the parental isolate. Seven heterozygous SSR markers showed segregation among the progenies, whereas none of the 12 homozygous markers resulted in segregation. These results demonstrated that B. vulgaris subspp. seroi and australis can serve as alternate hosts for P. striiformis f. sp. tritici, which may result in novel virulence combinations that can have a detrimental impact on wheat production. Although P. striiformis f. sp. tritici has not been detected on these barberry species in nature, this study highlights the importance of rust surveillance in barberry areas where suitable conditions for completion of the sexual life cycle may be present.

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Evaluating alternate hosts that facilitate the persistence of a virus in the landscape is key to understanding virus epidemics. In this study, we explored the role of several plant species (eggplant, pepper, and Palmer amaranth) as inoculum sources of tomato yellow leaf curl virus (TYLCV) and as reservoirs for its insect vector, Bemisia tabaci (Gennadius). All inoculated species were infected with TYLCV, but whiteflies acquired fewer viral copies via feeding from pepper and eggplant than from tomato and Palmer amaranth. Further, back-transmission assays to recipient tomato resulted in TYLCV infection only when TYLCV was acquired from Palmer amaranth or tomato. Analysis suggested that the role of plant species as TYLCV inoculum sources may be determined by the accumulation of viral copies in the plant, and consequently in the insect vector. In addition, results showed that all three alternate species could sustain populations of B. tabaci, while differentially influencing fitness of whiteflies. Eggplant was a superior host for whiteflies, whereas whitefly survival was compromised on pepper. Together, we demonstrate that both plant-virus and plant-vector interactions could influence the role of an alternate host in TYLCV epidemics, and in our region of study we highlight the potential risk of hosts such as Palmer amaranth in the spread of TYLCV.

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Gramineous grasses are a large group of species, many of which act as accessory (secondary) host for a large number of rust fungi, including devastating rust pathogens of cereals. Among the rust fungi, some are known to be heteroecious and have a complete macrocyclic life cycle with five types of spores on distinct plant species, but for many others the complete life cycle is unknown. Puccinia achnatheri-sibirici, a rust fungus infecting grasses in the genus Achnatherum, has been known for only its uredinial and telial stages; however, the other (pycnial and aecial) stages have not been identified. In this study, we demonstrate that P. achnatheri-sibirici is a heteroecious, macrocyclic fungus with the sexual stage on barberry (Berberis spp.) through inoculation. Pycnia and aecia were successively produced on the inoculated barberry plants. Inoculation of Achnatherum extremiorientale leaves with aeciospores produced yellow-orange uredinia with high infection types, whereas inoculation of wheat variety Mingxian 169, highly susceptible to Puccinia striiformis f. sp. tritici which causes stripe rust on wheat, produced chlorotic flecks but no uredinia. The ITS sequence analysis of P. achnatheri-sibirici did not match with any sequence in the NCBI database and had the highest homology with 94% compared to Puccinia brachypodii and Puccinia aizazii. Observations of the uredinial, telial, and basidial stages on A. extremiorientale and pycnial and aecial stages on Berberis shensiana using light and scanning electron microscopes revealed its characteristics. Morphological characteristics of urediniospores and teliospores are most similar with those of P. achnatheri-sibirici described in the literature. This study proved (1) the life cycle of P. achnatheri-sibirici as heteroecious and macrocyclic and the alternate host as barberry; (2) the description of life stages in the sexual cycle, especially the morphologies of aecial, pycnial, and basidial stages; and (3) the expansion of knowledge on the rust flora on barberry.

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Coffee leaf rust (CLR), caused by the fungal pathogen Hemileia vastatrix, has plagued coffee production worldwide for over 150 years. Hemileia vastatrix produces urediniospores, teliospores, and the sexual basidiospores. Infection of coffee by basidiospores of H. vastatrix has never been reported and thus far, no alternate host, capable of supporting an aecial stage in the disease cycle, has been found. Due to this, some argue that an alternate host of H. vastatrix does not exist. Yet, to date, the plant pathology community has been puzzled by the ability of H. vastatrix to overcome resistance in coffee cultivars despite the apparent lack of sexual reproduction and an aecidial stage. The purpose of this study was to introduce a new method to search for the alternate host(s) of H. vastatrix. To do this, we present the novel hypothetical alternate host ranking (HAHR) method and an automated text mining (ATM) procedure, utilizing comprehensive biogeographical botanical data from the designated sites of interests (Ethiopia, Kenya and Sri Lanka) and plant pathology insights. With the HAHR/ATM methods, we produced prioritized lists of potential alternate hosts plant of coffee leaf rust. This is a first attempt to seek out an alternate plant host of a pathogenic fungus in this manner. The HAHR method showed the highest-ranking probable alternate host as Psychotria mahonii, Rubus apetalus, and Rhamnus prinoides. The cross-referenced results by the two methods suggest that plant genera of interest are Croton, Euphorbia, and Rubus. The HAHR and ATM methods may also be applied to other plant-rust interactions that include an unknown alternate host or any other biological system, which rely on data mining of published data.

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Since 2012, frequent outbreaks of Hematodinium diseases have significantly impacted sustainable culture of marine crabs Portunus trituberculatus in the coastal areas of Shandong Peninsula. The mechanisms of the Hematodinium parasite epizootics in polyculture pond systems remain to be explored and alternate crustacean hosts are speculated to play important roles in transmission and epizootiology of the disease. To investigate their possible role in transmission, the common wild mudflat crabs Helice tientsinensis were sampled from the waterway connecting to polyculture ponds in Huangdao, Qingdao, China and diagnosed for Hematodinium infection. Hematodinium infection was found in H. tientsinensis collected in the waterway from April-November 2018, with a prevalence of 5.8-31.7%. In addition, 23.1% of H. tientsinensis sampled from the adjacent polyculture pond were infected during the peak of the Hematodinium epizootic in July. Amoeboid trophonts or prespores were observed in the hemolymph of the Hematodinium-infected crabs and histopathological changes were observed in major organs (e.g. hepatopancreas, heart, gill and muscle). The ITS1 rRNA of Hematodinium sp. infecting H. tientsinensis shared 99-100% similarity to isolates infecting P. trituberculatus and Penaeus monodon in local polyculture ponds, and are included in a monophylogenetic clade, Hematodinium perezi genotype II, in the phylogenetic tree. The results further showed that this generalist parasite was infecting various types of marine crustaceans in the coastal waters of China, and that mudflat crabs H. tientsinensis may serve as an important alternate host during epizootics of Hematodinium parasites in the polyculture system.

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Puccinia striiformis f.sp. tritici (Pst) is the causal agent of stripe (yellow) rust on wheat. It seriously threatens wheat production worldwide. The obligate biotrophic fungus is highly capable of producing new virulent races that can overcome resistance. Studying the inheritance of Pst virulence using the classical genetic approach was not possible until the recent discovery of its sexual stage on barberry plants. In the present study, 127 progeny isolates were obtained by selfing a representative Chinese Yellow Rust (CYR) race, CYR32, on Berberis aggregate. The parental isolate and progeny isolates were characterized by testing them on 25 wheat lines with different Yr genes for resistance and 10 simple sequence repeat (SSR) markers. The 127 progeny isolates were classified into 27 virulence phenotypes (VPs), and 65 multi-locus genotypes (MLGs). All progeny isolates and the parental isolate were avirulent to Yr5, Yr8, Yr10, Yr15, Yr24, Yr26, Yr32, and YrTr1; but virulent to Yr1, Yr2, Yr3, Yr4, Yr25, Yr44, and Yr76. The VPs of the parental isolate to nine Yr genes (Yr6, Yr7, Yr9, Yr17, Yr27, Yr28, Yr43, YrA, and YrExp2) and the avirulence phenotype to YrSP were found to be heterozygous. Based on the segregation of the virulence/avirulence phenotypes, we found that the VPs to Yr7, Yr28, Yr43, and YrExp2 were controlled by a dominant gene; those to Yr6, Yr9, and YrA (Yr73, Yr74) by two dominant genes; those to Yr17 and Yr27 by one dominant and one recessive gene; and the avirulence phenotype to YrSP by two complementary dominant genes. Molecular mapping revealed the linkage of 10 virulence/avirulence genes. Comparison of the inheritance modes of the virulence/avirulence genes in this study with previous studies indicated complex interactions between virulence genes in the pathogen and resistance genes in wheat lines. The results are useful for understanding the plant-pathogen interactions and developing wheat cultivars with effective and durable resistance.

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With the objective of encouraging the use of rabbits as alternative hosts for the cattle tick, four rabbits were infested on the ears and back. From the second day of infestation the developmental stages were observed. e duration of larval engorgement and changes were estimated between six and eight days in the region of the back and between 've and seven days in the pinna. e nymphal engorgement and changes occurred at approximately 10.80 ± 2.65 days in the dorsal and 11.00 ± 2.52 days in the ear, with the engorgement of adults and copulation occurring at 7.03 ± 2.45 days, on the dorsal region and 8.55 ± 1.82 days in the region of the pinna. e parasitic period ranged from 21 to 29 days (back) and from 23 to 30 days (pinna). e engorged females of the back and ear weighed on average 34.43 ± 18.73 and 36.30 ± 18.10 mg, respectively. e nutritional and reproductive e/ciency indexes were 17.38 ± 14.27 and 26.85 ± 17.13% (back) and 17.42 ± 12.22% and 30.70 ± 19.80% (pinna). Although not appropriate to maintain successive generations of Rhipicephalus (Boophilus) microplus, rabbits can be used for di:erent stages of engorgement of the ixodid, allowing experimental studies.

Com objetivo de viabilizar o uso de coelhos como hospedeiros alternativos do carrapato bovino, foram infestados quatro coelhos nas orelhas e no dorso. A partir do segundo dia da infestação, foram observados os estágios de desenvolvimento dos carrapatos. A duração do ingurgitamento e muda larval foi estimada entre seis e oito dias na região do dorso e entre cinco e sete dias no pavilhão auricular. O ingurgitamento e muda ninfal ocorreram em aproximadamente, 10,80 ± 2,65 dias na região dorsal e 11,00 ± 2,52 dias no pavilhão auricular; e o ingurgitamento e cópula dos adultos ocorreu em 7,03 ± 2,45 dias, na região do dorso e em 8,55 ± 1,82 dias na região do pavilhão auricular . O período parasitário variou de 21 a 29 dias (dorso) e de 23 a 30 dias (pavilhão auricular). As fêmeas ingurgitadas do dorso e orelha pesaram, em média, 34,43 ± 18,73 e 36,30 ± 18,10 mg, respectivamente. Os índices de e'ciência reprodutiva e nutricional foram de 17,38 ± 14,27 e 26,85 ± 17,13% (região do dorso) e de 17,42 ± 12,22% e 30,70 ± 19,80% (pavilhão auricular). Embora não sejam adequados para manter sucessivas gerações de Rhipicephalus (Boophilus) microplus, os coelhos podem ser empregados para o ingurgitamento dos diferentes estádios deste ixodídeo, viabilizando estudos experimentais.

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RESUMEN

Barley, a collateral host of Pyrenophora tritici-repentis (cause of tan spot of wheat), could promote genetic variation in the fungal population and serve as a reservoir of local primary inoculum for a wheat crop in the next season. Samples of diseased barley leaves were collected from 35 locations in North Dakota during the 1999 growing season. P. tritici-repentis was recovered from 2 to 5% of the sampled lesions taken from three of the samples. The majority of the samples also harbored Pyrenophora teres, Stagnospora nodorum, and Cochliobolus sativus. All 10 isolates of P. tritici-repentis recovered from the samples were grouped as race 1, because they induced both necrosis and chlorosis on the appropriate wheat differentials. In addition, 12 barley cultivars were tested for their reaction to five races of P. tritici-repentis, and all were resistant. The fungus could not be recovered when isolations were later attempted from the inoculated leaves. Barley cultivars also were infiltrated with two host-specific toxins, Ptr ToxA and ToxB. They were insensitive, because they did not develop necrosis or chlorosis to the toxins. Our results indicate that barley is highly resistant to the fungus and is unaffected by its host-specific toxins. Prevalence of race 1 in a very low frequency on barley during the growing season suggests that barley does not play a significant role in tan spot epidemiology on wheat or promote variation in the fungal population.

RESUMEN

Some common legumes and weeds indigenous to peach orchards in South Carolina were tested in greenhouse experiments to determine their host suitability for Criconemella xenoplax. Legumes that were hosts for the nematode were dwarf English trefoil (Lotus corniculatus var. arvensis), big trefoil (L. uliginosis), birdsfoot trefoil (L. corniculatus), narrowleaf birdsfoot trefoil (L. tenuis), ball clover (Trifolium nigrescens), rose clover (T. hirtum), subterranean clover (T. subterraneum), striate lespedeza (Lespedeza striata), and partridge pea (Cassiafasciculata). Most nonleguminous plants tested did not support population increases, but small increases were observed on orchardgrass (Dactylis glomerata), broadleaf signalgrass (Brachiaria platyphylla), purslane (Portulaca oleracea), and Carolina geranium (Geranium carolinianum). Results indicate that leguminous plants probably should not be used as ground cover or rotation crops for plants that are injured by C. xenopax.